FUNCTIONAL RELIABILITY EVALUATION FOR INSULATED POWER CABLE SYSTEMS
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- UNDERGROUND SYSTEMS INC
- Filing Date
- 2023-11-10
- Publication Date
- 2026-05-19
Smart Images
Figure MX434363B0
Abstract
Description
FUNCTIONAL RELIABILITY EVALUATION FOR CABLE SYSTEMS INSULATED POWER SUPPLIES QQfrRnn / frznz / q / υιλι (1) FIELD OF THE INVENTION [1] This invention relates to high voltage electrical cables and methods and apparatus for evaluating the functional reliability of the grounding and metal shield bonding configurations of such cables. (2) BACKGROUND OF THE INVENTION [2] High voltage electrical power cables for underground applications are comprised of a high voltage electrical conductor, covered in sequence with electrical insulation, a metallic shield, and a protective jacket. A typical AC high voltage circuit includes three individual phase high voltage cables installed in separate conduits that are enclosed in a common duct bank, forming an underground three phase AC cable circuit for interconnecting utility substations, overhead lines, and submarine cable transitions. Manufactured lengths of these cables are limited by packaging, shipping, and installation constraints, and as such, the resulting cable circuit is comprised of segments, or sections, along a cable route generally separated by manholes where each of the individual phases (A, B, and C) is spliced to another segment of the same phase.Each segment can extend for several meters, for example, hundreds of meters, or kilometers. [3] In its simplest configuration, each phase of the cable circuit is comprised of a high-voltage conductor surrounded by electrical insulation, which is in turn surrounded by a conductive shield and a non-metallic protective jacket. That is, the conductor segment of one phase (e.g., phase A) is concentrically surrounded by a corresponding shield segment (also of phase A), and both the conductor and shield extend along a length of the high-voltage cable circuit. The shield is intended to confine the electrical stress to the electrical insulation of the cable and to provide a suitable return path for the system fault current. [4] The cable shield may be earthed at more than one point along the circuit length (multi-point earthed arrangement), but this results in current flowing in the cable shield between the earthed points. The amount of current flowing in the shield will depend on the arrangement of the phase conductors within the duct bank, the electrical conductivity of the cable shields, and the charging current flowing in the high-voltage cable conductor. This induced shield current may be high enough to produce undesirable heat loss in the shields and limit the QQfrRnn / frznz / q / υιλι ampacity (current carrying capacity) of the cable circuit. [5] Alternatively, the cable shield may be physically connected to electrical ground at only one point along the circuit length (single-point ground configuration). In this configuration, there is no circulating current to limit the cable ampacity. However, in this single-point ground configuration, the induced shield voltage increases with distance from the grounding point. This shield voltage also depends on the physical separation between the cable phases and the conductor load current. The induced shield voltage can be quite high even under normal loads, reaching damaging levels during faults and transient overvoltage conditions.To minimize or prevent damage due to high shield voltages, such as can occasionally arise due to load switching or lightning, a surge suppressor, often referred to as a shield voltage limiter (SVL), is typically installed at the most easily accessible ungrounded end of the shield. The SVL limits transient potential differences that occur between the shield and ground to acceptable levels. SVLs are composed of ceramic metal oxide blocks that can be characterized as exhibiting nonlinear resistance. QQfrRnn / frznz / q / υιλι decreasing resistance values as the voltage across the SVL increases beyond its conduction threshold voltage. SVLs come in various voltage and energy capacity classes. They can be thought of as behaving as an open circuit during normal power operation and a short circuit during transient overvoltages when the potential across the SVL exceeds its conduction threshold voltage. As is known, normal power operation of high-voltage cable refers to the typical frequency of 60 Hz or 50 Hz (i.e., the power frequency) of the current flowing in the cable. [6] In a single-point ground configuration, SVLs are installed between the end of an ungrounded shield segment and ground to restrict potential overvoltages to levels well below the dielectric strength of the cable jacket. SVLs consequently protect cable jackets against faults resulting from high-voltage transients. Cable splices joining consecutive segments contain a shield interruption gap, referred to as a shield break, which effectively isolates the respective shield segments from each other, allowing them to operate at different potentials. As such, these gaps should survive transient overvoltages. [7] SVLs are nonlinear devices that have a characteristic voltage-current relationship that is well defined and understood. The resistance of the SVL depends on the QQbRnn / bznz / q / uλι voltage applied across the device. Once the SVL's conduction threshold voltage is exceeded, any increase in voltage results in a disproportionately increasing current. The energy imparted during conduction is dissipated by the SVL as heat. Below its conduction threshold voltage, the current through the SVL is capacitive, out of phase, and proportional to the voltage across the SVL. This current is at such a low level (less than 1 milliamp) that during normal operation substantially no energy is dissipated, and no temperature increase is detectable at the SVL surface. However, as the voltage across the SVL progressively increases and crosses the conduction threshold voltage level, the SVL behaves resistively with exponentially increasing current shifting toward being in phase with the voltage, generating heat that will cause the SVL surface temperature to rise.This increase in surface temperature can be observed even when the SVL is subjected to very short-duration transient overvoltages at voltage levels below its rated power capacity. This is normal, and cooling occurs after the overvoltage dissipates. [8] Additionally, the current through the SVL is out of phase with the voltage across the SVL. [9] In a cross-bonded configuration, shield ground continuity is maintained from end to end while QQfrRnn / frznz / q / υιλι that the shield segments of each phase conductor are connected (or cross-bonded) in order to minimize current flow in the cable shield system. Cross-bonding is provided at two manholes, preferably located at the 1 / 3 point and the 2 / 3 point between the grounded points along the circuit length. In this cross-bonded configuration, the net vector sum of the induced voltage in the shield from each of the three phases is zero, no current flows in the cable shields, and little measurable voltage occurs between the cross-connected points of the shields and ground.
[10] However, under fault conditions or transient voltage events, the cable shield circuit is not phase balanced and the resulting voltages and currents will not follow expectations based on normal power frequency operations. These events are very short in duration and would be of no consequence from a ratings perspective, but may result in damaging high shield voltages.
[11] To facilitate cross-bonded shield configuration, the continuity of the cable shield around each phase conductor is interrupted (the shield break gap) at the cross-bond points to allow the shield of one phase to be connected to the shield of a different phase. This shield break allows the QQbRnn / bznz / q / υιλι shield segments operate at different potentials and should have adequate dielectric strength to survive overvoltage transients. SVLs are used to restrict shield voltages to safe withstand levels for both the cable jacket and shield breakdown. Although cable shield voltages are typically below 100 volts during normal operation, the dielectric strength of the components protected by the SVL for overvoltage transients is designed to be greater than 20 kV. SVLs, when installed, restrict voltages to levels well below the withstand strength for the cable shield system components.
[12] Cable shield arrangements consisting of cross-bonded and single-point grounded configurations may be applied together on the same circuit to achieve the highest ampacity for the circuit. As an example, three cable sections or segments configured in a cross-bonded shield arrangement may also include a subsequent segment configured as a single-point grounded shield segment, which would result in minimal or virtually no shield current across these four segments.
[13] Junction boxes are sealed enclosures that encapsulate the hardware associated with cross-bonding and grounding the cable shields and SVLs used for QQfrRnn / frznz / q / uyl protect cable jackets and shield breaks from faults. They often contain removable conductive links to facilitate shield reconfigurations and out-of-service maintenance testing of cable jackets and shield break separations. Jacket dielectric failure, shield breaks, or SVLs can result in cable shield currents and associated heat losses in the shields that are not accounted for in the cable's operational ratings, resulting in higher than expected cable operating temperatures. Damage to the SVL can occur from sustained overvoltage (extended operation in the SVL conduction transition region) and from exposure to transients greater than the levels the SVL can safely handle. These conditions lead to internal heating of the SVL, degradation, and possible failure of the SVL.
[14] Junction boxes are typically located in manholes where the cable and shield segments are joined by splicing hardware. Accessing the manhole requires de-energizing the high voltage cable circuit, removing any water present in the manhole, performing gas testing, adhering to important safety precautions, and servicing the cable circuit and shield, all in a very confined space. As such, operational checks, consisting of periodic inspections outside the manhole, are required. QQfrRnn / frznz / q / uyl Service tests, which may include specific maintenance tests, are time-consuming and expensive, and are rarely performed. In many cases, component failures in the junction box are discovered during post-failure investigations. It is not unusual to find a junction box filled with water during periodic inspection and post-failure inspection, effectively short-circuiting all internal components.
[15] Detectors for making in-situ measurements of the current flowing through interconnected shield segments, the current flowing from a bonding box to ground, the voltage appearing between the bonding conductor (or cable shield) and ground, the surface temperature of the installed SVL, or the ambient conditions (pressure, temperature, and humidity) existing within the sealed bonding box enclosure are well known and commercially available. However, there is a need to select and package these detectors within the confines of the bonding box enclosure, transmit detector information from such locations, typically below ground level, to a location at which such information is processed and utilized to perform operational validation, or condition assessment, and diagnosis of potential anomalies of the cable shield system, and particularly the SVLs in QQfrRnn / frznz / q / υιλι ese system.
[16] Assessment of the condition of installed SVLs has previously been limited to visual inspection during maintenance outages. This requires entering the manhole where the junction box is located, physically opening the junction box to observe the condition of the junctions and SVLs, and then estimating the operational health (i.e., operational integrity) of the SVLs based on their visual appearance. Recognizing the weakness of this procedure, some utilities simply replace the SVLs and recycle those that subsequent laboratory testing demonstrates to be operationally sound. Field inspection, as currently performed, is of marginal value, labor-intensive, and fraught with safety implications.As a result, inspections are often performed at widely spaced intervals, at best, limiting their value, especially in assessing the condition of installed SVLs.
[17] Remote monitoring of shielding system parameters to identify faulty operation coupled with a field test to verify the operational integrity of SVLs installed in the junction box that do not require manhole entry would provide utilities with a safe, low-cost means and method that could directly or indirectly characterize the performance of the shielding system. QQfrRnn / frznz / q / υιλι electrical cable shielding system and in particular the installed SVLs, thus providing a significant improvement over current conventional practice. BRIEF DESCRIPTION OF THE INVENTION
[18] As an advantage, the present invention provides a means and method for performing out-of-service maintenance testing to determine the functional reliability of the high voltage cable shield system and its associated components including SVLs and to make required repairs or replacements and then confirm that the operation of the system is as designed. The evaluation of conditions and diagnosis of abnormalities in the cable shield system are derived from a combination of detector inputs (e.g., voltage, current, temperature) from detectors preferably deployed within the enclosure (e.g., junction box) into which segments of the cable shield are connected.
[19] The functional reliability, or operational functionality, of an SVL can be determined from its characteristic voltage-current relationship. This voltage-current relationship is measured by applying a step or ramp test voltage to the SVL while monitoring the current flowing through it. At the SVL's conduction threshold voltage, the current increases exponentially, causing the metal oxide blocks to rise in temperature. As such, the QQfrRnn / frznz / q / υιλι voltage-current characteristic of the SVL can be measured directly or inferred through its voltage-temperature characteristic. Temperature detectors, which can be provided to measure the surface temperature of the SVL during normal operation, thereby detecting abnormalities, can be used to monitor the surface temperature of the SVL, thereby monitoring the response of the SVL to a test protocol (i.e., a test voltage) that brings the SVL into its conduction region. The rise in surface temperature can be directly correlated to the current flow of the SVL and as such is an effective means of assessing the functional reliability, or operational integrity, of the SVL.
[20] Information from detectors within the confines of the junction box enclosure, which may be in remote locations including below ground level, is transmitted and used to monitor the condition of the junction box during normal operation. Voltage, current, and temperature information collected during out-of-service maintenance testing can identify SVL abnormalities prior to failure.
[21] Advanced warning of anomalous conditions provides the opportunity to take scheduled corrective action. However, simple warning means are not currently available. The present invention makes it possible QQfrRnn / frznz / q / υιλι possible, using detectors, to measure and monitor the operating and environmental conditions inside the junction box during maintenance tests to verify the operating characteristics of the installed SVLs.
[22] Applying an increasing level of test voltage to the cable shield and measuring the current through the SVL directly or indirectly produces a voltage-current or voltage-temperature characteristic curve for comparison with a new or reference unit. Such SVL characteristics can be measured with the same detectors used to monitor the shield system during normal operation. The present invention employs an in situ test protocol sensitive enough to trace an installed SVL through its characteristic conduction transition region.
[23] An object of the invention is to provide a system and method for detecting, testing, evaluating, diagnosing, and / or reporting, during a system test, the condition of the shielding system, including the enclosures, without requiring the opening of the sealed covers of those enclosures. This is accomplished by transmitting a collection of detector inputs on the electrical and environmental condition of the cable shielding system, including its associated components, to system operators in near real-time using a variety of communications options (including LP-WAN), without accessing QQbRnn / bznz / q / υιλι access openings and sealed covers which could compromise the environmental seals of those enclosures.
[24] Another object of this invention is to provide a maintenance test to stimulate a measurable response indicative of the expected behavior of a functional bonding and grounding arrangement of the cable armor system, and particularly the installed SVLs.
[25] The maintenance test monitors the voltage across and current flowing through the SVL in response to an external test voltage supplied to the cable shield segment. In one embodiment, the SVL current is represented by the heat dissipated by the SVL and detected by a heat detector.
[26] In accordance with one aspect of the invention, the condition of the high voltage cable shield system of a high voltage cable circuit is determined during maintenance testing by electrically disconnecting all operational grounding points from the cable shield segment undergoing maintenance testing, thereby isolating that segment from ground. A test voltage of gradually increasing amplitude is supplied to one end of the insulated shield segment, distant from the covered enclosure housing a connector link to which the ungrounded shield is connected to ground potential by means of a surge arrester. QQbRnn / bznz / q / υιλι shield voltage (SVL). The voltage across the SVL and the resulting surface temperature of the SVL in response to the applied test voltage are monitored and recorded, preferably within the junction box. The condition of the SVL is determined by comparing the voltage-temperature characteristic of the installed SVL to the voltage-temperature characteristic of the same or similar reference SVL or to adjacent SVLs not subjected to the same test voltage.
[27] In accordance with a further feature of this invention, the enclosure or bonding box cross-linking successive shield segments provides electrical connection to a plurality of SVLs installed in the cable circuit.
[28] In one embodiment, at least one other tie box houses a connector link for connecting the shield of the different phase to the shield of yet another phase. Accordingly, the shield of a first phase is electrically connected through the connector link in the first tie box to the shield of a second phase, and the shield of the second phase is connected through the connector link in the other tie box to the shield of a third phase. In this configuration, SVLs in a plurality of the tie boxes may be simultaneously subjected to a test voltage while detectors in the tie boxes monitor the local response of the respective SVLs to that test voltage.
[29] As another feature of this invention, the QQfrRnn / frznz / q / υιλι The condition of the cable shield system is determined at a remote location, where information representing the voltage, current, and temperature of the SVL during routine in-service operation and during an out-of-service maintenance test is transmitted to the remote location for processing and evaluation of the condition of the cable shield system. For example, the voltage, current, and temperature information is transmitted to the remote location by means of a low-power wide area network (LPWAN) or other wireless system; or by fiber optic cable. This information may be combined with similar data from other detectors deployed in the cable circuit and analyzed to establish the operational integrity of the shield grounding and bonding system for the cable circuit.
[30] Various other objects and advantages of the present invention will become apparent from the following detailed description; and novel features will be particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS
[31] The present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
[32] FIGURE 1 illustrates a typical connection, or splice, of a high voltage cable circuit with a break in the QQfrRnn / frznz / q / υιλι shield continuity and SVL;
[33] FIGURE 2 illustrates the construction of a three-phase tie box with SVLs for a single-point shield grounding configuration in which the present invention finds easy application;
[34] FIGURE 3 illustrates a three-phase link box with SVL for a cross-bonded shield configuration in which the present invention finds easy application;
[35] FIGURE 4A is an AC equivalent circuit schematic diagram of parameter detectors installed in a respective shield segment phase in a three-phase cross-bond tie box to provide in-service operational and out-of-service maintenance test data of the cable shield system;
[36] FIGURE 4B is a DC equivalent circuit schematic diagram of parameter detectors installed in a respective shield segment phase in a three-phase cross-bond tie box to provide out-of-service maintenance data of the cable shield system;
[37] FIGURE 4C is a schematic diagram of equivalent DC circuits of parameter detectors installed in a respective shield segment phase in a three-phase cross-bond tie box to provide out-of-service maintenance test data of the cable shield system using a Hall effect current detector; QQfrRnn / frznz / q / υιλι
[38] FIGURE 5 illustrates a three-phase cross-junction box incorporating the parameter detectors schematically illustrated in FIGURES 4A and 4B;
[39] FIGURE 6 is a graphical representation describing the voltage-current characteristics of an SVL over various magnitudes of operational current through the SVL;
[40] FIGURES 7A, 7B and 7C graphically represent the voltage-current characteristic, the voltage-temperature characteristic (surface temperature) and the voltage-power factor characteristic of a typical SVL, particularly illustrating the conduction transition region;
[41] FIGURE 8 illustrates the grounding and bonding configuration of a cross-bonded shield arrangement with three shield segments between the grounding points;
[42] FIGURE 9 schematically illustrates a maintenance test setup in a cross-bonded shield arrangement with three shield segments between ground points;
[43] FIGURE 10 schematically illustrates an alternative maintenance test configuration in a cross-bonded shield arrangement with three shield segments between the ground points;
[44] FIGURE 11 is a simplified schematic illustration of an embodiment for testing cross-bonded shields in accordance with the present invention; QQfrRnn / frznz / q / υιλι
[45] FIGURE 12 is a simplified schematic illustration of the normal operating configuration of the cable shielding system comprised of two single-point grounded cable segments whose condition is evaluated in accordance with the present invention;
[46] FIGURE 13 is a simplified schematic illustration of yet another configuration of the normal operating configuration of the cable shield system comprised of two single point grounded cable segments whose condition is evaluated in accordance with the present invention;
[47] FIGURE 14 is a simplified schematic illustration of a further configuration of the normal operating configuration of the cable shield system comprised of two single point grounded cable segments whose condition is evaluated in accordance with the present invention;
[48] FIGURE 15 is a simplified schematic diagram of a cable shield system containing more than three cross-bonded cable segments;
[49] FIGURE 16 is a simplified schematic diagram of an out-of-service maintenance test setup for a cable armor system containing more than three cross-bonded cable segments;
[50] FIGURE 17 is a schematic illustration of the embodiment of the present invention wherein the functional reliability of the cable shielding system is evaluated in a QQbRnn / bznz / q / υιλι remote location;
[51] FIGURE 18 is a schematic diagram of another out-of-service maintenance test configuration for a cable armor system with a primary section including three secondary sections. DETAILED DESCRIPTION
[52] Turning now to the drawings, where like reference numerals are used throughout, FIGURE 1 illustrates a high voltage cable circuit 102 including two segments, or sections, formed of high voltage conductors 104 and 104' electrically connected by a conductor splice 103 included in the illustrated splice hardware. As appreciated, for high voltage AC transmission, conductors 104 and 104' are of the same phase, e.g., phase A, in a typical three phase transmission system. A conductor insulator 106 surrounds conductor 104 of the illustrated segment of cable circuit 102; and insulator 106 is, in turn, concentrically surrounded by cable shield 108. Likewise, insulator 106' surrounds conductor 104' of the spliced segment and insulator 106' is concentrically surrounded by cable shield 108'. A cable jacket 112, 112' surrounds each respective segment of the cable circuit.
[53] A shield break 118 (or shield interruption separation) electrically isolates the shield segment 108 from the shield segment 108' to interrupt the QQfrRnn / frznz / q / uyl electrical continuity from shield segment 108 to shield segment 108' and prevent current flow between the cable shield segments. The shield break eliminates circulating shield current that would otherwise flow in the shield segment, thereby reducing the ampacity of the cable. The shield break is filled with a dielectric insulating material and allows shield segments 108 and 108' to operate at different voltage potentials. These potential differences, as well as the potential difference that exists between the respective shield segment and ground, are generally low during normal cable circuit operation, but may be large enough to cause dielectric failure of the shield break insulation or cable jackets in the event of power system faults or transient overvoltages caused by lightning and switching surges.Dielectric failure (e.g., short to ground) of shield breaks or cable jackets can lead to unintended current in the cable shield segments that is not accounted for when rating the cable, resulting in higher cable operating temperatures and possible cable failure that can be initiated by arcing and surface carbon buildup caused by arcing, known as tracking between shield segments at the shield break. As is well known, bonding boxes contain the. QQfrRnn / frznz / q / υιλι hardware required to configure grounding and bonding of cable shield segments, including SVLs that are installed to prevent dielectric breakdown by limiting overvoltages to levels that can be sustained without damage to shield breaks and cable jackets.
[54] FIGURE 1 shows a bonding cable 116 of one segment, shown as shield segment 108, physically connected to electrical ground 124 and the bonding cable 116' of the other spliced segment, i.e., shield segment 108', connected through a shield voltage limiter (SVL) 110 to electrical ground 124. For simplicity, the drawing figure illustrates only one of three phases of the high voltage cable circuit. This cable shield connection is typical for each phase in a single point shield grounding configuration. The SVL 110 is housed within an enclosure, preferably a bonding box 114, described below. In other junction box configurations, the bonding cables 116, 116' of the cable shields 108, 108' of the spliced segments may be interconnected via a connector link, as will be described later.
[55] The cable shield system depicted in FIGURE 1 is representative of a single point cable shield grounding configuration whereby the cable shield 108 is grounded at the location of the QQfrRnn / frznz / q / υιλι junction box 114 and is not grounded (isolated from direct ground) at its remote end, i.e., remote from the junction box. Similarly, the cable shield 108' is not grounded (not directly connected to ground) at the junction box 114 and is grounded at a point (not shown) remote from the junction box 114. In bonding box 114, SVL 110 is connected via bonding wire 116' to the ungrounded point of shield 108' to provide a low resistance current path to ground for the surge current in the event the voltage between shield 108' and ground 124 exceeds a critical value, thereby limiting transient voltages between shield and ground and ensuring that such transients do not exceed the dielectric strength of cable jacket 112' or shield break 118.
[56] FIGURE 2 is an illustration of a three-phase tie box configured to support the shield bonding and grounding configuration illustrated in FIGURE 1. As shown, SVLs 110a, 110b, and 110c are electrically and physically connected via bonding wires 116'a, 116'b, and 116'c to cable shields 108'a, 108'b, and 108'c, respectively (not shown). FIGURE 2 also illustrates the connection of common SVL ground conductor 122 to external ground via ground wire 124. As shown, FIGURE 2 illustrates the grounding of the wires QQbRnn / bznz / q / υιλι 116a, 116b and 116c of connection to ground 124 by means of internal connection 122
[57] Turning to FIGURE 3, an example of a cross-bond tie box 314 is illustrated. The tie box is formed as an enclosure with external bonding wire connectors 320a, 320b, 320c projecting outwardly from the interior of the enclosure (as seen in the lower portion of FIGURE 3), through suitable seals, to which bonding wires 116a, 116b, and 116c insulated from the A, B, and C phase shields (108a, 108b, and 108c not shown), respectively, are mechanically and electrically connected. The bonding wire connectors, in turn, connect to connector links 318a, 318b, and 318c, respectively. Alternatively, the bonding wire connectors 320a, 320b, 320c may be located within the housing and the insulated bonding wires 116a, 116b, 116c may be routed through sealable penetrations in the bonding box and connected to connector links 318a, 318b and 318c, respectively.Bonding wire connectors (not shown) project outward from the interior of the enclosure through suitable seals to which bonding wires 116'a, 116'b and 116'c (as viewed on the top side of FIGURE 3) of phase A', B' and C' shields (108'a, 108'b and 108'c not shown), respectively, are mechanically and electrically connected. Connector links 318a, 318b and 318c serve as cross bonding links for connecting bonding wire 116a of. QQfrRnn / frznz / q / υιλι bonding to bonding cable 116'b, bonding cable 116'b to bonding cable 116'c, and bonding cable 116c to bonding cable 116'a, respectively. In this manner, the phase A shield is electrically connected (i.e., cross-linked) to the phase B' shield; the phase B shield is electrically connected to the phase C' shield; and the phase C shield is electrically connected to the phase A' shield. Thus, the shields of the phase A, B, and C cable conductor segments are cross-bonded to the shields of the phase B', C', and A' cable conductor segments, respectively. The shields of phases B', C' and A' are similarly cross-bonded in the next junction box along the length of the circuit to phases C, A and B, respectively (not shown) forming three segments of similar length. The remote ends (not shown) of the cable shields of all three cable shield segments are grounded.In this arrangement, the net induced shield current between the grounded remote ends and the shields will be minimized.
[58] FIGURE 3 also illustrates the connection of the shield voltage limiters (SVLs), collectively referred to as SVLs 310. The SVL 310a is connected to the bonding cable 116a and 116'b via link 318a, thus to the cable shield segments 108a and 108'b. When the SVL is conducting, the SVL provides a low resistance current path for these cable shield segments. QQfrRnn / frznz / q / υιλι 6 ground 324 via the common ground connection 322 for all SVLs. Likewise, the SVL 310b connects to the cable shield 108b and 108'c to provide a low-resistance current path from these cable shield segments to ground. And, the SVL 310c connects to the cable shield 108c and 108'a to provide a low-resistance current path from these cable shield segments to ground. As mentioned above, the SVLs are installed to limit transient overvoltages when they occur on the respective shield segments, primarily as a result of lightning and switching surges.
[59] In an alternative embodiment, bonding cable 116'b may be connected to bonding cable connector 320'a such that, as in the illustrated arrangement, connector link 318a still connects phase A shield to phase B' shield. Similarly, bonding cable 116'c may be connected to bonding cable connector 320'b such that connector link 318b still connects phase B shield to phase C' shield; and bonding cable 116'a may be connected to bonding cable connector 310'c such that connector link 318c still connects phase C shield to phase A' shield.
[60] Proper operation of a high voltage cable shield circuit for single point grounding configuration of cable shields and for the QQfrRnn / frznz / q / υιλι cross-bonded shield configuration, intended to prevent or minimize current flow in cable shields, relies, at least in part, on the proper functioning of SVLs to prevent overvoltage damage to cable jackets and shield breaks. Until now, determination of the functional reliability of junction box components has been based on periodic out-of-service visual and tactile inspection of the hardware and dielectric withstand testing of the shield bonding components. This inspection process requires circuit interruption, traffic control measures, and confined space entry procedures simply to gain physical entry to the manholes where junction boxes are typically located; all before the junction boxes can be physically opened for inspection and subsequent restoration.Consequently, these current inspection methods are labor-intensive and, at best, infrequent. As a result, degraded, damaged, or failed components go undetected until discovered during subsequent investigations due to system failure. The present invention, as discussed below, obviates these problems, resulting in improved evaluation and determination of the functional reliability of the cable armor system and, thus, the overall reliability of the high-voltage cable circuit. QQfrRnn / frznz / q / υιλι
[61] FIGURE 4A is a schematic representation of the parameter detectors installed at each of the three bonding links present in the cross bonding link box shown in FIGURE 3. For simplicity, the detectors installed at connector link 318a and SVL 310a are illustrated. It will be recognized that identical detectors are installed at connector link 318b and SVL 310b and at connector link 318c and SVL 310c.
[62] During normal DC power frequency operation of the high voltage cable (typically operating at 50-60 Hz), any current flowing through the conductor link 318a, connecting the bonding wires 116a to 116'b is detected by a current detector 440a and the voltage appearing across the SVL 310a, electrically connected between the conductor link 318a and the ground 324, is detected by a voltage detector 442a. The current detector 440a may be a conventional current transformer, a Rogowski coil, or any suitable means for quantifying the magnitude of the current flowing through the conductor link. The voltage detector 442a may be a resistive or capacitive voltage divider or other voltage sensing means for quantifying the magnitude of the voltage across the SVL 310a.Preferably, the SVL voltage detected by detector 442a during normal operation of the circuit remains below the threshold voltage of. QQfrRnn / frznz / q / υιλι conduction of the SVL 310a. In this state of operation, the apparent resistance of the SVL 310a is high and the current through the SVL and its associated conduction losses are negligible. The surface temperature of the SVL will remain at room temperature. The ground current detected by a current detector 444a connected from the junction of the SVL and the voltage detector to ground will be only that flowing through the voltage detector 442a, which is negligible at normal operating voltages. It is possible, during power system faults having a duration on the order of milliseconds, for the voltage across the SVL 310a, as measured by the voltage detector 442a, to reach the conduction threshold voltage of the SVL, causing increased current flow through and heating of the SVL 310a.This situation is most likely to occur in the single-point grounded shield arrangement illustrated in FIG. 2, where the SVL is positioned at the ungrounded end of a long cable shield segment grounded at its opposite end. In the event of such an occurrence, the resulting shield voltage is detected by voltage detector 442a and the current flowing to ground as a result of the SVL conduction is detected by current detector 444a. The energy imparted to the SVL during this event causes the surface temperature of the SVL to rise, which is detected by a non-contact infrared temperature detector 446a. QQfrRnn / frznz / q / υιλι possibly a thermocouple. The voltage, current, and temperature rise can be compared to the known voltage-current and voltage-temperature characteristics of the installed SVL, thus indicating the SVL's operability, as will be discussed.
[63] For transient electrical overvoltages (measured in microseconds) caused by switching operations or lightning, which exceed the conduction threshold voltage of the SVL, a transient increase in current is to be expected and the resulting heat will cause the surface temperature of the SVL to rise and subsequently cool. The voltage detector 442a and current detector 444a can capture and measure this voltage and the temperature and current detector 446a will capture the surface temperature rise and subsequent decay.
[64] It will be appreciated by those skilled in the design, installation and maintenance of cable shield bonding and grounding systems that in-service data acquired from the bond current detector 440a, ground current detector 444a, voltage detector 442a and temperature detector 446a of each phase of each bonding box assigned to a specific circuit can provide continuous, near real-time verification of the operation of the in-service cable shield system and can detect abnormalities which may warrant further investigation and possible remediation. QQfrRnn / frznz / q / υιλι
[65] In the discussion above, detectors merely confirm or validate that the junction box and the installed SVL have responded correctly or not during operational events. Although this clearly adds value compared to current practice, the condition assessment here relies on past operational events, i.e., after-the-fact detector information, to detect abnormalities. However, these same detectors used to detect abnormalities due to past occurrences of events, such as transient overvoltages, can be used to assess the functional reliability of installed SVLs by verifying the correct detector response to an external test voltage applied to the cable shield circuit during maintenance testing, as will be described.
[66] FIGURE 4B is the DC equivalent schematic diagram for DC voltages that would appear across the cable shield segments when subjected to out-of-service field maintenance testing using externally applied DC voltages. Under DC conditions, current transformers 440a and 444a, although present, are not functional and therefore, to simplify the drawings, are not shown in the equivalent circuit of FIGURE 4B. In this case, the DC voltage across the cable shield and across the SVL, as a result of the DC voltage QQbRnn / bznz / q / υιλι externally applied, is detected by voltage detector 442a. At voltages below the SVL conduction threshold voltage, negligible current flows through the SVL and no detectable increase in SVL surface temperature will be detected by temperature detector 446a. At voltages exceeding the conduction threshold voltage, the SVL current increases and the heat dissipated by the SVL 310a increases, resulting in an increase in surface temperature detected by detector 446a.
[67] FIGURE 4C is a schematic diagram of one embodiment for directly measuring DC current flow through the SVL. The figure shows a Hall effect device 450a in series with the SVL 310a. Alternatively, the Hall effect device may be positioned, as at 452a, between ground and the junction of the SVL and voltage detector 442a, such as at the same location as the current detector 444a in FIGURE 4A, i.e., at the projecting ground connection 452a, with only a marginal loss in accuracy given the low current associated with the voltage sensing circuitry. Hall effect devices are well known and measure the strength of a magnetic field to produce a proportional voltage output. As such, Hall effect devices may be used for DC and AC current measurements as low as a few milliamps.In one embodiment, a ferromagnetic core is used to concentrate this magnetic field, making it possible to detect a very low level of current. QQfrRnn / frznz / q / υιλι While these devices are typically used to measure current levels on the order of a few amps and up, commercially available instruments are available that will measure in the single digits of milliamps and can be used to calibrate and troubleshoot transducers with outputs of 4-20 milliamps. Hall effect devices are an alternative option to the current transformers discussed above in connection with FIGURE 4A for measuring current flow from the bonding box to external ground. The use of Hall effect devices is particularly advantageous during maintenance testing using a DC voltage source to apply the test voltage. The current information produced by the Hall effect device directly measures the current through the SVL, obviating the need for a surface temperature detector.As the test voltage on line segment 116a detected by voltage detector 442a increases, the current through the SVL, as detected by Hall effect device 450a or alternatively by Hall effect device 452a, also increases, consistent with the characteristics of the installed SVL. This current information is acquired, along with voltage information representing the magnitude of the test voltage across the SVL, thereby establishing voltage-current characteristics of the installed SVL, which can be compared to the voltage characteristics. QQbRnn / bznz / q / υιλι current of a new or reference SVL. As a result of this comparison, the functional reliability of the SVL can be determined.
[68] FIGURE 5 illustrates an embodiment of the junction box of FIGURE 3, including the sensors schematically shown in FIGURE 4A, such as a current sensor 540, similar to current sensor 440 in FIGURE 4A, for measuring the junction current, a current sensor 544, similar to current sensor 444 in FIGURE 4A, for measuring the ground current, a voltage sensor 542, similar to voltage sensor 442 in FIGURE 4A, for measuring the voltage across the SVL, and a temperature sensor 546, similar to sensor 446 in FIGURE 4A, for measuring the surface temperature of the SVL. Atmospheric conditions such as temperature, pressure, and humidity within the junction box housing are measured by one or more environmental sensors (not shown) mounted on a printed circuit board 548.As an example, a microprocessor or other processing circuitry is mounted on the printed circuit board to control the acquisition and storage of detector data. In this example, power to operate the detectors is provided by a battery contained in a sealed, removable housing 560. The embodiment of FIG. 5 also includes a fiber optic communications and control interface 550 coupled to a switchable connector 552. QQfrRnn / frznz / q / uyl operating instructions and data with remote processing circuitry, such as a peripheral controller. Data acquired by the detectors may be analyzed by the processing circuitry individually or in combination with data from other detectors within the same junction box. This data may be processed with similar data acquired from detectors in other junction boxes associated with the same cable circuit to provide utility asset managers with in-service performance indicators (voltage, current, and temperature) under continuous normal operation and also under occasional fault conditions, such as during switching and lightning transient events.
[69] In FIGURE 5, the current flowing through the conductor link is measured by a cascade arrangement of current transformers 540a, 540b, and 540c, the secondary conductors of which form the primary conductors for transformers not shown. This cascade arrangement of current transformers reduces the effective link current, which may be as high as 250 amperes or more, to manageable signal levels on the order of milliamps, to be sent for processing by, for example, a microprocessor, to analyze possible fault conditions. The cascade arrangement of current transformers also improves the voltage withstand capabilities. QQfrRnn / frznz / q / υιλι 6 transient current measurement circuitry.
[70] In the embodiment illustrated in FIGURE 5, each of the voltage detectors is formed by a high voltage resistor connected in series with a low voltage resistor to form a high voltage divider circuit to reduce the actual voltage across the SVL to levels consistent with the input levels normally provided to the microprocessors that receive and process the measured voltages.
[71] In the embodiment shown, temperature detectors 546 are non-contact infrared (IR) detectors disposed proximate respective SVLs 310 to produce output signals representing the surface temperature of the SVLs. The output signals produced by the temperature detectors are coupled to a controller, such as a processor on the printed circuit board (PCB) 548 disposed within the junction box. Alternatively, the output signals may be coupled to a processor disposed outside of the junction box and located in the manhole in which the junction box is located. The temperature detectors detect increases in SVL surface temperature resulting from operation above the SVL conduction threshold voltage that cause an increase in surface temperature.
[72] A voltage relationship is shown in FIGURE 6 QQfrRnn / frznz / q / υιλι Typical current for an SVL. As can be seen from this figure, as the SVL voltage increases over its normal operating range (below the conduction threshold voltage), the current through the SVL increases proportionally. At the conduction threshold voltage, the resistance of the SVL drops and decreases exponentially with increasing voltage, resulting in higher current, greater electrical power loss, and associated increases in the temperature of the metal oxide block forming the SVL. Operating voltages beyond this point are limited by the SVL ratings to progressively shorter durations to ensure that the heat generated by the SVL can be safely dissipated and prevent SVL failure.As shown in FIGURE 6, the normal continuous operating current through the SVL is below 1 milliamp, while switching surges and microsecond duration lightning flashes can be restrained to prevent damage to shield breakdown and cable jackets at lightning discharge levels of 10kA and higher. This voltage-current relationship is representative of virtually all SVLs, and varies only by the voltage at which the SVL enters its conduction transition region, which is approximately 1 milliamp for most SVLs.
[73] FIGURE 7A illustrates the voltage-current (VI) characteristic in the conduction transition region of a 3 kV rated SVL and FIGURE 7B illustrates the QQbRnn / bznz / q / υιλι surface voltage-temperature characteristic that occurs as a result of this SVL current. As shown, the relationship between the electrical and thermal energy curves is very similar. A properly operating kV-rated SVL is expected to follow these curves, and its operability can be confirmed with an in-situ test that takes the SVL through its conduction threshold region while monitoring the resulting current or the SVL surface temperature. SVLs that do not exhibit the expected conduction transition curves can be considered to have poor operational integrity.
[74] As shown in FIGS. 4A through 4C, a Hall effect device may be used as a detector to provide a measurement of the DC current flowing through the SVL. A single Hall effect device 452a placed across the protruding ground connection (FIG. 4C) within the enclosure provides an acceptable DC current measurement; and other known current sensing devices may be used to provide information representing the current flowing through a respective SVL. However, the SVL voltage-temperature relationship proves to be more robust, easier, and less expensive to implement. For the 3 kV rated SVL depicted in FIGS. 7A and 7B, DC voltages across the SVL below 4.5 kV are not expected to generate an appreciable temperature rise. QQfrRnn / frznz / q / υιλι surface, while a DC voltage above 4.5 kV and close to 5 kV would.
[75] Heretofore, out-of-service on-site field maintenance inspection testing of junction boxes requires entry into the manhole in which the junction box is located, and opening the junction box for visual inspection by a technician. The present invention provides a significant improvement over current conventional practice and does not require manhole entry and therefore provides utilities with a safe and low-cost alternative for characterizing the electrical behavior of an installed SVL and thus the functional reliability of the junction box, including that installed SVL.
[76] FIGURE 8 is a simplified diagram illustrating how three secondary shield sections 108a, 108b, 108c are connected in bonding boxes 314 and 815 to form a complete primary cross-bonded shield section. FIGURE 8 illustrates the bonded connection of phase A shield segment 108a of high voltage conductor 104A to phase B shield segment 108b of high voltage conductor 104B via a connector bond 318a in bonding box 314, and the connection of shield segment 108b to phase C shield segment 108c of high voltage conductor 104B via a connector bond 318a in bonding box 314, and the connection of shield segment 108b to phase C shield segment 108c of high voltage conductor 1040 via a connector bond 318b in bonding box 314. QQfrRnn / frznz / q / uyl a connector link 818b in link box 815. In this schematic illustration, each of the link boxes may be of the type shown in FIG. 3 and connector links 318a and 818b may be of the type shown as connector links 318 in FIG. 3. FIG. 8 also schematically illustrates an SVL 310a included in link box 314 for providing a low resistance current path for shield-to-ground bond link 318a when the voltage across the SVL 310a exceeds its conduction threshold voltage. An SVL 810b included in link box 815 provides a similar low resistance current path for shield-to-ground bond link 818b. As is conventional, during normal operation, the shield segment 108a is electrically grounded at a point along the length of the shield, preferably at a point remote from and distant from the bonding box 314.Also, during normal operation, the shield segment 108c is electrically grounded at a point along its length, preferably at a point remote from and distant from the bonding box 815. It should be noted that, for simplicity of drawing, only one of the three cross-connections present in the bonding box 314 and in the bonding box 815 (which are otherwise present as shown in FIGURE 3) is shown in FIGURE 8.
[77] FIGURE 9 is a schematic illustration of one type of maintenance inspection test procedure outside QQfrRnn / frznz / q / υιλι of service used until now. In this test, a segment of the shield, for example, the normally grounded shield segment 108a, is electrically disconnected from ground. Additionally, the point of the shield segment 108c that is normally grounded is disconnected from ground, effectively isolating sections 108a, 108b and 108c from ground. In this test, a voltage source 924 is connected to the shield segment 108c. In accordance with this test procedure, the link boxes 314 and 815 are opened and the SVLs 310a and 810b are disconnected from the connector links 318a and 818b, thereby eliminating the current path to ground for the shield segments 108a, 108b and 108c, via the connected SVLs that could otherwise potentially prevent the test voltages supplied to the cable shield system from source 924 from reaching the desired test voltage level.Since the SVLs are disconnected from the connector links, they are not subjected to the 924 source test voltage, and only the cable jacket and interrupt gaps are tested. Because they are not electrically tested, the SVLs are visually examined and either returned to service or exchanged with new SVLs after maintenance testing. In some cases, the removed SVL is subjected to laboratory testing and recycled if found to be functional.
[78] In the maintenance test procedure QQfrRnn / frznz / q / υιλι above, the test voltage, which is preferably a DC voltage, is increased, for example, in gradual increments to the desired test level and is maintained at that test level for a specified period of time, typically a few minutes. This puts the voltage on the cable jackets and interruption gaps associated with the shield segments 108a, 108b and 108c at the test voltage. After the test is completed, the shield segments are reconnected to ground at the ends of segments 108a and 108c and three other segments (not shown) are isolated from ground and similarly tested.
[79] This out-of-service maintenance test is essentially a dielectric strength test of the cable jacket and interrupting gap performed at a test voltage level above the rated voltage of the SVL and below the designed strength level of the jacket and interrupting gap. As mentioned above, this test procedure requires each junction box to be opened and each SVL to be disconnected or removed, with visual examination of the SVL and connecting hardware, namely, the connector links, bonding wires, and bonding wire connectors in the junction box. The SVLs in the junction boxes may be tested separately and individually to evaluate their proper functioning. This requires specialized equipment and adds significant time to the inspection process. In addition, QQfrRnn / frznz / q / υιλι the need to open and then reseal junction boxes can result in inadequate seals that eventually corrode and otherwise damage the components housed within those junction boxes.
[80] An alternative test arrangement heretofore used to test the cable shield system connected to a bonding box having external bonding cable connections of the type shown in FIGURE 3 is illustrated in FIGURE 10, wherein the bonding boxes 314 and 815 need not be opened for testing and the SVLs need not be disconnected from the connector links (as was the case in FIGURE 9) for the application of a test voltage. In FIGURE 10, the bonding cables 116a, 116b, 116c shown in FIGURE 3 of the respective phases of the shield segments are disconnected from the bonding cable connectors 320a, 320b, 320c and the bonding cables 116'a, 116'b, 116'c are disconnected from the bonding cable connectors 320'a, 320'b, 320'c. Temporary jumpers 1014a and 1015b connect the shield segments 108a, 108b and 108c as shown, thereby bypassing the bonding boxes 314, 815.As a result, the cable jacket and the interruption gaps of the three shield segments are tested together.
[81] As was the case in FIGURE 9, the shield 108a is electrically isolated from ground by disconnecting the point of this shield segment that is normally grounded. QQfrRnn / frznz / q / υιλι Furthermore, the point of the shield segment 108c that is remote from the bonding case 815 and normally grounded is disconnected from ground and the voltage source 924 is coupled to the shield segment 108c. The voltage source 924 shown in FIG. 10 is the same as that illustrated in FIG. 9, typically a DC source, but may be an AC voltage source in either case.
[82] The cable shield system schematically shown in FIGURE 10 is tested in the same manner as previously described for the test procedure of FIGURE 9. The test is performed by gradually increasing the test voltage supplied to the cable shield system by voltage source 924. Although this test configuration avoids the disadvantages associated with opening the covers of the bonding boxes 314 and 815, a technician must nevertheless enter the manholes in which the bonding boxes are located in order to disconnect the external bonding wires, apply temporary jumpers, and possibly, if the bonding box is provided with a transparent cover, perform a cursory visual inspection of the enclosed hardware including the SVL. After the test is performed, the temporary jumpers necessary for testing are removed and the bonding wires are reassembled and resealed.This procedure is also time consuming and subject to error when reconnecting the. QQfrRnn / frznz / q / υιλι bonding cables and reapply sealing materials to the junction boxes.
[83] The above disadvantages and problems of the prior art are avoided by the present invention. An embodiment of the present invention for testing the functional reliability of the cable shield system has the test configuration schematically illustrated in FIG. 11. In this figure, the same reference numerals used in FIG. 8 identify the same components. As shown, the phase A shield 108a is connected by connector link 318a in link box 1114 to the phase B shield 108b; and the phase B shield 108b is connected by connector link 818b in the link box 1115 to the phase C shield 108c. The link box 1114 includes an SVL 310a, a temperature detector 1128a adapted to measure the surface temperature of the SVL 310a, and a voltage detector 1130a adapted to measure the voltage across the SVL 310a.Similarly, the link box 1115 includes an SVL 810b, a temperature detector 1128b, and a voltage detector 1130b. The temperature detectors preferably comprise heat detectors juxtaposed to the SVLs and adapted to detect heat dissipated by the SVL. As mentioned previously, as the voltage across the SVL increases, the current through the SVL will increase linearly until the SVL conduction threshold voltage is reached. At that point, an increase in voltage results in a disproportionate increase in the. QQfrRnn / frznz / q / υιλι current through the SVL which, in turn, produces internal heating and an increase in the detectable temperature of the SVL surface.
[84] In one embodiment, the heat detectors 1128a, 1128b comprise infrared (IR) detectors that detect infrared radiation associated with heat dissipated by the SVLs 310a and 810b. An example of a suitable IR detector is a non-contact infrared detector, such as Melexis model 90614, which produces a signal based on heat radiated from the surface of the SVL. Detection of this heating of the SVL is measured as a change in surface temperature that occurs most rapidly when the applied voltage reaches and exceeds the conduction threshold of the SVL, as is normal and as depicted in FIG. 7B. Detecting an increase in surface temperature above ambient is indicative that the SVL is operating above its conduction threshold, as might occur during abnormal in-service operation above the SVL rating, or during higher magnitude voltage transients.As will be discussed, the test voltages intentionally applied during out-of-service maintenance inspection tests are designed to cause an increase in surface temperature. Such voltage and temperature characterization of the SVL, as detected by the. QQfrRnn / frznz / q / υιλι temperature and voltage detectors, used to confirm the functionality of the cable shielding system and SVLs.
[85] The voltage detector 1130a measures the voltage appearing between the connector link 318a and ground in the link box 1114; and the voltage detector 1130b measures the voltage appearing between the connector link 818b and ground in the link box 1115. It is seen that the monitored voltages are the voltages detected across the SVLs 310a and 810b.
[86] The technique for evaluating the functional reliability of the cable shield system in accordance with the embodiment of the present invention shown in FIG. 11 will now be described. The connection of phase A shield segment 108a to ground is disconnected from ground and the connection of phase C shield segment 108c is likewise disconnected from ground, thereby isolating shield segments 108a, 108b and 108c from ground. A voltage source 1124 similar to voltage source 924 is connected to the isolated shield segments at any point, but preferably at an accessible location above ground level. In FIG. 11, voltage source 1124 is connected to shield segment 108c.
[87] As previously described, the voltage source is applied separately to each of, for example, three main sections with the other two sections grounded to extend the test to include shield breaks and has to be applied sequentially and separately to all sections. QQfrRnn / frznz / q / υιλι main .
[88] In the embodiment where the voltage source 1124 is a DC voltage source, the DC test voltage supplied by this source is increased gradually, such as in a step-wise manner. In one embodiment, the voltage source is controlled such that the DC voltage level supplied to the illustrated cable shield system is known, or predetermined, at each stage. Alternatively, the voltage source 1124 may be controlled by a processor to supply a gradually increasing DC voltage level instructed by that processor. For example, the voltage source 1124 may be one of many commercially available units that have sufficient power to increase the voltage in the cable shield circuit within a few minutes and support the current demand of the SVLs that may be simultaneously brought into their conducting transition region.Alternatively, the voltage source may be an AC voltage source adapted to supply an AC test voltage to the cable shield system. If an AC test voltage is supplied, the current through the SVL and the voltage across the SVL may not be in phase, as mentioned above. The phase angle between the current and the SVL voltage is indicative of the impedance and, more particularly, of the change in impedance. QQfrRnn / frznz / q / υιλι as the SVL is brought into its conduction transition region. This phase angle can be measured; and the phase angle measurement provides voltage and current information supplied to the processing circuitry to determine the functional reliability of the cable shield system.
[89] In one technique for measuring the phase angle between the SVL current and voltage, the zero crossing of the current flowing through the SVL is detected; and the zero crossing of the voltage across the SVL is detected. The time difference between such zero crossings represents the phase angle, or phase shift φ, between the current and voltage. This phase shift is proportional to the power factor pf=cos(φ), which increases as the SVL moves into its conduction region. Consequently, the power factor can be measured, or detected, by detecting the time difference between the zero crossings of the current and voltage. FIGURE 7C shows the increase in power factor associated with the transition of the SVL from capacitive to resistive behavior. As seen from FIGURE 7C, the voltage-power factor characteristic of the SVL is a good approximation of the voltage-current and voltage-temperature characteristics of the SVL.
[90] As the test voltage increases, current flows from voltage source 1124 through segment 108c to conductor link 818b to segment 108b to link 318a QQbRnn / bznz / q / υιλι of conductor to segment 108a in a manner that gradually increases the voltage across the cable shield segments and the connected SVLs. The voltage at link 318a may be measured locally at link box 1114 by voltage detector 1130a and the voltage at link 818b may be measured by voltage detector 1130b in link box 1115. The voltage-current characteristic of the SVL is non-linear; and as the test voltage increases toward the conduction threshold of the SVL, current of increasing magnitude begins to flow. As the voltage across the SVL moves into the conduction region, the apparent resistance of the SVL decreases and the current through the SVL increases from microamps to milliamps. This increase in SVL current results in an increase in the SVL surface temperature.Therefore, monitoring or measuring the heat dissipated by the SVLs 310a and 810b in the link boxes 1114 and 1115 by means of the detectors 1128a and 1128b, respectively, provides a means for determining the functional reliability of the SVLs.
[91] As previously discussed and graphically shown in FIGURE 7A and FIGURE 7B, the characteristic voltage-temperature (VT) curve for the SVL closely resembles its characteristic voltage-current (VI) curve. Consequently, the heat information produced by detectors 1128a and 1128b are good representations of the current flowing in the SVLs. Likewise, the voltage-power factor curve for the QQfrRnn / frznz / q / υιλι The SVL, shown in FIGURE 7C, is a good representation of the SVL current, as well as the heat dissipated by the SVL. Therefore, in another embodiment, the temperature detector 1128 may be replaced by the power factor detector described above.
[92] As mentioned above, the voltage-current (VI) characteristic or relationship of a typical SVL can usually be found in the technical literature of the SVL manufacturer. A database referencing the VI characteristics of different SVLs, the manufacturers, and the model numbers of those SVLs can be readily created from the literature or by simple laboratory testing of the conduction transition region of the SVLs. In that database, the VI and VT characteristics corresponding to specific SVLs can be stored. When testing the cable shield system schematically illustrated in FIGURE 11, the VI characteristics of SVLs 310a and 810b can be compared to the VI characteristics stored in the database.If the VI characteristics of the SVLs under test correspond (i.e., are highly similar) to the known VI characteristics stored in the database, the SVLs are functionally operable and are recognized as good. However, if the VI characteristics of the SVLs under test differ from the VI characteristics stored in the database, there is a clear indication of a system component failure. QQbRnn / bznz / q / uyl degraded or failed and further diagnosis may be warranted. The cause of the abnormality, which may be a failed SVL, a shorted break gap within the splicing hardware, or a damaged cable jacket, can be determined using data collected from the supplementary detectors in the junction box, other junction boxes in the circuit, and from the voltage and current supplied by test equipment connected to the shield system, e.g., voltage source 1124. Additionally, the voltage source can be connected at other locations on the main sections to avoid dielectric testing of shield breaks and thereby isolate the abnormality to a defective or failed shield break.In this way, the functional reliability of the cable shielding system can be easily and effectively determined, without requiring entry into the access ports and opening the junction boxes within them.
[93] Therefore, the condition of the shielding system is determined to be in a functional condition when the current through the SVL at the supplied test voltage is consistent with the predetermined properties of the SVL's VI characteristic; that is, the test current and voltage exhibit a relationship that conforms to a predetermined reference relationship. Likewise, the condition of the shielding system is determined to be a functional condition. QQfrRnn / frznz / q / υιλι when the SVL heat at the supplied test voltage, as monitored by the temperature detector, is consistent with the predetermined characteristics of the SVL. In other words, the shielding system condition can be determined to be a fault or non-conformance condition when the SVL heat, as monitored by the detectors, is inconsistent with expected behavior.
[94] Embodiments utilizing the present invention may include the shield bonding and grounding configurations described in connection with the schematic illustrations of FIGS. 12-14. FIGS. 12-14 illustrate a cable shield system comprised of a cable segment wherein one end of the cable shield is grounded and the remote ungrounded end is connected to an SVL. FIG. 12 shows single phase (e.g., phase A) conductor cable segments 1204 and 1204' of a three phase high voltage cable joined at splice hardware 1203. The splice hardware may be similar to splice 103 of FIGURE 1. Cable segments 1204 and 1204' are surrounded by shields 1208 and 1208', similar to shields 108 and 108' of FIGURE 1.One end, or point, of the shield 1208 is directly connected to ground and the other is coupled to ground by the SVL 1210 included in the housing 1214, which may be a bonding box, a ground box, or the like, similar to FIGURE 2. In this embodiment, the bonding box 1214 does not. QQfrRnn / frznz / q / υιλι crisscrosses, or cross-joins, shield segment 1208 to shield segment 1208'. Rather, in this embodiment, housing 1214 includes a conductor that connects shield segment 1208' to ground 1213. At its remote end, shield segment 1208' is grounded via SVL 1210' included in housing 1214'. Housing 1214' may be similar to housing 1214 and may include another conductor that connects another shield segment (not shown) to ground as shown in FIGURE 2. Additionally, as shown in FIGURE 12, ground continuity conductor 1225 is installed to provide a path for fault current if and when present. A single ground continuity conductor can be installed for all phases (i.e. phases A, B and C).Due to the relatively close physical separation between the cable phases and the additional separation of the ground continuity conductor, minimal current is induced in the ground continuity conductor and therefore there are no or minimal additional heating losses to account for in high voltage cable ratings.
[95] The cable shield system illustrated in FIGURE 12 is tested, in accordance with the present invention, to evaluate the functional reliability, or operational integrity, of the shield grounding and bonding system, including the installed SVLs. To perform this maintenance test, QQfrRnn / frznz / q / uyl the high voltage conductor 1204, 1204' is de-energized and the shield segment 1208 is isolated from ground by disconnecting from ground the point thereof which is remote from the housing 1214. A voltage source 1224, shown in dashed lines, such as the DC or AC voltage source described above, is connected to that point. It is seen that, as the amplitude of the test voltage supplied by this voltage source increases towards and above the conduction threshold voltage of the SVL 1210, the amplitude of the current flowing through the SVL increases in the manner illustrated in FIGURE 7A and this current flow causes the surface temperature of the SVL to increase as shown in FIGURE 7B. Thus, the increasing current through the SVL correlates well with an increase in surface temperature.An assessment of the SVL condition can be made by monitoring the current flow through the SVL, using a suitable current detector, as the SVL voltage increases; or preferably by using the temperature detector 1228 to monitor the increase in SVL surface temperature as the SVL voltage increases. The latter is a more robust and effective indicator of a fault or abnormal condition in the cable armor system, and in particular in the SVL 1210. The voltage, current, and temperature information obtained during the maintenance test by the voltage detector 1230. QQbRnn / bznz / q / υιλι current detector (not shown) and temperature detector 1228, are used to evaluate the condition of the cable shield bonding and grounding system and, in particular, the functional reliability of the installed SVLs.
[96] Similarly, the shield segment 1208' and the SVL 1210' are tested to evaluate their condition. The de-energized high voltage conductor shield segment 1208' is isolated from ground by disconnecting it from ground 1213 at housing 1214. Then, a voltage source 1224', shown in dashed lines, such as the DC or AC voltage source discussed above, is connected to the isolated shield segment at any accessible location. It is appreciated that there is no need to enter housing 1214 in order to remove the ground potential from segment 1208' as this can be done externally of housing 1214 and sufficient clearances are provided to prevent electrical flashover between energized conductive components, such as shields, and de-energized conductive surfaces or components.In this case, any hardware connected to the shield segment 1208' in the housing 1214, such as metal support structures, will be energized during the test.
[97] As the test voltage supplied from source 1224' to segment 1208' increases, the SVL surface temperature information, from SVL 1210' is acquired QQfrRnn / frznz / q / υιλι by the temperature detector 1228'. The resulting voltage-temperature characteristic of the SVL under test is compared to the voltage-temperature characteristic of a similar functional SVL on file in the database to determine the operational integrity of the SVL 1210'. Thus, a fault or abnormality condition in the cable armor system can be detected simply by comparing the voltage-temperature characteristics of the installed SVLs (e.g., SVL 1210, 1210') with those of a new SVL.
[98] FIGURE 13 and FIGURE 14 are alternate grounding and shield bonding schemes for single-point ground cable shields with ground continuity conductor 1325, 1425. The operation of these alternate schemes is substantially the same as the operation of the cable shield system of FIGURE 12, with different locations of the SVL and ground connections. Nevertheless, during testing, the same procedure discussed above is implemented: de-energize the high voltage cable circuit, isolate the shield segment under test containing the SVL from ground, apply an increasing test voltage, and monitor the SVL surface temperature.
[99] FIGURE 13 illustrates the configuration where single phase segments 1304 and 1304' of a three phase high voltage cable are joined at splice hardware 1303, similar to splice 103 of FIGURE 1. Single phase segments 1308 and 1308' of a three phase high voltage cable are joined at splice hardware 1303, similar to splice 103 of FIGURE 1. Single phase segments 1308 and 1308' of a three phase high voltage cable are joined at splice hardware 1303, similar to splice hardware 13 ... QQfrRnn / frznz / q / υιλι shield of cable segments 1304 and 1304' are substantially the same as shield segments 1208 and 1208' of FIGURE 12. The configuration shown in FIGURE 13 differs from that shown in FIGURE 12 in that shield segment 1308' is coupled to ground potential via SVL 1310' in housing 1314. The other end of segment 1308' that is remote from housing 1314 is grounded.
[100] The cable shield system illustrated in FIGURE 13 is tested by de-energizing the high voltage conductor and isolating (i.e., disconnecting) segments 1308 and 1308' from ground. A voltage source 1324, shown in dashed lines, is connected to the isolated segment 1308 in place of ground, and the test is performed. A separate voltage source 1324' or, alternatively, a test voltage source 1324 is relocated to section 1308', and connected to the isolated segment 1308'. Shield segments 1308 and 1308' and the SVLs 1310, 1310' connected thereto are tested in accordance with the procedure described above. Voltage and temperature information obtained during a test is used to determine the functional reliability of the shield grounding and bonding system.
[101] FIGURE 14 illustrates yet another single point grounding configuration in which single phase segments 1404 and 1404' of a three phase high voltage cable are joined at splice hardware 1403. Segments 1408 and QQfrRnn / frznz / q / υιλι 1408' of shield of cable segments 1404 and 1404' are coupled in common to ground 1413, for example, at or near the location of the splice hardware. Points of the shield segments remote from the common ground connection are coupled to ground by SVLs 1410 and 1410' in housings 1414 and 1414', respectively. FIGURE 14 also illustrates ground continuity 1425 to provide a path for potential fault current.
[102] The cable shield system of FIGURE 14 is tested by de-energizing the high voltage conductor and isolating shield segments 1408 and 1408' by disconnecting the shield segments from ground. A voltage source 1424 similar to the DC or AC voltage source described above, and shown in dashed lines, is connected to the common connection of segments 1408 and 1408' in place of ground 1413. Alternatively, the voltage source may be connected to the isolated shield sections at any access point, including at bonding box 1414 or 1414', and, as mentioned, ground 1413 is disconnected from the shield segments to isolate the shield segments for testing. The shield segments and the SVLs connected thereto are tested in accordance with the procedure described above.The voltage and temperature information of the SVL surface obtained during a test is used to detect a fault or abnormal condition in the shielding system. QQfrRnn / frznz / q / υιλι cable .
[103] Although FIGURE 14 describes a test procedure for testing both segments 1408 and 1408', as well as both SVLs 1410 and 14107, simultaneously, it will be appreciated that, if desired, sections 1408 and 1408' may be tested independently.
[104] The above discussion applies to bonding box applications associated with single point and cross bonded grounded cable shields. In practice, various single point and cross bonded grounding configurations may be encountered along the circuit route, such as where the circuit is comprised of more than three cable sections due to practical length maximums. It is not uncommon to encounter a high voltage cable circuit 4 miles (6.437 km) in length. With practical cable lengths typically on the order of 2000 feet (609.6 meters), such circuits may include a plurality of primary cross bonded sections, each comprised of three secondary sections between a common ground point, as described above and as schematically illustrated in FIGURE 15. The test arrangement discussed above may be applied to any number of sections as now described.
[105] The configuration shown in FIGURE 15 is similar QQfrRnn / frznz / q / uyl to that shown in FIGURE 11, but FIGURE 15 illustrates six cable segments utilizing two additional cross-bond boxes 1514 and 1515 and a central ground box 1536. This configuration accommodates a circuit length twice that of the configuration of FIGURE 11 by coupling one cross-bonded circuit arrangement to another. Here, the point at which the shield segment 108c is connected to electrical ground is through the ground box 1536 which may be located in a manhole. As shown, a connector link 1537 within the ground box physically connects the segment 108c to ground. Alternatively, the ground box 1536 may be omitted and the respective shield bond wires may be connected directly to ground.
[106] Grounding box 1536 also includes another connector link 1538 that physically connects a shield segment 1508c of high voltage cable 104c to electrical ground. Segment 1508c is similar to segment 108c and is, for example, the phase C shield of high voltage conductor 104c. In FIG. 15, segment 1508c is coupled to phase B segment 1508b of conductor 104b via connector link 1518b included in link box 1515. Link box 1515 is similar to link box 1115 and includes an SVL 1510b, similar to SVL 1510b, and a detector 1528b, similar to detector 1128b in link box 1115. The 1515 link box also includes a 1530b voltage detector, similar to the QQfrRnn / frznz / q / uyl voltage detector 1130b in FIG. 11, adapted to detect voltage across SVL 1510b. In a similar manner, tie box 1514 includes a connector tie 1518a that electrically connects phase B segment 1508b of high voltage conductor 104b to phase A segment 1508a of high voltage conductor 104a. Tie box 1514 is similar to tie box 1114 and includes an SVL 1510a, similar to SVL 1510a, and a detector 1528a, similar to detector 1128a in tie box 1114. The link box 1514 also includes a voltage detector 1530a, similar to the voltage detector 1130a in FIG. 11, adapted to detect the voltage across the SVL 1510a. The outer ends of the phase A shield segments 108a and 1508a, remote from the link boxes 1114 and 1514, respectively, are electrically grounded during normal operation.
[107] The manner in which the cable shield system shown in FIGURE 15 is tested in accordance with the present invention is schematically illustrated in FIGURE 16. When testing the cable shield system of FIGURE 15, the physical electrical ground connection at the point along the circuit length of the remote segment 108a of the tie box 1114 is disconnected from ground, as is the point along the circuit length of the remote segment 1508a of the tie box 1514, thereby isolating the segments 108a and 1508a from ground. Additionally, the tie box 1536 is connected to the ground. QQfrRnn / frznz / q / uιλι ground, which during normal operation connects segments 108c and 1508c to ground, is also disconnected from ground to effectively isolate the electrically connected shield segments in link boxes 1114, 1115, 1514 and 1515 from ground, as shown at 1626. There may be no need to open housing 1536 in order to remove ground from connector links 1537 and 1538 because this can be done externally of the housing. In this embodiment, connector links 1537 and 1538 are not ordinarily connected to other shield segments that can be grounded externally of housing 1536.
[108] In this manner, segments 108c and 1508c are electrically isolated from ground. Similar to the test setup previously described in connection with FIGURE 11, the cable shield system of FIGURE 16 may be tested from any convenient point. The test voltage is supplied by a voltage source 1624, which may be a DC source or an AC source similar to the voltage source 1124 of FIGURE 11, shown here as connected at the terminal end of segment 108a. The test voltage is supplied with a gradually increasing amplitude to the electrically isolated end of segment 108a. The amplitude of the test voltage may be increased gradually in predetermined steps; or alternatively, as a linearly increasing voltage. QQfrRnn / frznz / q / υιλι
[109] Similar to the test configuration of FIGURE 11, as the test voltage supplied by the voltage source 1624 increases, the voltage at segment 108a, conductor link 318a, SVL 310a, segment 108b, conductor link 818b, segment 108c, conductor links 1537 and 1538, segment 1508c, conductor link 1518b, segment 1508b, conductor link 1518a, and finally segment 1508a also increases. As the test voltage increases above the conduction threshold of the SVLs, a current of increasing magnitude flows through the SVLs when the SVLs operate above the conduction threshold region. As represented by the SVL VI characteristic of FIGURE 7A, when the supplied test voltage exceeds the predetermined conduction threshold voltages of the SVL, the current through that SVL increases disproportionately.The heat dissipated by each SVL is related to the current flowing through it; and detecting this heat is a good approximation of the SVL current. Heat detectors 1128a and 1128b, which may be IR detectors, detect the heat dissipated by SVLs 310a and 810b, and detectors 1528a and 1528b detect the heat dissipated by SVLs 1510a and 1510b. The signals produced by the heat detectors thus constitute information representing the current flowing through the SVLs. The voltages across the SVLs are detected by voltage detectors 1130a, 1130b, 1530a, 1530b. QQfrRnn / frznz / q / υιλι produce information representing the voltages across the SVLs. This voltage and heat (representative of current) information is acquired to evaluate the functional reliability of the cable shielding system. The voltage source 1624 can be applied separately and sequentially to each insulated section while the other sections are grounded.
[110] FIGURE 17 is a schematic block diagram of a remote monitoring system for evaluating the functional reliability of a cable armor system of the type discussed above, utilizing the cross-bonding configuration illustrated in FIGURE 5, and including a junction box detector package, including the detectors of, for example, FIGURE 11, and environmental detectors. Voltages VA, VB, and VC represent the voltages across SVLs 1710a, 1710b, and 1710c detected by voltage detectors 1730a, 1730b, and 1730c, respectively. These voltage detectors may be similar to voltage detectors 1130a and 1130b of FIGURE 11. FIGURE 17 also shows currents IA, IB, and IC flowing through the connector links, as detected by respective current detectors 1732a, 1732b, and 1732c. The current detectors may be similar to current detector 440a of FIGURE 4A.FIGURE 17 also represents the surface temperatures Ta, Tb, and Te of SVLs 1710a, 1710b, and 1710c, as detected by the detectors. QQfrRnn / frznz / q / υιλι 6 1728a, 1728b, and 1728c, respectively. Block 1734 represents internal environmental sensors for monitoring environmental conditions within the junction box enclosure, such as ambient temperature, pressure, and humidity within the housing. Other environmental conditions may also be monitored, as is known to those skilled in the art.
[111] The voltages VA, VB, and VC represent the voltages that are sensed or monitored across the SVLs. These voltages may be monitored periodically during normal in-service operation. Consistent with the present invention, the voltages across the SVLs may be continuously monitored during out-of-service maintenance testing of the cable armor system. As discussed above in connection with FIG. 11, the voltage detectors 1730 may comprise a resistive divider to reduce higher voltages that are intentionally introduced during a maintenance test, as well as high voltages that could occur in service as a result of faults and overvoltages. The resistive dividers reduce such SVL voltages to levels suitable for processing circuitry, such as microprocessors. These overvoltage events should not cause monitoring circuitry, including the detectors, to fail.Currents IA, IB and IC represent the current flowing in each conductor link in the configuration. QQfrRnn / frznz / q / υιλι cross-linked shield shown in FIGURE 11.
[112] The SVL surface temperatures Ta, Tb, and Te are sensed by temperature detectors 1728a, 1728b, and 1728c and may be periodically monitored during normal in-service operation of the high voltage cable. Consistent with the present invention, the SVL surface temperatures are sensed during out-of-service maintenance testing. In one embodiment, the temperature detectors may be turned on or activated from their inactive states in response to a command, such as a data request, from processing circuitry. Alternatively, the temperature detectors may be activated in response to signals generated by, or in response to, the voltage detectors and the current detectors to detect and record changes in SVL surface temperatures that occur during transient events when such sensed voltage and / or current exceeds a predetermined level.
[113] Environmental conditions, such as ambient temperature, pressure, and humidity, existing within the enclosure housing are also monitored by detectors to detect and monitor water ingress and high housing temperatures which may be indicative of faulty seals and loose internal connections. The ambient temperature within the housing also provides a QQfrRnn / frznz / q / υιλι reference with which the temperature increase of the SVL surface can be compared.
[114] In one embodiment, signals produced by the detectors, for example, current, voltage, temperature, pressure, and humidity signals, are sent, via a wire, to a controller, referred to as a link box controller 1735, such as a microprocessor or other processing circuitry. The link box controller may store instructions, for example, for acquiring detector information from the detectors at scheduled times. A store may also be provided on or near the controller for storing the detector data. The detector data may be stored in its original form, as received from the detectors, or reduced (e.g., compressed, such as statistically compressed) to conserve storage space. The link box housing may also house a battery that provides electrical power to the link box controller and the detectors.Data compression of the detector data serves to conserve battery life. In a preferred embodiment, the detector data from the gateway controller is transmitted wirelessly to a remote central location, for example, via a low-power wide area network (LP-WAN) communications protocol. In another embodiment, the detector data is transmitted via. QQbRnn / bznz / q / υιλι QQfrRnn / frznz / q / υιλι a fiber optic cable to the remote location.
[115] In another embodiment, a remote monitoring device controller 1736 may be used as a control and communications interface between the gateway and a central server. In one embodiment, the remote monitoring device controller includes a low power wide area network (LP-WAN) transmitter for wirelessly transmitting detector information to the remote processing circuitry 1738. An example of a suitable low power wide area network is described in U.S. Patent 10,607,475. The gateway controller 1735 and the remote monitoring device controller 1736 may be located in the same manhole.Alternatively, the remote monitoring device controller 1736 may be arranged at a location separate from the junction box location, such as at another underground location, to which detector information is supplied from the junction box controller 1735.
[116] Preferably, the link box controller 1735 responds to instructions receiveable from the remote processing circuitry 1738 periodically or from time to time to measure, calculate, compare, store, and transmit detector information such as SVL voltage, current, and temperature information, as well as environmental information, stored in the link box controller. It is appreciated that the received instructions seek to balance the competing need for data used to evaluate the condition of the cable shield system (i.e., to send the data when needed) with battery consumption, especially during data transmission intervals.
[117] In yet another embodiment, processing circuitry included in the link box controller 1735 provides local processing and storage of acquired detector data, including voltage, current, and temperature, to provide a historical database for comparison with recently acquired data as a routine on-board check to detect significant abnormalities that trigger notifications.
[118] Detector data can be uploaded to a central server operable to compile data from other bonding boxes on the same cable circuit from which operational abnormalities that are difficult to identify locally can be determined, thus allowing assessment of the integrity of the circuit's shield bonding and grounding system. For example, during normal operation, the current flowing in each of the bonded cable shield segments of a cross-bonded system will be the same. But any deviation would suggest an unwanted current path or a fault in the circuit.
[119] The testing procedure discussed above QQfrRnn / frznz / q / υιλι can be automated with the voltage and surface temperature of the SVL fed back to processing circuitry which controls the rate of voltage rise or fall to account for detected surface temperature changes for each of the SVLs. It will be appreciated that, following the increase in test voltage supplied by the voltage source discussed above, the voltage should be decreased to allow the SVLs to cool over time. The automation feedback control shortens the test period by allowing higher initial rates of voltage rise which can be decreased as the test voltage approaches the SVL conduction threshold, thereby preventing amplitude over-regulation and facilitating greater repeatability of the measurement of the voltage-temperature characteristic in the conduction transition region.Advantageously, temperature measurements from the detectors transmitted to the processing circuitry can be sent to test technicians in the field via computer connections or cell phone communication in near real time.
[120] By detecting the temperature of the SVL and knowing the test voltage, the condition of the SVL, cable jacket, grounding system, and breakaway gaps in the splicing hardware are easily detected to anticipate potential problems. For example; by supplying a QQfrRnn / frznz / q / υιλι variable DC test voltage to the cable armor system from the cable ends (at substations), the operability of the SVL is determined by detecting the temperature rise of the SVL as a function of the test voltage as the SVL current passes through the conduction threshold region. Consequently, maintenance tests of the cable armor system are obtained that do not require manhole entry, disconnecting cable bonding wires, or opening bonding boxes or other enclosures to remove bonds for testing and maintenance.
[121] Some practical diagnostics are derived from the present invention. For example, when the test voltage supplied to the SVL is below its conduction threshold and there is little or no heat dissipated by the SVL, but the SVL dissipates measurable heat when the test voltage exceeds the SVL's conduction threshold, the clearance, jacket, SVL, and ground connections are determined to be in an acceptable operating condition and no maintenance is required.
[122] On the other hand, if no heat is detected from the SVL when the test voltage is above the SVL conduction threshold voltage, it can be determined that the interruption gap and sleeve are functioning properly, but there is most likely a problem with the SVL or the associated ground connections. However, if significant heat is detected being dissipated by the SVL when the test voltage is above the SVL conduction threshold voltage, it can be determined that the interruption gap and sleeve are functioning properly, but there is most likely a problem with the SVL or the associated ground connections. QQfrRnn / frznz / q / υιλι test voltage is below the SVL conduction threshold voltage, the condition of the break and sleeve clearance is most likely appropriate; but the SVL may be damaged or shorted, or an inadequate SVL is present.
[123] As another example, if the current supplied by the test voltage source is at its maximum, but the voltage across the SVL nevertheless does not reach or exceed the SVL conduction voltage and no heat is detected at the SVL surface, it is most likely that the interrupt gap or cable jacket is causing unexpected loading of the test circuitry and a short circuit is suspected.
[124] These examples are described in more detail below, together with FIGURE 18, which is a schematic illustration of tests carried out on a main section of high voltage cable.
[125] In the embodiment of FIGURE 17, the gateway controller 1735 may record (e.g., simply store) the detector signals, but not transmit the detector data unless triggered by a detector input exceeding a predetermined level, e.g., voltage data exceeding a preset level. Such events differ from normal operation and are recognized as unscheduled data transmission events.
[126] Recent history (e.g., several weeks) QQfrRnn / frznz / q / υιλι of the voltage, current, temperature, and environmental information may be stored on board in the link box controller, but long-term history may be stored remotely, such as in remote processing circuitry 1738, to represent the behavior of the high voltage power cable circuit and may be used to establish control, notification, and alarm points that are consistent with that long-term behavior. A database of such information may include many parameters including specific details of the SVLs being monitored, such as manufacturing history and ratings.
[127] Thus, it is seen that the present invention provides system operators with a means and method for evaluating the functional reliability of the shield bonding and grounding system of high voltage power cable circuits. The invention utilizes an array of detectors to collect data at remote locations, namely, manholes, and transmit this information in near real time to a central server where it can be accessed to evaluate the electrical and environmental operating conditions of the cable shield system. This information can be acquired when the cable circuit is out of service and subjected to the test protocol described herein.
[128] Turning now to FIGURE 18, where the reference numerals used in FIGURES 1 and 11 are used to QQbRnn / bznz / q / υιλι identify similar components, the test voltage source 1124 is coupled to the cable shield segment 108a and the shield segments 108'b and 108'c are grounded, just as at their circuit ends. Although not shown, a conventional current meter, similar to the current detector 440 described above, is coupled to the output of the voltage source to provide a measure of the current supplied to the cable shield segments by the voltage source. Connector link 318a in link box 1114 cross-connects phase A shield segment 108a to phase B shield segment 108b and connector link 818b in link box 1115 cross-connects shield segment 108b to phase C shield segment 108c. These are the shield segments to be subjected to the test voltage.The bonding box 1114 may be of the type shown as the bonding box 314 in FIG. 3 (or FIG. 5). Also in the bonding box 1114, the connector bond 318b cross-connects the phase B shield segment 108'b to the phase C shield segment 108'c; and the connector bond 318c, also in the bonding box 1114, cross-connects the phase C shield segment 108'c to the phase A shield segment 108'a. FIG. 18 also illustrates the shield break gap 118a, present in the splicing hardware that electrically isolates the shield segment 108a from the phase A shield segment 108'a, the shield break gap 118b. QQfrRnn / frznz / q / υιλι shield present on the splice hardware that isolates the shield segment 108b from the phase B shield segment 108'b, and the shield interruption separation break 18c present on the splice hardware that isolates the shield segment 108c from the phase C shield segment 108'c.
[129] Because voltage source 1124 is connected to shield segment 108a and shield segment 108'c is grounded, the voltage Vgap across interruption gap 118a, in the absence of abnormalities, should equal the test voltage Vtest supplied by the voltage source. Likewise, connector link 318a in link housing 1114 couples the voltage Vtest on shield segment 108a to shield segment 108b, while segment 108'b is grounded, resulting in the voltage Vgap across interruption gap 118b, in the absence of abnormalities, equal to the test voltage Vtest supplied by the voltage source. The connector link 318b in the link housing 1114 couples the ground potential to the shield segment 108''c and, as mentioned, the shield segment 108'c is grounded, resulting in the voltage Vgap across the gap 118c of Vgap=0.It is appreciated that as a result of the connector links in the link box 1115 coupling the shield segment 108''c which is at ground potential to the shield segment 108''a, the resulting potential at the Vgap interruption gap isolating the. QQfrRnn / frznz / q / υιλι shield segment 108'a of shield segment 108''a shall be zero. Additionally, in the absence of abnormalities, the potential appearing at the break gap 118b isolating the shield segment 108b from the shield segment 108'b and also the potential appearing at the break gap 118c isolating the shield segment 108'c from the shield segment 108''c shall be Vtest.
[130] As illustrated in FIGURE 18, a test whereby one connected group of three shield segments, e.g., shield segments 108a, 108b, 108c, is isolated is tested with the remaining three segment groups, shield segments 108'b, 108''c, 108''a and shield segments 108'c, 108'a, 108''b, grounded provides a functional test of the cable jackets, shield breaks, and SVLs associated with those isolated segments. The test procedure is repeated two additional times, to isolate shield segments 108'b, 108''c, 108''a and to isolate shield segments 108'c, 108'a, 108''b, with the unisolated shield segments grounded.
[131] As described above, an SVL, a temperature detector, and a voltage detector are included within each junction box. Junction box 1114 is representative, and as shown, junction box 1114 contains SVL 310a (illustrated as a variable resistor), temperature detector 1128a, and voltage detector 1130a. Substantially, the QQfrRnn / frznz / q / υιλι The same components are associated with the other cross-linked shield segments in the link box 1114 and in the other link box, such as the link box 1115. Six examples of possible test results will now be described. However, it should be understood that the present invention is not limited to these examples only and that the test procedure described herein may be used for other examples of functionality.
[132] Example 1: Shield segments 108'b and 108'c are grounded and a test voltage is supplied to shield segment 108a by voltage source 1124. The voltage appearing across SVL 310a is measured in the junction box by voltage detector 1130a. The test voltage level is stepped up to a level Vthresh-, which is just below the conduction threshold voltage of SVL 310a. This voltage appears across the cable jacket (the cable jacket impedance is identified in FIGURE 18 as resistance Rj), the gaps (Vgap), and the SVLs associated with (i.e., coupled to) shield segments 108a, 108b, and 108c. Consequently, the cable jacket, break gaps and SVLs are subjected to a dielectric withstand voltage test at this test voltage Vthresh- level for a specified period of time.At this voltage level, the SVLs do not conduct; and the apparent resistance of each SVL is very high. The current. The resulting QQfrRnn / frznz / q / uylI across the SVL is very small and is not expected to cause heating of the SVL. Here, the temperature detector does not detect significant temperature, i.e., the temperature detector 1128a detects ambient temperature. Assuming that the detected SVL voltage Vsvl is substantially equal to the test voltage Vthresh- and no temperature rise is detected at the SVL surface, the results of this first test example suggest that the cable jacket and interruption gap are functionally operational and that the SVL is not shorted and has not prematurely entered its conduction transition region. Confirmation of the SVL's functionality can be obtained by an additional test described below in Example 2.
[133] Example 2: The test procedure of Example 1 is followed, but with a higher test voltage to drive the SVL into its conduction transition region, demonstrating that the SVL is functional. In Example 2, the test voltage supplied by voltage source 1124 is increased to a level Vthresh+ that is just above the SVL conduction threshold voltage of SVL 310a. As in Example 1, shield segments 108'b and 108'c are grounded. At this voltage Vthresha, the apparent resistance of a properly functioning SVL decreases, thus drawing sufficient current from test source 1124 to cause heating. QQfrRnn / frznz / q / υιλι of the SVL, resulting in an increase in surface temperature which is detected by temperature detector 1128. Because a higher current is drawn from the test source supplying a test voltage above the conduction threshold voltage and the surface temperature of the SVL is above ambient, it can be concluded that the SVL is operating properly and that there is no fault or defect in the interruption gap 118a or the cable jacket.
[134] Example 3: Shield segments 108'b and 108'c are grounded and the test voltage supplied to shield segment 108a by voltage source 1124 is increased to the Vthresh- level, just below the conduction threshold voltage of SVL 310a, as in Example 1. If the output current of the voltage source (as measured by the current meter, not shown) is much higher than would be expected by an SVL operating below its conduction threshold voltage Vthresh and the voltage detector in the link box detects the voltage across the SVL to be substantially equal to the test voltage Vthresh level and the surface temperature of the SVL is detected at, but not above ambient, this is indicative of a low resistance path to ground external to the SVL. This strongly suggests that the high voltage source current is caused by a defect in the jacket or the interruption gap. QQfrRnn / frznz / q / υιλι
[135] Example 4: Shield segments 108a, 108'b and 108'c are all insulated from ground and connected in common; and the test voltage from source 1124, in this case Vthresh, is supplied to the segments connected in common. As a result of all shield segments being at the same voltage, the voltage Vgap across all interruption gaps 118a, 118b, 118c and also the voltage appearing across interruption gaps 118'a, 118'b, 118'c is zero. Because no current flows across the interruption gaps, if no indication of a rise in SVL surface temperature is detected, similar to that in Example 3, but excessive current is drawn from voltage source 1124, a jacket defect is most likely present.Alternatively, if the current drawn from source 1124 is consistent with that expected from a functional shield system, for example, below the level where the SVL conducts (Ithresh-), the defect is probably associated with one of the interruption gaps.
[136] Example 5: In the process of performing a test in accordance with Example 1, while raising the test voltage to Vthresh-, the current I is larger than expected for the voltage appearing across the SVL in the junction box, i.e., the voltage across the SVL is Vthresh- (significantly below the threshold voltage of QQfrRnn / frznz / q / υιλι conduction), and the current is Ithresh or higher, and the SVL surface temperature is detected to be above the ambient temperature of the junction box. This suggests premature conduction of the SVL, indicative of a damaged SVL or possibly an undersized SVL being installed.
[137] Example 6: In the process of performing the test in Example 2 while raising the test voltage to Vthresh++, significantly above the conduction threshold voltage of the SVL, the current I is much lower than expected for the voltage appearing across the SVL at the junction box (e.g., I <Ithresh--) y la temperatura de la superficie del SVL es sustancialmente igual a la temperatura ambiente en la caja de enlace. Esto sugiere que se ha instalado un SVL dañado o inadecuadamente dimensionado.
[138] In this way, it is appreciated that the installed detectors, test procedures and diagnostics can be used not only to evaluate the overall functionality of the cable shielding system but also to isolate and locate defective or damaged components. The above examples are summarized in the following table: QQfrRnn / frznz / q / υιλι Possible Example______Vsowce__________Vgap____________1___________V.SVL__________1 svl_________anomaly 1 Vrhrcsh(-) Vlhrcsh(-) Illircshl-) V Thrcshí-) TAmbicnt None apparent 2 Vllircsh(-) Vthrcsh I'rhrcsh(+) Vthrcsh TAmbicnt(-) 3 VrhrCsh(.) Vrhrcsh(-) Iriircsh(+) V'rhfcsh(-) TAmbicnt Sleeve or break clearance 4* VThrcsh(-) 0 iThrcshold(-) Vlliicshl -) TAmbicnt Sleeve VThrcsh(-) 0 ItIhcsIi(-) Vnircsh(-) TAmbicnt Break clearance 5 V i hrcsh(-) V Thrcshl--) 11 hrcsh Vriucsh(-) Tambicnt(-) SVL 6 V'Hircshí—) Vrhrcshl—) Iriircshí-> Vlhrcsh(—) TAmbicnt SVL - - Far below - Just below + Just above ++ Far above * Shield segments 108a, 108'b and 108'c connected in common
[139] While the present invention has been shown and described with reference to preferred embodiments, it should be understood that this invention is not limited to those precise embodiments. One skilled in the art may make other modifications and variations in form and details without departing from the spirit and scope of the invention as defined in the appended claims.
Claims
1. A method for testing the functional reliability of a cable shield system for a high voltage cable circuit comprised of at least one segment along a cable route, the cable shield system including at least one segment of a conductive shield concentrically surrounding a phase of a corresponding segment of the high voltage cable, the conductive shield extending along a length of the circuit and being physically connected to electrical ground during normal operation at least at one point along the length of the circuit, the conductive shield being connected at least at one ungrounded point by means of a connector bond within a covered enclosure through a shield voltage limiter (SVL) to ground, the method comprising: electrically isolating a segment of the conductive shield from ground along the length of the circuit;supplying a test voltage of gradually increasing amplitude to the SVL; monitoring the voltage across the SVL and the current through the SVL in response to the supplied test voltage; and determining the functional reliability of the cable shield system as a function of the monitored voltage across and the current through the SVL. QQfrRnn / frznz / q / υιλι; 2. The method of claim 1, wherein the voltage across and the current through the SVL are monitored by detectors in the enclosure.
3. The method of claim 1, wherein the enclosure includes a heat detector arranged to detect heat dissipated by the SVL; and wherein the current flowing through the SVL is represented by detecting the dissipated heat.
4. The method of claim 1, wherein the functional reliability of the cable shielding system is determined at a remote location of the enclosure by transmitting to the remote location information representing the voltage across and the current through the SVL.
5. The method of claim 4, wherein the information representing the current through the SVL comprises heat information representing the detected heat dissipated by the SVL.
6. The method of claim 1, wherein the covered enclosure is a junction box housing containing connector links for physically connecting the conductive shield of a respective phase of the high voltage cable to the conductive shield of a different phase and to a respective SVL; and wherein the step of electrically isolating a segment of the conductive shield from ground comprises disconnecting the conductive shield from ground at all points of the segment of the cable shield section being tested.
7. The method of claim 6, wherein the cable shield system includes a first junction box in which the conductive shield of a first phase of the high voltage cable is electrically connected to the conductive shield of a second phase of the high voltage cable, and a second junction box in which the conductive shield of the second phase of the high voltage cable is electrically connected to the conductive shield of a third phase of the high voltage cable and wherein a point of the conductive shield of the first phase of the high voltage cable remote from the first junction box is physically connected to electrical ground during normal operation and a point of the conductive shield of the third phase of the high voltage cable remote from the second junction box is physically connected to electrical ground during normal operation;and wherein the step of electrically isolating a segment of the conductive shield from ground comprises disconnecting the distant points of the conductive shield from the first and third phases of the high voltage cable from ground.; 8. The method of claim 7, wherein the step of supplying a test voltage to one end of the shield segment that has been isolated from ground comprises supplying a gradually increasing DC voltage to the end of the shield segment that has been isolated from ground.
9. The method of claim 7, wherein the step of supplying a test voltage to one end of the shield segment that has been isolated from ground comprises supplying a gradually increasing AC voltage to the end of the shield segment that has been isolated from ground.
10. The method of claim 9, wherein the current through the SVL exhibits a phase shift relative to the voltage across the SVL; and the step of monitoring the current through the SVL comprises monitoring the phase shift of the current relative to the voltage across the SVL.
11. The method of claim 10, wherein the phase shift of the current through the SVL relative to the voltage across the SVL is related to the power factor exhibited by the SVL, and the monitored phase shift is indicative of the functional reliability of the SVL.
12. The method of claim 4, wherein wireless transmission is used to transmit voltage and current information to the remote location from the enclosure.
13. The method of claim 12, wherein the wireless transmission comprises a low power wide area network (LP-WAN).
14. The method of claim 4, wherein a fiber optic cable is used to transmit voltage and current information to the remote location from the enclosure.
15. The method of claim 12, further comprising storing, in a store disposed at or near the enclosure, information representing voltage across the SVL and heat information representing detected heat dissipated by the SVL; and transmitting the stored voltage and heat information over the LP-WAN in response to instructions received from the remote location.
16. The method of claim 4, wherein the functional reliability of the cable shield system is determined to be a functional condition when the current through the SVL at the voltage across the SVL is consistent with predetermined characteristic properties of the SVL.
17. The method of claim 5, wherein the functional reliability of the cable shield system is determined to be a functional condition when the SVL heat information in the voltage across the SVL is consistent with predetermined characteristics of the SVL.
18. An evaluation system for testing the functional reliability of a cable shield system for a high voltage cable circuit comprised of at least one segment along a cable route, the cable shield system including at least one segment of a conductive shield concentrically surrounding a phase of a corresponding segment of the high voltage cable, the conductive shield extending along a length of the circuit and being physically connected to electrical ground during normal operation at at least one point along the length of the circuit, the conductive shield connecting to a bonding box including a bonding link for electrically connecting the shield of a phase of the high voltage cable through a shield voltage limiter (SVL) to ground, the evaluation system comprising: a voltage source for providing, during a test,a test voltage of gradually or stepwise increasing amplitude; a connector for supplying the test voltage from the voltage source to one end of the shield segment remote from the junction box and isolated from ground, thereby supplying a voltage across the SVL; at least one detector disposed within the junction box for providing information representing the voltage across and current flowing in the SVL in response to the test voltage; a transmitter for transmitting detector information to a location remote from the junction box; and a processor supplied with detector information from the junction box acquired during testing for determining the functional reliability of the cable shield system as a function of the voltage and current information.
19. The evaluation system of claim 18, wherein the current increases through the SVL disproportionately when the voltage across the SVL exceeds a conduction voltage threshold.
20. The evaluation system of claim 18, wherein the at least one detector includes a heat detector arranged to detect heat dissipated by the SVL; and the current information is represented by the detected heat.
21. The evaluation system of claim 18, wherein the voltage source provides a gradually increasing DC voltage to the isolated shield segment.
22. The evaluation system of claim 18, wherein the voltage source provides a gradually increasing AC voltage to the isolated shield segment.
23. The evaluation system of claim 22, wherein the current through the SVL exhibits a phase shift relative to the voltage across the SVL; and the detectors include circuitry for detecting the phase shift of the current relative to the voltage across the SVL as an indication of the functional reliability of the SVL.
24. The evaluation system of claim 18, wherein the transmitter comprises a wireless transmitter.
25. The evaluation system of claim 24, wherein the wireless transmitter comprises a low power wide area network (LP-WAN).
26. The evaluation system of claim 18, wherein the transmitter comprises a fiber optic transmitter.
27. The evaluation system of claim 24, further comprising a storage arranged at or near the link box for storing the voltage and detector information, and wherein the transmitter wirelessly transmits the voltage and detector information.
28. The evaluation system of claim 18, wherein the processor determines a functional condition of the shielding system when detector information on the voltage across the SVL is consistent with predetermined characteristic properties of the SVL.
29. The evaluation system of claim 18, wherein the processor determines a non-functional condition of the shielding system when the detector information is less than a predetermined amount when the voltage across the SVL exceeds the conduction voltage threshold.
30. The evaluation system of claim 20, wherein the processor determines a non-compliance condition of the shielding system when the detected heat is greater than a predetermined amount when the voltage across the SVL QQfrRnn / frznz / q / υιλι is less than the conduction voltage threshold.