Method for detecting series resistance faults in digital electrical transmission systems

Abstract

In a digital electrical power system, current samples are taken along with voltage samples during time windows during which current and voltage are substantially unchanged. A transmission line series voltage is derived from the difference between the transmitter voltage and the receiver voltage. Each transmission line series voltage is divided by the corresponding stored current sample to generate a ratio indicative of the transmission line series resistance. These steps are repeated, and if the difference in the generated ratios for one or more time periods exceeds a predetermined maximum value, the transmitter disconnect device becomes non-conductive; exceeding the predetermined maximum value indicates a series resistance fault. Alternatively, the series resistance, determined by dividing the change in voltage by the change in current, is evaluated to detect a fault.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a safety protection device for an electrical power distribution system, e.g., an electrical power distribution system with electronic monitoring that detects and disconnects power in the event of an electrical fault or safety hazard, particularly when the power transmission line is consuming abnormally high power losses, often referred to as a "resistive fault" or "in-line fault." More particularly, the present invention may be used in digital electrical transmission systems. The present invention is applicable to electrical power distribution in general, illustratively in, for example, electric vehicle charging, communications, or alternative energy power systems. [Background technology]

[0002] background Digital power, or digital electricity, can be characterized as any form of power in which power is distributed in discrete, controllable units of energy. Packet Energy Transfer (PET) is a new type of digital power protocol disclosed in U.S. Patent No. 8,068,937, U.S. Patent No. 8,781,637 (Eaves' 637), and International Patent Application No. PCT / US2017 / 016870, filed February 7, 2017.

[0003] The primary distinguishing factor in digital power transmission systems compared to traditional analog power systems is that electrical energy is separated into discrete units, and each unit of energy can be associated with analog and / or digital information that can be used to optimize safety, efficiency, resiliency, control, or routing. Because energy in PET systems is transferred in discrete quantities, or quanta, it can be referred to as "digital power" or "digital electricity."

[0004] As described in Eaves '637, a source controller and a load controller are connected by a power transmission line. The source controller in Eaves '637 periodically isolates (disconnects) the power transmission line from the power source and analyzes the voltage characteristics present at the source controller terminals at least immediately before and after the line is isolated. The period during which the power line is isolated is referred to by Eaves '637 as the "sample period," and the period during which the source is connected is referred to as the "transfer period." The rate of rise and decay of the voltage on the line before, during, and after the sample period indicates whether a fault condition exists on the power transmission line. Measurable faults include, but are not limited to, a short circuit, high line resistance, or the presence of a person inappropriately touching the transmission line.

[0005] Eaves '637 also describes digital information that can be transmitted between the source controller and the load controller over the power transmission lines to further enhance safety or to provide general characteristics of the energy transfer, such as total energy or voltage at the load control terminals. One method for communicating over the same digital power transmission lines used for electrical power was further described and improved upon in U.S. Patent No. 9,184,795 (Eaves Communication Patent).

[0006] US Patent Application Publication No. 2016 / 0134331A1 (Eaves Power Elements) describes packaging the source-side components of Eaves'637 in various configurations into a device called a digital power transmitter.

[0007] US Patent No. 9,419,436 (Eaves Receiver Patent) describes packaging various configurations of the load side components of Eaves'637 into devices called digital power receivers.

[0008] U.S. Patent Application Publication No. 2018 / 0313886A1 (Mlyniec Line Integrity) describes a method for verifying that voltage measurements at the transmitter side of a system meet minimum integrity requirements in an electrically noisy environment where the specific transmission line characteristics are unknown.

[0009] The method described herein builds on Eaves' 637 and Mlyniec's previous work on Line Integrity, which focused on novel methods for ensuring accurate detection of what Eaves' 637 described as "in-line" faults. In the electrical industry, the term "resistive fault" is often used interchangeably with "in-line" faults. An in-line fault is defined as a fault that causes excessive power loss in the transmission line between a source device and a load device. For example, a loose terminal can result in high connection resistance. High resistance can result in heating, which can lead to fires. In-line faults are one of the leading causes of electrical fires in the electrical distribution industry. Column 3 of Eaves' 637 describes a method for comparing the transmission line voltage at the transmitter side with the transmission line voltage measured by a receiver at the receiver side of the transmission line. The difference in voltage, combined with a known value of current, can be used to determine the in-line power loss value.

[0010] However, practical considerations regarding sensor accuracy, electrical noise, and faulty wiring make it advantageous to derive a method for validating receiver voltage measurements. This specification provides a method for a transmitter to obtain a valid measurement of the transmission line voltage sampled by the receiver and to verify the measurement without interrupting the normal transfer of electrical energy under a Packet Energy Transfer (PET) protocol. Summary of the Invention [Means for solving the problem]

[0011] overview Methods for obtaining transmission line voltage measurements from a receiver, for verifying the integrity of the measurements through comparison with transmitter-side measurements, and for fault detection are described herein, and various embodiments of methods and apparatus for carrying out the methods may include some or all of the elements, features, and steps described below.

[0012] In a digital electrical power system including at least one transmitter, each transmitter monitors and controls the voltage of a respective transmission line and interacts with one or more receivers connected at the opposite end of each transmission line. The transmission line voltage measurements are verified by taking a series of transmission line voltage measurements during a sample period when the transmitter disconnect device is in a non-conducting state. A numerical analysis is performed on the transmitter voltage measurements to determine when the AC component in the transmission line decreases and when the primary change in the transmission line voltage measurement is due to DC decay, and a first voltage measurement taken at that time is stored. A receiver is used to take a series of receiver voltage measurements during the same sample period, and a numerical analysis is performed on the receiver voltage measurements to determine when the AC component decreases and when the primary change in the transmission line voltage measurement is due to DC decay, and a second voltage measurement taken at that time is stored. A calculated difference resulting from subtracting the first stored voltage measurement from the second stored voltage measurement is stored, and if the absolute value of the calculated difference is greater than a predetermined maximum value, the transmitter disconnect device is in a non-conductive state and the transmission line voltage measurement cannot be verified.

[0013] A method for detecting series resistance faults is implemented in a digital electrical power system including a controller that monitors and controls voltages on at least one of the transmission lines, at least one transmitter, and a transmission line in electrical contact with the transmitter, and interacts with at least one receiver in electrical contact with the transmission line. Sample values ​​indicative of line-to-line voltages at the transmitter terminals and the receiver terminals are obtained, with at least one of the voltage sample values ​​being obtained while a current is flowing through at least one of the transmission lines, and the voltage sample values ​​are non-temporarily stored in a computer-readable memory accessible by the controller. Sample values ​​indicative of current in at least one of the transmission lines are obtained along with the voltage sample acquisition within a time window during which the current and voltage at the location on the transmission line at which the sample values ​​are obtained are substantially unchanged, and the current sample values ​​are non-temporarily stored in the computer-readable memory. A difference between the line-to-line voltage at the transmitter and the line-to-line voltage at the receiver is calculated to derive a transmission line series voltage. Each transmission line series voltage is divided by at least one of the stored current sample values ​​to generate a ratio indicative of the transmission line series resistance. These steps are performed at least twice, each iteration being separated by a period, and if the difference in the ratios produced in one or more periods exceeds a predetermined maximum value, the transmitter disconnect device becomes non-conductive, which exceeds the predetermined maximum value indicating a series resistive fault, the resistive fault varying significantly with the current in the transmission line.

[0014] Another method for detecting series resistance faults in a digital electrical power system includes acquiring at least two sample values ​​indicative of line-to-line voltages at receiver terminals, where at least one of the voltage sample values ​​is acquired while current is flowing in at least one of the transmission lines, the acquisition of the voltage sample values ​​being separated by a time period, and the voltage sample values ​​being non-temporarily stored in a computer-readable memory accessible by a controller. Sample values ​​indicative of current in at least one of the transmission lines are acquired, where each current sample value is acquired along with at least one voltage measurement within a time window during which the current and voltage at the location on the transmission line from which the sample value is acquired are substantially unchanged for each set of current sample values ​​and line-to-line voltage sample values. The current sample values ​​are stored in a computer-readable memory accessible by the controller. The stored current sample values ​​are analyzed to identify changes in the current sample values ​​over at least one of the time periods that exceed a predetermined minimum value, and the changes in the current sample values ​​and corresponding changes in the voltage sample values ​​over the same time period are stored. The change in the voltage sample value is divided by the change in the current sample value to calculate a value indicative of the transmission line series resistance, the calculation being valid provided that the line-to-line voltage at the receiver terminals remains substantially constant over at least one period during which the voltage and current sample values ​​are taken. The series resistance value is compared to a predetermined maximum value, and exceeding the predetermined maximum value indicates a series resistance fault. A resistor is placed across the transmission line that is interpreted by the controller as a line-to-line fault, and the controller renders a transmitter disconnect device non-conductive to interrupt power transfer between the transmitter and receiver when the series resistance exceeds the predetermined maximum value.

[0015] Detection of line faults involves periodic measurements of the transmission line voltage (or another sample indicative of the line-to-line voltage at the transmitter and receiver terminals, which may be generally referred to herein as a "voltage sample" or generally as a "voltage measurement"). As will be described in more detail, for long transmission lines, line currents exceeding 2-3 amperes make detection of faults representing excessive power loss in the transmission line more difficult. These faults are referred to as in-line faults. This difficulty can be mitigated by obtaining a signal representing the transmission line voltage, measured at the receiver side of the transmission line. It would be advantageous to be able to verify the receiver-side voltage measurement for accuracy without removing power from the load. The disclosed method can be used to measure and ensure signal integrity, thus preventing false positive or false negative in-line fault determinations.

[0016] As described in Eaves '637, when implementing the PET protocol specific to digital electricity, a portion of the total energy packet period is allocated to transferring energy from the source to the load. This portion is called the transfer period. The remaining time of the packet period is allocated to detecting faults and transferring data. This portion of the packet is called the sample period.

[0017] In a first embodiment of in-line power loss determination, described in Eaves '637, column 4, lines 1-15, a transmitter samples a transmission line voltage taken at the transmitter side of the transmission line during a transmit period when current is allowed to flow through the line. A second measurement is taken by the transmitter during a sample period when no current is flowing. The difference between the two voltage samples represents the voltage drop on the line between the transmitter and receiver. Multiplying the voltage drop by a current measurement made by the transmitter produces a value representing the in-line power loss on the transmission line. If the loss exceeds a predetermined maximum, an in-line power fault is recorded and the transmitter shuts down power to the line to avoid the risk of fire or burns.

[0018] In a second embodiment of in-line power loss determination described in Eaves '637, column 3, lines 50-65, a transmitter takes a measurement of the transmission line voltage at the transmitter terminals during a transmission period and receives, via an external communications link, a second measurement of the transmission line voltage taken by the receiver at the receiver terminals during the transmission period. The difference between the two samples represents the voltage drop on the line between the transmitter and receiver. Multiplying the voltage drop by a current measurement made by the transmitter produces a value representing the in-line power loss on the transmission line.

[0019] In the first embodiment described above, line reflections and electrical noise from external electromagnetic sources and adjacent digital electrical transmission lines make it difficult to accurately measure voltage during the sample period. The difficulty increases as current and power levels increase. Line reflections are more pronounced on transmission lines longer than 2 kilometers. In practice, on these long transmission lines, currents greater than 3 or 4 amps present significant challenges to accurate calculation of in-line power losses, where accuracy within + / - 10 watts is desired. These problems and some solutions are presented in detail in U.S. Patent Application Publication No. 2018 / 0313886 A1 (Mlyniec Line Integrity).

[0020] The second embodiment avoids many of the problems of the first embodiment by using transmitter-side and receiver-side measurements taken during the transfer period and before the transmission line current is interrupted during the sample period. Interruption of the transmission line current is a major cause of line reflections. Furthermore, measurements taken during the transfer period are inherently less susceptible to electrical noise sources because the transmission line impedance is much lower (because the line is not electrically isolated by source and load disconnect devices), which means that much more energy is required to generate noise.

[0021] However, a drawback of the second embodiment that was not anticipated in Eaves '637 is the possibility of improper verification of the receiver voltage measurement. For example, the receiver voltage measurement circuitry may be uncalibrated, or a receiver with a different analog or digital gain factor may be installed incorrectly.

[0022] One less desirable solution to this drawback would be to perform a self-test using a predetermined calibrated test voltage. However, such a test must be performed when the transmission line is not transmitting power, because any current in the line will cause a resistive voltage drop and, therefore, measurement error. Also, performing the test before initial power-up may be impractical, since the line may then be in operation for years without a fresh opportunity for retesting, meaning the test information may quickly become "outdated" and invalid. Because the delivered power is often critical to the operation of customer equipment, it is impractical to periodically de-energize the transmission line to perform the test.

[0023] A second, less desirable solution to this drawback is to perform a test comparing the transmitter voltage with the receiver voltage during the transfer period when current is flowing and use a software / firmware algorithm to filter out the line voltage drop due to current flow. However, this approach may not be practical because the resistance and length of the transmission line must be considered unknown to account for installation errors, and any operator input that defines it may be subject to human error.

[0024] An exemplary advantageous solution presented herein is to perform a calibration test during a sample period rather than during a transfer period, and then use that calibration to verify transmission line voltage measurements made during the transfer period. In other words, the second embodiment proposed by Eaves '637 for measuring transmission line voltage during a transfer period can be combined with a calibration or verification of voltage measurement capability during a sample period.

[0025] When a calibration test is performed during a sample period, the transmitter interrupts current to the transmission line. During the test, both the receiver and transmitter measure the voltage on the transmission line. The receiver communicates the voltage to the transmitter using either the external communication link proposed in Eaves '637 or the in-line communication method disclosed in U.S. Patent No. 9,184,795 (Eaves Communication Patent). The transmitter verifies that the receiver voltage matches its transmitter-side measurement.

[0026] Although the technique seems simple in theory, in practice it can be hampered by line reflections and electromagnetic interference. Line reflections arise from current disturbances when a transmitter disconnect device interrupts the current in the transmission line. Line reflections and interference can appear as "bounced" voltage peaks between the transmitter and receiver.

[0027] This technique utilizes new principles in digital electrical systems to verify receiver voltage measurements.

[0028] During the sample period, when all alternating current (AC) components are reduced, as determined by the transmitter, the voltage at the transmitter terminals and the voltage at the receiver terminals should be equal, even over a distance, despite the fact that at the direct current (DC) level the line voltage may still be attenuated by factors such as line-to-line resistance or even line-to-line interference. If they are not equal, this indicates a hardware fault or miscalibration.

[0029] As described in Eaves '637, both the transmitter and receiver components contain disconnect devices that isolate the transmission line from the energy source and load during the sample period (the disconnect devices are referred to as source disconnect and load disconnect in Eaves '637). Any AC components on the transmission line during the sample period will then be a combination of either line reflections or electrical noise induced on the line. By first identifying when the AC components have decreased to insignificant levels and then isolating them from subsequent voltage samples, which represent only DC attenuation on the transmission line, a valid voltage calibration point can be obtained. If the AC components do not decrease during the sample period, the system is deemed unstable and the transmitter initiates a fault shutdown by opening the disconnect device.

[0030] Safety features in digital electrical systems include a) differential comparison of sequential transmission line voltage measurements, or in the case of in-line faults, b) differential comparison of transmitter terminal voltage measurements made by the transmitter with receiver terminal voltage measurements. Having the ability to verify voltage measurements made by the transmitter and receiver provides a resilient method for ensuring accurate in-line fault measurements.

[0031] A first enhancement to the above method for verifying the integrity of voltage measurements involves measuring the transmission line series resistance (i.e., the cumulative resistance across the electrical current path) at the receiver side of the system. The receiver periodically acquires line-to-line voltage measurements at its input terminals while performing near-simultaneous current measurements (or other sampled measurements indicative of current, which may be referred to herein as "current samples" or generally "current measurements") on at least one of the transmission lines. The voltage and current measurements are stored in the memory of the load controller. The controller analyzes changes in the magnitude of the transmission line current measurements and calculates the corresponding rate of change of the stored voltage measurements. The rate of change of the stored voltage measurements is an indicator of the transmission line resistance (R) and can be calculated as the ratio of the change in voltage (V) to the change in current (I) over two separate instants 1 and 2, as follows:

number

[0032] This evaluation is based on the assumption that the transmitter voltage remained relatively constant during the measurement. A ratio representing the series line resistance is communicated to the transmitter, and the transmitter source controller verifies the assumption that the voltage remained relatively constant during the receiver measurement. The transmitter cuts power to the transmission line if the calculated series resistance exceeds a predetermined maximum value.

[0033] A second enhancement to the method for verifying the integrity of voltage measurements is disclosed for the purpose of detecting in-line resistive faults by detecting current-dependent changes in series resistance due to a higher-than-normal temperature coefficient of resistance (TCR) of the transmission circuit at the concentrated fault contact interface. Arcing or heating from a connection fault, such as a closely spaced broken wire strand or a loose terminal screw, can affect the material properties of the connection interface, such as introducing oxides (due to arcing) or carbon and chlorine from the surrounding polymer insulation. As a result, the relationship between the transmission line's current per unit length and the fault resistance becomes much higher and often nonlinear, compared to typical copper or aluminum conductors, which have a relatively small TCR compared to the fault contact interface.

[0034] Although the in-line fault resistance is much larger than the resistance per unit length of a typical copper or aluminum conductor, the overall resistance can be small compared to the typical series resistance of a long transmission line. However, the time-varying resistance characteristics of in-line faults can be separated from the static resistance of the primarily normal conductor using analog or digital signal processing. [Brief explanation of the drawings]

[0035] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] 1 is an example block diagram of a secure power distribution system. [Figure 2] FIG. 10 is a diagram of a packet energy transmission voltage waveform. [Figure 3] 1 shows in-line power loss determination of a transmission line in the absence of electrical noise or line reflections. [Figure 4] 1 shows in-line power loss determination for long transmission lines with line reflections. DETAILED DESCRIPTION OF THE INVENTION

[0036] Detailed Description The foregoing and other features and advantages of various aspects of the present invention will become apparent from the following more detailed description of various concepts and specific embodiments within the broader scope of the invention. The various aspects of the subject matter introduced above and discussed in more detail below may be implemented in any of numerous ways, as the subject matter is not limited to any particular implementation method. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0037] Unless otherwise defined, used, or characterized herein, terms (including technical and scientific terms) used herein should be construed to have meanings consistent with their accepted meanings in the context of the relevant art, and should not be construed in an idealized or overly formal sense unless expressly so defined herein.

[0038] The terminology used herein is for the purpose of describing particular embodiments and is not intended to limit example embodiments. As used herein, singular forms such as "a" and "an" are intended to include the plural forms as well, unless the context otherwise dictates. Furthermore, the terms "includes," "including," "comprises," and "comprising" specify the presence of stated elements or steps, but do not exclude the presence or addition of one or more other elements or steps.

[0039] A typical digital power system similar to that first described in Eaves '637 is shown in Figure 1. The system includes a voltage source 1 and at least one load 2. The PET protocol is initiated by an operating switch 3, which periodically disconnects the source 1 from the power transmission line 22 electrically coupling the source 1 with the load 2. When switch 3 is in the open (non-conducting) state, the line is also isolated by an isolation diode (D1) 4 from any stored energy that may be present in the load 2.

[0040] Eaves' 637 suggests several versions of an alternative switch that can replace isolation diode 4, and all versions can produce similar results when used in the manner presently described. Capacitor C35 represents the energy storage element on the load side of the circuit.

[0041] Transmission line 22 has an inherent line-to-line resistance R46 and capacitance C17. As described in Eaves '637, the PET system architecture adds line-to-line resistance R38 and capacitance C29. At the instant switch 3 is opened, capacitances C17 and C29 store a charge that decays at a rate inversely proportional to the sum of resistances R46 and R38. Capacitor C35 does not discharge through resistors R38 and R46 due to the reverse blocking action of isolation diode D14. The amount of charge contained in capacitors C17 and C29 is proportional to the voltage across them and can be measured at points 16 and 17 by source controller 18 or load controller 19.

[0042] As explained in Eaves '637, changes in the decay rate of the energy stored in capacitances C17 and C29 can indicate the presence of a line-to-line fault on transmission line 22. As presented in Eaves '637, the difference between normal operation 27 and a fault 28 is shown in FIG.

[0043] 1, the combination of switch S13, source controller 18, resistor R110, switch S211, resistor R212, switch S313, and resistor R38 may be referred to as transmitter 20. The combination of switch S415, resistor R514, switch S534, resistor R633, load controller 19, diode D14, capacitor C29, and capacitor C35 may be referred to as receiver 21.

[0044] As specified in Eaves '637, a method for measuring in-line resistance without a communication link is shown in Figure 3, which illustrates the ideal case with no line reflections or external electrical noise. Transmitter 20 measures its terminal voltage and current nearly simultaneously during the same energy transfer period, in a first sample 23, just before opening source disconnect switch S13. Transmitter 20 then opens disconnect switch S13 and immediately acquires another voltage sample 25. The difference between first voltage sample 23 and second voltage sample 25 is proportional to the line resistance. The voltage difference between first voltage sample 23 and second voltage sample 25 is independent of the normal gradual voltage decay that occurs during the remainder of the sample period, because second voltage sample 25 is acquired before the voltage on transmission line 22 has had time to decay significantly. Multiplying the voltage difference by the current measurement yields the value of in-line power loss.

[0045] FIG. 4 shows the transmission line voltages seen at transmitter 20 (solid line) and receiver 21 (dashed line) for longer transmission lines and / or higher currents. In this case, line reflections add complexity to the simple in-line power loss calculation described in FIG. 3. At point 29, when transmitter disconnect switch S13 is opened, the line voltage at transmitter terminal 24 is higher than the line voltage at receiver terminal 26 due to the voltage drop as current passes through the resistance of transmission line 22. As can be seen from the difference in the horizontal positions of points 29 and 30 in FIG. 3 (representing the voltages at transmitter terminal 24 and receiver terminal 26, respectively), there is also a time delay between when disconnecting the transmitter causes voltage drop 29 first seen at transmitter terminal 24 and when drop 30 is first seen at receiver terminal 26, due to inductive and capacitive elements in line 22. Using numerical processing techniques well known in the signal processing industry, the transmit and receive processors can determine, at point 31, when the AC component of the transmission line voltage has decreased to an insignificant value and when the remaining voltage change is DC attenuation due to line-to-line resistance or line-to-line faults on transmission line 22, both of which are forms of DC attenuation. Further improvements for separating DC attenuation from AC components are described in the Mlyniec Line Integrity Patent, although Mlyniec did not disclose the ability to verify receiver side measurements. At point 32, the transmitter again closes disconnect switch S13 and the voltage on transmission line 22 rises.

[0046] It is within the region between points 31 and 32 that the voltage measured at transmitter terminal 24 and the voltage measured by receiver terminal 26 coincide. Both transmitter 20 and receiver 21 then calculate the average voltage value for the period between points 31 and 32. Receiver 21 transmits the measured average voltage value to transmitter 20 using the communications link described in Eaves '637 or using a communications data stream provided on transmission line 22 as described in the Eaves Communication Patent.

[0047] In some cases, it may be useful for the transmitter 20 to vary the value of its voltage source to perform voltage measurements over a wider range and therefore test whether the voltage measurements by the receiver 21 and the transmitter 20 continue to match during the DC decay period. This technique can reveal problems related to gain errors in the analog or digital calibration of voltage-sensing components. Alternatively, this technique can be used to verify whether the transmitter 20 is communicating with the correct receiver 21 by varying the power supply voltage according to a predetermined pattern, especially when an external communication link is used, as communication connections may be accidentally made between the wrong transmitter 20 and receiver 21 pair.

[0048] A first enhancement to the above method for verifying the integrity of voltage measurements involves measuring the transmission line in-line (series) resistance at the receiver side of the system. Referring to FIG. 1, the receiver 21 periodically acquires line-to-line voltage measurements at its input terminals while performing near-simultaneous transmission line current measurements. The voltage and current measurements are stored in the computer-readable memory of the receiver load controller 19. The load controller analyzes changes in the magnitude of the transmission line current measurements and calculates the corresponding rate of change (represented by Equation 1 above) of the stored voltage measurements. The ratio indicates the transmission line series resistance (i.e., the cumulative resistance across the current path through the transmission line), assuming that the voltage remains relatively constant during the measurement time. The ratio representing the transmission line series resistance is communicated to the transmitter 20, whose transmitter source controller 18 verifies the assumption that the voltage remains relatively constant during the receiver measurement. The transmitter disconnects power to the transmission line by opening S1 Source Disconnect 3 if the calculated transmission line series resistance exceeds a predetermined maximum value.

[0049] One modification to the above method for measuring transmission line series resistance at the receiver is for the receiver load controller 19 to operate the S5 switch 34 to allow an internal load 33 (e.g., in the form of a resistor or other circuit capable of changing current levels) to apply a load current to the transmission line 22, as shown in FIG. 1 . Alternatively, the receiver load controller 19 can operate the S4 switch 15 to allow the internal load 14 to apply a load current to the transmission line during a transfer period when the transmitter disconnect device is in a conductive state, during which the application of the load is not interpreted by the transmitter as a line-to-line fault. This implementation provides a direct method of affecting changes in transmission line current that is independent of changes in current demand from the external load 2. As described in U.S. Pat. No. 9,419,436, the external load 2 can be connected or disconnected by operation of the receiver load controller 19 while the internal load 33 is applied. If the external load 2 is not disconnected when the internal load 33 is applied, the load controller 19 can perform calculations to ensure that the receiver 21 has sufficient capacity to handle both loads simultaneously before activating the internal load 33.

[0050] If the external load 2 is disconnected, the receiver 21 performs a self-check function during startup or restart. If the external load 2 is not disconnected while the internal load 33 is applied, the internal load 33 is added to the normal external load 2 on the receiver 21, thereby preventing the operation of the external load 2 from being disabled. If a resistor is used as the internal load 33, the current on the transmission line 22 due to the internal load 33 is a fixed resistance and therefore a known value. For example, the load current can be calculated by the load controller 19 by dividing the receiver terminal voltage by the known load resistance. In another variation, the internal load 33 can be replaced by a DC-DC converter circuit that provides a controllable internal load current. In a further variation, a current sensor can be applied to the internal load circuit to provide a direct measurement of the current to the load controller 19.

[0051] In yet another modification, rather than communicating a value indicative of the series transmission line resistance to the transmitter for fault determination, the receiver load controller 19 can initiate a transmitter shutdown by closing the S4 switch 15 at the receiver. Closing the S4 switch 15 connects the R5 pull-down resistor 14 between the conductors of the transmission line 22. If the pull-down is activated for a sufficient period of time, it is resolved by the transmitter 20 as a line-to-line fault, as described in prior art Eaves '637. To further verify the fault determination, the receiver 21 can communicate with the transmitter 20 to verify the transmitter output voltage that was present while the receiver voltage measurements were taken, or in a simplified embodiment, the receiver 21 can simply assume that the transmitter voltage was held constant during the receiver measurements.

[0052] A second enhancement to the method for verifying the integrity of voltage measurements is disclosed for the purpose of detecting in-line (series) resistance faults by detecting current-dependent changes in series resistance due to the transmission circuit's higher-than-normal temperature coefficient of resistance (TCR) at the contact interface of a concentrated fault. The TCR method detects dynamic changes in transmission line series resistance resulting from the much larger and often nonlinear TCR due to in-line faults. Arcing or heating from a connection fault, such as a loose joint or terminal screw, can affect the material properties of the connection interface by introducing foreign particles such as oxides, carbon, and chlorine, some of which are introduced from the surrounding polymer insulation. The resistance of the fault can be small compared to the normal series resistance of a long transmission line 22. However, the time-varying resistance characteristics of an in-line fault can be separated from the static resistance of the primarily healthy conductor using analog or digital signal processing.

[0053] The TCR method can enhance the in-line resistance calculation method taught by Eaves '637 and can also enhance the method described herein, in which transmitter and receiver acquired voltages are compared for validation. In the TCR method, samples representing voltages at the transmitter and receiver terminals are taken, closely spaced in time, with at least one of the voltage measurements being made while current is flowing through the transmission line 22. At least one sample of the transmission line current is made substantially simultaneously with the voltage sample, with the characterization of "substantially the same time" including a short time difference during which the current and voltage do not change significantly (e.g., 1%, 2%, 3%, or less) at the measurement location. The difference between the voltage samples is divided by the current to generate a value indicative of the series resistance of the transmission line circuit. The voltage and current samples and resistance calculation are performed again after a predetermined period of time. Under normal conditions without in-line resistive faults, the resistance value over that period should remain relatively constant even as the line current changes.

[0054] When a series fault is present, the larger and often nonlinear TCR of the fault contact interface introduces excessive changes in line resistance during the sample period. This fault contact area includes the affected material at and around the fault contact interface, which is typically the cable insulation, cable filler, and other components of the cable, but may also include other external materials affected by the temperature increase, especially if the cable insulation is compromised. Depending on the material composition of the fault contact area, the TCR can become a large negative value, meaning that resistance decreases over time for a given current as ohmic heating increases the temperature of the contact area. Because power applied to the fault contact area is proportional to the square of the transmission line current, a strong nonlinear relationship is established between the transmission line series resistance and current. This nonlinear relationship may be further reinforced by the TCR itself, which changes with temperature due to the complex material properties of the fault contact area compared to the TCR of a normal transmission line conductor. Due to these non-linear relationships, it may be advantageous to extend the time that the circuit is disabled after a fault is detected and before restarting to allow the contact area to cool, thus providing a significantly higher and more easily detectable initial resistance for positive TCR materials, or a significantly lower initial resistance for negative TCR materials.

[0055] As described herein, the transmitter initiates the shutdown of power to the transmission line by placing S1 Transmitter Disconnect 3 in a non-conducting (open) state. An alternative method for stopping power to transmission line 22 is to control the transmitter power conversion circuitry to provide near-zero voltage and / or current, or values ​​safe for human contact and fire protection. Methods for achieving this result are disclosed in claims 8 and 12 of Eaves '637. It is well known in the industry that many power converters provide control inputs that allow the voltage and / or current to be reduced to low values ​​during a fault condition.

[0056] For all methods that obtain multiple sample values ​​within a time window when the current and voltage on the transmission line are substantially unchanged (i.e., near-simultaneous sampling measurements), the tolerance for the timing of the samples is determined by the system design. Because the load's current draw may change over time and other external factors may apply, delays between samples within the sampling period introduce increased error. Circuit elements such as capacitor C35 can reduce the rate at which load changes affect the circuitry at the transmitter output terminal 16 and the receiver input terminal 17, increasing the delay between samples within the sampling period. Therefore, the maximum time allowed to complete one set of near-simultaneous sampling measurements is defined by how much measurement error is acceptable based on selected limits and how much change in the load's current draw can affect the circuitry at the transmitter output terminal 16 and the receiver input terminal 17 within that period.

[0057] There are several numerical techniques known in the signal processing industry for extracting the average voltage value between points 28 and 30 in Figure 3. These techniques may include simple averaging, digital filtering, or interpolation, some of which are described in the Mlyniec Line Integrity Patent. Alternatively, the signal processing task performed by receiver 21 may be offloaded to transmitter 20 by transmitting "raw" voltage measurements from receiver 21 to transmitter 20.

[0058] The systems and methods of the present disclosure can be implemented in a computing system environment. Examples of well-known computing system environments and their components that may be suitable for use with the systems and methods include, but are not limited to, personal computers, server computers, handheld or laptop devices, tablet devices, smartphones, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics devices, networked personal computers (PCs), minicomputers, mainframe computers, and distributed computing environments that include any of the above systems or devices. Common computing system environments and their operation and components are described in many existing patents (e.g., U.S. Patent No. 7,191,467, owned by Microsoft Corp.).

[0059] The methods may be implemented through non-transitory computer-executable instructions, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular types of data. The methods may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media, including memory storage devices.

[0060] The processes and functions described herein may be non-transitory stored in a computer in the form of software instructions. Components of a computer may include, but are not limited to, a computer processor, a computer storage medium serving as memory, and a system bus coupling various system components including the memory to the computer processor. The system bus may be any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures.

[0061] A computer typically includes one or more of a variety of computer-readable media that can be accessed by a processor and that can include both volatile and nonvolatile media, and removable and non-removable media. By way of example, computer-readable media can include computer storage media and communication media.

[0062] Computer storage media can store software and data in a non-transitory state and include both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of software and data such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed and executed by a processor.

[0063] Memory includes computer storage media in the form of volatile and / or nonvolatile memory such as read-only memory (ROM) and random access memory (RAM). The basic input / output system (BIOS), containing the basic routines that transfer information between elements within the computer, such as during start-up, is typically stored in ROM. RAM typically contains data and / or program modules that are immediately accessible to and / or presently being operated on by the processor.

[0064] A computer may also include other removable / non-removable, volatile / non-volatile computer storage media, such as (a) hard disk drives that read from or write to non-removable, non-volatile magnetic media, (b) magnetic disk drives that read from or write to removable, non-volatile magnetic disks, and (c) optical disk drives that read from or write to removable, non-volatile optical disks, such as CD-ROMs or other optical media. The computer storage media may be coupled to the system bus by a communications interface, which may include, for example, conductive wire and / or fiber optic paths for transmitting digital or optical signals between components. Other removable / non-removable, volatile / non-volatile computer storage media that may be used in the exemplary operating environment include magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid-state RAM, solid-state ROM, and the like.

[0065] The drives and their associated computer storage media provide storage of computer-readable instructions, data structures, program modules, and other data for the computer. For example, a computer's internal or external hard disk drive may store an operating system, application programs, and program data.

[0066] Accordingly, the scope of the disclosed invention should be determined by the appended claims and their legal equivalents, rather than by the examples shown. In describing embodiments of the invention, specific terminology is used for the sake of clarity. For purposes of description, specific terminology is intended to include, at a minimum, technical and functional equivalents that operate in a similar manner to achieve a similar result. Furthermore, in some instances where a particular embodiment of the invention includes multiple system elements or method steps, those elements or steps may be replaced with a single element or step, and similarly, a single element or step may be replaced with multiple elements or steps that serve the same purpose. Furthermore, while the invention has been shown and described with reference to specific embodiments thereof, those skilled in the art will recognize that various substitutions and changes in form and detail may be made therein without departing from the scope of the invention. Furthermore, other aspects, features, and advantages are within the scope of the invention, and all embodiments of the invention need not necessarily achieve all advantages or possess all of the characteristics described above. Furthermore, steps, elements, and features discussed herein in connection with one embodiment may be used in connection with other embodiments as well. Furthermore, components, steps, and features identified in the Background section are essential to this disclosure and can be used in conjunction with, or substituted for, components and steps described elsewhere in this disclosure within the scope of the present invention. In method claims, when steps are described in a particular order (with or without an ordered prefix for ease of reference), the steps should not be construed as being limited in time to the order in which they are described unless otherwise specified or implied by the terms and phrases.

Claims

1. 1. A method for detecting series resistance faults, comprising: a) in a digital electrical power system comprising at least one transmitter and a transmission line in electrical contact with said transmitter, using a controller to monitor and control voltage on at least one of said transmission lines and to interact with at least one receiver in electrical contact with said transmission line; b) obtaining sample values ​​indicative of line-to-line voltages at the transmitter terminals and the receiver terminals, at least one of the voltage sample values ​​being obtained while current is flowing through at least one of the transmission lines, and non-temporarily storing the voltage sample value in a computer-readable memory accessible by the controller; c) acquiring sample values ​​indicative of current in at least one of the transmission lines in conjunction with the acquisition of the voltage samples within a time window during which the current and voltage at the locations on the transmission lines at which the sample values ​​are acquired are substantially unchanged, and non-temporarily storing the current sample values ​​in the computer-readable memory; d) calculating the difference between the line-to-line voltage at the transmitter and the line-to-line voltage at the receiver to derive a transmission line series voltage; e) dividing the transmission line series voltage by at least one of the stored current sample values ​​to generate a ratio indicative of the transmission line series resistance; f) performing steps (b) through (e) at least twice, each iteration separated by a time period, and rendering the transmitter disconnect device non-conductive if the difference in the ratios produced in one or more time periods exceeds a predetermined maximum value, the exceeding of the predetermined maximum value indicating a series resistive fault, the resistive fault varying significantly with transmission line current; and A method comprising:

2. 2. The method of claim 1, wherein the transmitter disconnect is placed in the non-conductive state after fault detection and prevented from restarting for a time sufficient to allow a series fault contact area to cool before being placed back in a conductive state to verify the fault, and a larger detectable series resistance change can be detected when current is reapplied to the transmission line due to the non-linear relationship between series resistance and current at the series fault contact area.

3. The method of claim 1 , wherein steps (b) through (e) are performed at the transmitter or the receiver.

4. 1. A method for detecting series resistance faults, comprising: a) in a digital electrical power system, comprising: (i) at least one transmitter including a transmit terminal; and (ii) a transmission line in electrical contact with said transmitter terminal, using a controller to monitor and control voltage on at least one of said transmission lines and to interact with at least one receiver including a receiver terminal in electrical contact with said transmission line; b) obtaining at least two sample values ​​indicative of line-to-line voltages at the receiver terminals, wherein at least one of the voltage sample values ​​is obtained while current is flowing through at least one of the transmission lines, the obtaining of the voltage sample values ​​being separated by a time period, and non-temporarily storing the voltage sample values ​​in a computer-readable memory accessible by the controller; c) obtaining sample values ​​indicative of current in at least one of the transmission lines, each current sample value being obtained along with at least one of the voltage measurements within a time window during which the current and voltage at the location on the transmission line at which the sample value is obtained are substantially unchanged for each set of current sample values ​​and line-to-line voltage sample values, and non-temporarily storing the current sample values ​​in a computer-readable memory accessible by the controller; d) analyzing the stored current sample values ​​to identify a change in the current sample value over at least one of the time periods that exceeds a predetermined minimum value, and storing the change in the current sample value and the corresponding change in the voltage sample value over the same time period; e) dividing the change in the voltage sample values ​​by the change in the current sample values ​​to calculate a value indicative of transmission line series resistance, said calculation being valid provided that the line-to-line voltage at the transmitter terminals remains substantially constant over the at least one period over which the voltage sample values ​​and the current sample values ​​are taken; f) comparing the series resistance value with a predetermined maximum value, exceeding the predetermined maximum value indicating a series resistance fault and operative to place a resistor across the transmission line which is interpreted by the controller as a line-to-line fault, the controller placing a transmitter disconnect device in a non-conductive state to interrupt power transfer between the transmitter and the receiver when the series resistance exceeds the predetermined maximum value; A method comprising:

5. 5. The method of claim 4, wherein the controller is within the transmitter, the method further comprising transmitting the voltage sample values ​​and the current sample values ​​to the controller, the controller performing the calculations to provide the value indicative of the transmission line series resistance, and the controller verifying that the transmitter had an output voltage that remained substantially constant during the period that the voltage sample values ​​and the current sample values ​​were taken before disconnecting the transmitter to the non-conductive state if the value indicative of the transmission line series resistance exceeds the predetermined maximum value.

6. 5. The method of claim 4, wherein the controller is within the transmitter, the method further comprising communicating an output voltage of the transmitter to the receiver, and wherein a second controller within the receiver verifies that the transmitter output voltage remains substantially unchanged while the voltage and current samples are being taken.

7. 5. The method of claim 4, wherein the second controller within the receiver has a predetermined resistance value to activate a load internal to the receiver and to drive a current through the transmission line, and wherein a value indicative of the transmission line series resistance is calculated using a current in the transmission line independent of a load at the receiver output.

8. 8. The method of claim 7, wherein the internal load is applied only if the receiver has sufficient capacity to handle the external load and the internal load simultaneously.

9. The method of claim 4 , wherein steps (b) through (f) are performed in the receiver.

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