Method for mitigating circulating currents and voltages of different minor sections of cross-bonded cables

Abstract

Disclosed herein, a novel end-bonding method for mitigating excessive circulating currents and voltages within the metallic sheath of existing cross-bonded (CB) power cables The circulation of currents and voltages arises due to unbalanced minor section lengths caused by cable route modifications. The end-bonding method of the present invention addresses this issue in existing CB cable infrastructure without altering the original cable sections. It comprising identifying a last set of cable joints typically marking the end of minor section, associating link box containing these last set of joints where the outer protective sheaths of all the joints are connected together to form common grounding point, and connecting the common grounding point to special voltage limiting device (SVL). This configuration reduces current flow in the joints and controls sheath voltage within safe range, thereby enhancing the reliability and lifespan of such cable systems.

Description

METHOD FOR MITIGATING CIRCULATING CURRENTS AND VOLTAGES OF DIFFERENT MINOR SECTIONS OF CROSS-BONDED CABLESFIELD OF THE INVENTION:

[0001] The present invention relates generally to the field of high voltage electrical cable systems and more particularly relates to a method for mitigating circulating currents and voltages in the sheath of existing cross-bonded cables of different minor section length.BACKGROUND:

[0002] In the realm of high-voltage power transmission and distribution, single core shielded HVAC (High-Voltage Alternating Current) power cables reign supreme. These workhorse cables rely on a crucial component, a metallic sheath, to perform a trio of essential functions.

[0003] Firstly, the metallic sheath acts as an electrical shield, safeguarding the individual phase conductors within the cable from the disruptive effects of electromagnetic interference. A complex network of power lines, all carrying high voltage electricity. These lines can generate electromagnetic fields that can interfere with the proper functioning of the cables themselves. The metallic sheath acts as a shield, absorbing these stray fields and preventing them from reaching the delicate inner conductors.

[0004] Secondly, the metallic sheath plays a vital role in waterproofing the cable. Moisture ingress, or the entry of water, can be detrimental to the cable's insulation. The sheath acts as a barrier, preventing water from contacting the insulation and compromising its integrity. This ensures the cable continues to function reliably and safely.

[0005] Finally, the metallic sheath provides much-needed mechanical support to the cable. High-voltage power cables can be quite hefty, and the metallic sheath adds crucial structuralrigidity. This rigidity helps the cable maintain its shape and withstand the stresses encountered during installation, operation, and potential environmental challenges. However, due to inductive and capacitive effects, the metallic sheath will always carry a circulating current and have a voltage relative to ground.

[0006] IEEE Standard 575 addresses the need to minimize these sheath currents and voltages. Excessive current can lead to ohmic losses, while high voltage can limit the cable's ampacity (current carrying capacity). The standard recommends the use of a technique known as "cross bonding" (CB) to achieve this goal.

[0007] In a CB system, the entire cable network is divided into major sections, with each major section solidly grounded to earth through a grounding resistor at one end. Within a major section, the metallic sheath of each phase is connected (bonded) to another phase in a link box via a sheath voltage limiter (SVL). This configuration creates three "minor sections" within each major section.

[0008] To maintain minimal current and voltage in the sheath, the length of each minor section must be balanced within 10% of the others as specified in IEEE Standard 575.

[0009] However, practical challenges can arise when modifying existing cable routes. A utility sector in Maharashtra, India, reported a scenario where a cable route needed to be changed, requiring the replacement of an existing minor section with a new one of different length as shown in Fig. 1.

[0010] According to the standard, a significant imbalance in minor section lengths can lead to high circulating currents and voltages across the cable sheath joints and terminals. Since statistics show that most ground faults in CB HV cables occur at joints and terminals, it is crucial to minimize voltage and current at these points.

[0011] Hence, there is a need for a new end-bonding method that can mitigate high current and voltage across joints and terminals in existing CB systems, even when a minor section length is changed.

[0012] The present invention proposes a method that is applicable without modifying the existing two sections of the cable route.OBJECTIVES OF THE INVENTION:

[0013] The primary objective of the present invention is to develop a new end bonding technique to reduce circulating current and voltage in the sheath cross-bonded cable.

[0014] Another objective of the present invention is to handle the circulating current and voltage across different joints in a non-uniform length of the minor section in a cross-bonded cableSUMMARY:

[0015] The present invention relates to a novel end-bonding method for existing crossbonded (CB) power cables. This method specifically addresses the challenge of excessive circulating currents and voltages arising within the metallic sheath of these cables due to unbalanced minor section lengths. Such imbalances often occur when modifications are made to existing cable routes.According to the present invention, the method comprising:• identifying the last set of cable joints, where these Straight-through (ST) joints typically mark the end of a minor section;• associating the link box within these last set of cable joints wherein the sheath terminals of all the joints are connected together to form a common terminal point; and• connecting the common terminal formed by the connection of the sheath terminals of the last set of cable joints to a special voltage limiting device (SVL).

[0016] The selection of the SVL is based on its impedance characteristics to ensure effective voltage limitation under steady-state operating conditions.

[0017] Further, The SVL acts as a high impedance path in the circuit. Under steady-state operating conditions, the SVL behaves like an open circuit, limiting the voltage across different parts of the cable sheath within a safe range (typically less than 50 volts as recommended by relevant standards).

[0018] Further, the end-bonding method is implemented on existing CB cable systems without altering the original cable sections, making it a practical solution for addressing the problem in existing infrastructure. By connecting the sheath terminals together, current circulation within the individual joints is minimized, effectively reducing the overall current flow through the sheath.

[0019] These objectives and advantages of the present invention will become more evident from the following detailed description when taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS:The objective of the present invention will now be described in more detail with reference to the accompanying drawing, wherein:Fig. 1 shows schematic diagram of a major section in a CB cable with a new minor cable route for a third minor section;FIG. 2 shows schematic diagram of a major section in a CB cable with solid grounding at the end;Fig. 3 shows an equivalent circuit for inductive effect in CB cable with solid grounding at the end;Fig. 4 shows equivalent circuit for capacitive effect in CB cable with solid grounding at the end;Fig. 5 shows schematic diagram of a major section in CB cable grounded with SVL at the end;Fig. 6 shows schematic diagram of a major section in CB cable with three straight-through joints connected together at the end with SVL;Fig. 7 shows equivalent circuit for inductive effect in CB cable with three straight-through joints connected together at the end with SVL;Fig. 8 shows equivalent circuit for capacitive effect in CB cable with three straight- through joints connected together at the end with SVL;Fig. 9 shows the experimental setup to measure current and voltage at different joints for the proposed end bonding method;Fig. 10 shows measured (a) ST joints and (b) CB joints current of 3m long third minor section for solid grounding;Fig. 11 shows measured (a) ST joints and (b) CB joints voltage of 3m long third minor section for solid grounding;Fig. 12 shows measured (a) ST joints and (b) CB joints current of 7m long third minor section for solid grounding;Fig. 13 shows measured (a) ST joints and (b) CB joints voltage of 7m long third minor section for solid grounding;Fig. 14 shows measured (a) ST joints and (b) CB joints current of 3m long third minor section for sheath grounded with SVL;Fig. 15 shows measured (a) ST joints and (b) CB joints voltage of 3m long third minor section for sheath grounded with SVL;Fig. 16 shows measured (a) ST joints and (b) CB joints current of 7m long third minor section for sheath grounded with SVL;Fig. 17 shows measured (a) ST joints and (b) CB joints voltage of 7m long third minor section for sheath grounded with SVL;Fig. 18 shows measured (a) ST joints and (b) CB joints current of 3m long third minor section for the proposed method;Fig. 19 shows measured (a) ST joints and (b) CB joints voltage of 3m long third minor section for the proposed method;Fig. 20 shows measured (a) ST joints and (b) CB joints current of 7m long third minor section for the proposed method;Fig. 21 shows measured (a) ST joints and (b) CB joints voltage of 7m long third minor section for the proposed method;Fig. 22 shows measured (a) ST joints and (b) CB joints current for the proposed method case II and original case study;Fig. 23 shows measured (a) ST joints and (b) CB joints voltage for the proposed method case II and original case study;Fig. 24 shows simulated (a) ST joints and (b) CB joints current of 150m long third minor section for solid grounding;Fig. 25 shows simulated (a) ST joints and (b) CB joints voltage of 150m long third minor section for solid grounding;Fig. 26 shows simulated (a) ST joints and (b) CB joints current of 300m long third minor section for solid grounding;Fig. 27 shows simulated (a) ST joints and (b) CB joints voltage of 300m long third minor section for solid grounding;Fig. 28 shows simulated (a) ST joints and (b) CB joints current of 650m long third minor section for solid grounding;Fig. 29 shows simulated (a) ST joints and (b) CB joints voltage of 650m long third minor section for solid grounding;Fig. 30 shows simulated (a) ST joints and (b) CB joints current of 800m long third minor section for solid grounding;Fig. 31 shows simulated (a) ST joints and (b) CB joints voltage of 800m long third minor section for solid grounding;Fig. 32 shows simulated (a) ST joints and (b) CB joints current of 150m long third minor section for sheath grounded with SVL;Fig. 33 shows simulated (a) ST joints and (b) CB joints voltage of 150m long third minor section for sheath grounded with SVL;Fig. 34 shows simulated (a) ST joints and (b) CB joints current of 300m long third minor section for sheath grounded with SVL;Fig. 35 shows simulated (a) ST joints and (b) CB joints voltage of 300m long third minor section for sheath grounded with SVL;Fig. 36 shows simulated (a) ST joints and (b) CB joints current of 650m long third minor section for sheath grounded with SVL;Fig. 37 shows simulated (a) ST joints and (b) CB joints voltage of 650m long third minor section for sheath grounded with SVL;Fig. 38 shows simulated (a) ST joints and (b) CB joints current of 800m long third minor section for sheath grounded with SVL;Fig. 39 shows simulated (a) ST joints and (b) CB joints voltage of 800m long third minor section for sheath grounded with SVL;Fig. 40 shows simulated (a) ST joints and (b) CB joints current of 150m long third minor section for the proposed method;Fig. 41 shows simulated (a) ST joints and (b) CB joints voltage of 150m long third minor section for the proposed method;Fig. 42 shows simulated (a) ST joints and (b) CB joints current of 300m long third minor section for the proposed method;Fig. 43 shows simulated (a) ST joints and (b) CB joints voltage of 300m long third minor section for the proposed method;Fig. 44 shows simulated (a) ST joints and (b) CB joints current of 650m long third minor section for the proposed method;Fig. 45 shows simulated (a) ST joints and (b) CB joints voltage of 650m long third minor section for the proposed method;Fig. 46 shows simulated (a) ST joints and (b) CB joints current of 800m long third minor section for the proposed method;Fig. 47 shows simulated (a) ST joints and (b) CB joints voltage of 800m long third minor section for the proposed method;Fig. 48 shows simulated maximum RMS current for (a) first set of ST joints (b) second set of ST joints (c) first set of CB joints (d) second set of CB joints of different third minor section lengths for different bonding methods;Fig. 49 shows simulated maximum RMS Voltage for (a) first set of ST joints (b) second set of ST joints (c) first set of CB joints (d) second set of CB joints of different third minor section lengths for different bonding methods;Fig. 50 shows simulated (a) ST joints and (b) CB joints current for the proposed method case I and original case study;Fig. 51 Shows simulated (a) ST joints and (b) CB joints voltage for the proposed method case I and original case study; andFig. 52 shows transient conditions of (a) Simulated peak current (b) Simulated peak voltage across all joints in the first phase.REFERENCE NUMERALS10 - 3 -Phase Load11 - 3-Phase Voltage Source12 - MultimeterDETAILED DESCRIPTION OF THE INVENTION:

[0020] The present invention disclosed herein addresses a critical challenge encountered in existing cross-bonded cable systems with unbalanced minor section lengths. The invention proposes a novel end-bonding method specifically designed to mitigate excessive circulating currents and voltages within the metallic sheath of these cables.

[0021] In accordance to the present invention, it is required to change the cable route, in doing so, sometimes the reaming part of the cable length is not the same compared to the existing two sections. This imbalance in length causes a huge circulating current and voltage throughout the sheath. As per the investigation and experimental find out that this problem is handled with a special type of end bonding method. This includes connecting the sheath terminals of the last set of ST joints together and then connecting them with an SVL. By using the method of the present invention, the current in the joints is minimal and also the voltage across different across different parts of the cable is within 50V (standard range).

[0022] In the following section of the description, the detailed theory about the circuit model of the bonding method disclosed in the present invention and the other existing technique is discussed herein in the section I. As further in the II and III subsections, the formulae of current and voltage in the joints for different types of is end bonding technique is presented. In the final subsection, the details about the practical and simulated results were presented.I) Circuit model of different types of end bonding of sheathThe circulating current and standing voltage in the sheath of the joints is mainly due to the inductive and capacitive effect between the cable conductor and the sheath. The inductive effect is due to the magnetic flux produced by the current-carrying conductor linking the metallic sheath and producing a pseudo voltage due to Maxwell's laws of electromagnetism, therefore is represented by the current control voltage source. The capacitive effect is due to the phase voltage in each minor section. The analytical relation between the per-phase voltage (7) and per-unit capacitive current (7C) in the metallic sheath is Ic= jc CV. The capacitive current flows out from the middle of each section

[0012] , and since the capacitive current is dependent on per-phase voltage, it is represented by the voltage control current source.To estimate the current and voltage in the joints sheath, the accurate analytical description of the per unit impedance (Zs) of the sheath is required and for a trefoil cable laid formation it is given as:In equation (1), Rsis the resistance of the sheath, Lsis the self-inductance of the sheath caused by the circulating current, Mcsand Mssare the mutual inductance between the current- carrying conductor in each phase to the measuring sheath and the mutual inductance between other phase sheaths to the measuring sheath.The analytical formula to obtain each of the above-mentioned terms for a trefoil formation of the cable obtained as:In the above formulae kr, kt, and T are the metal sheath resistivity, temperature, and ambient temperature respectively. rosand risare the inner and outer radius of the metallic sheath, and rcsand rssare the average distance between the conductor of one phase to the sheath of the calculating phase and the sheath of one phase to the sheath of the calculating phase respectively. In this paper, it is considered that the impedance of the cable for all the phases in each minor section are same i.e. impedance of the cable for the first minor section and all the phases are considered as Zsa, similarly Zsb, and Zsnfor the second and third minor section which is obtained analytically using equation (1). Therefore, total sheath impedance of a particular phase of a major section in the cable are represented as:From the above-mentioned analytically obtained electrical parameters, the induced voltage per unit length and capacitive effect current is obtained as:(6)In equation (6), Vi is the voltage of the particular phase, and is the per unit length capacitance between the conductor and the metallic sheath and analytically obtained as:In equation (7), is the relative permittivity of the insulating material, and rcis the conductorradius. Throughout the paper, i=l, 2, and 3 for three different phases.To mitigate the excessive circulating current and standing voltage (due to inductive and capacitive effect) in the sheath caused due to irregular in the length of the third minor section, three end bonding methods at the last set of straight-through joints are described below:A. Last Set of Straight joints are individually solidly groundedThe Fig. 2. Represents the schematic diagram of a major section in CB cable with solid grounding at the end. This is the simplest method to mitigate the circulating current for non-uniform thirdminor section length CB cable is to solidly ground the terminals of the last set of ST joints (ST4, ST5, and ST6) with a low value of grounding resistance. (RG4, RG, and RG6) individually as shown in Fig. 2. The value of the grounding resistance for the HV cable system is generally kept below 0.2Q. The circuit diagram for inductive and capacitive effects is shown in Fig .3 and Fig. 4 respectively.B. Last Straight joints are individually grounded with SVLThe high circulating current and standing voltage for a non-uniform third minor section length can also be mitigated, by individually grounding the terminals of the last set of ST (ST4, ST5, and ST6) with an SVL (ZSVL) as shown in Fig. 5. Thus, the end of the sheath is open during steady state condition and solidly grounded during transients. The circuit diagram for inductive and capacitive effects is the same as solidly grounded, except in the place of RG4, RG5, and RG6is ZSVL.C. Last Straight through joints are connected and grounded together with SVLTo eliminate the excessive sheath current and standing voltage in the joints of a CB cable for a nonuniform length third minor section, the proposed method is to merge the above two methods (connecting other phases to cancel out inductive effect from solidly grounded and introduction of SVL from grounding with SVL) by connecting the three terminals of ST4, ST5, and ST6 together in the link box and then connect the terminal with an SVL as shown in Fig. 6. Under steady state condition the SVL act as an open circuit and solidly grounded during transients. The inductive and capacitive model of the proposed method is shown in Fig. 7 and 8.To compare the best last terminal end bonding method of the above-discussed, the circulating current and the standing voltage across the joints are obtained analytically in the section below.II) Mathematical modelling of total current in the joints for different types of end bondingWhile performing the analytical operations, it is considered that during steady state conditions Zsvt» ZST, and the impedance of the grounding resistance « total impedance of the cable sheath and Zsvt. The current and voltage in the joints for solidly grounded, grounded with SVL, and the proposed method type of bonding is presented by subscript a,b, and c respectively.A. Current in the loop 1, 2, and 3 due to inductiveThe voltage induced in loop 1, 2, and 3 analytically obtained as:By solving the circuit model shown in Fig. 3 and 7 and from (8), the inductive current flowing through loops 1, 2, and 3(subscript M represent magnetic current and LI, L2, and L3, represent three loops) for solidly grounded, grounded with SVL and proposed method type of bonding obtained as:B. Current in the joints due to capacitive effectBy solving the circuit model in Fig. 4, the capacitive current through different ST and CB joints for a solidly grounded cable system is obtained as (subscript C describes the capacitive current and ST and CB describe the cross-bonded and straight-through joints):Similarly, for grounded with SVL system, the capacitive current through different joints are analytically obtained as:From Fig. 7, the capacitive effect current, flowing through different joints for the proposed method obtained as:Therefore, the total current flowing in the particular joints is the sum of the capacitive effect current in the particular joint and the inductive effect current flowing in the particular loop.Ill) Mathematical modelling of standing voltage in the joints for different types of bondingSimilar to the methods in Section in, the voltage in the joints due to inductive and capacitive effect for different types of end bonding and obtained as:A. Voltage in the joints due to inductive effectThe standing voltage between the ST joints 1, 2, and 3, and between the CB joints 1-6 due to inductive effect is same for three different types of end bonding and obtained by solving Fig.3 and 7and represented as:However, the standing voltage in the last set of ST joints are different for different bonds ending and represented as:B. Voltage in the joints due to inductive effectSimilar to the current method, the capacitive effect of voltage in the ST and CB joints for a solidly grounded cable system are obtained as:Similarly, for grounded with SVL system, the capacitive effect of voltage across different joints are analytically obtained as:Similarly, for the proposed method, the capacitive effect of voltage across different joints are analytically obtained as:The total voltage in each joint for a particular type of bonding is the sum of voltage produced by both the capacitive and inductive effects for the particular joint.IV) Working Example and Simulation on the tested cable

[0023] Two Steady-state experiments for three types of bonding compared with original case study are performed on HAVELLS three-core, XLPE insulated material, with an inner conductor (aluminum) area of 35mm2, outer grounded sheath diameter of 7.35mm, the radius ofthe metallic sheath is 1mm, and insulation relative permittivity of 2.3. The cable is laid in a trefoil formation with rcsand rssas 8cm and 10cm respectively. In the original case, the first minor section of the cable is 5m, second minor section of 5.5m and third minor section of 5.2m. Two different case studies are considered to verify the analytical results. In the first case, the third minor section is 3m in length and in the second case study, the third minor section is 7m. The current and voltage at different joints are compared for different types of bonding (10). The grounding resistance is kept at 0.2Q, while to portray SVL, a 10 Mega-ohm resistance was used. The cable is supplied with a three-phase voltage (11) of 440V and a load current of 15 A, while the power factors for the three phases are 1, 0.98, and 0.85. The current and voltage in different joints for all three types of end bonding methods are measured using a FLUKE 17B digital multimeter (12) whose uncertainty in measurement is 1.5% as shown in Fig. 9.

[0024] Apart from the experimental cable, which was of limited length, voltage, and current supply, the simulation for three types of bonding compared with original case study was performed on MATLAB SIMULINK. The operating voltage and current in the simulated cable are 220kV and 550A, while the power factors for the three phases are 1, 0.98, and 0.85. The cable is insulated with XLPE material with a relative permittivity of 2.3 and thickness of 27mm. The conductor radius is 21mm and the metallic sheath is 6mm. The cable is laid in a trefoil formation with rcsand rssas 85cm and 115cm respectively. The value of grounding resistances is 0.2Q. In the original case, the first minor section of the cable is 500m, second minor section of 550m and third minor section of 520m. Four different case studies are considered. In Case I -IV, the length of the third minor section is considered as 150m, 300m, 650m, and 800m respectively. A transient case study was also considered in simulation for Case IV, where the peak voltage and current are simulated for the conductor to sheath fault at four different places in the major section. The faults are created in the first phase, at distances of 5m, 495m, 1030m, and in 1800m. The peak voltage and current are observed just near the ST and CB joints. The fault has a duration of 0.3s.

[0025] This section was further divided into two subsections, in the first subsection results regarding the practical case study in the laboratory were reported. The second case study was about the simulated cable, performed in MATLAB Simulink.A. Practical Case StudyPractically obtained rms current and voltage for two different case studies and three different types of bonding compared with the simulation and analytical results are shown in Figs. 10 to 21.From Figs. 10 to 21, it is observed that case II has the maximum current and voltage across different joints. In Table I, the maximum value of current and voltage for case II is compared with different joints and types of bonding.TABLE I - Comparison of practical maximum current and voltage

[0026] In Table I, (1) and (2), represents comparing the proposed method with the solid grounding and grounding with SVL respectively. The current in the second set of ST joints in the proposed method only exceeds the grounded with SVL case by 0.002mA (can be treated as almost the same) margin except that for both ST and CB joints, the proposed method shows a better voltage and current profile compared with other end bonding methods.

[0027] Similarly, the maximum rms current and voltage at different joints for case II are also compared with original case study and is shown in Fig. 22 and Fig. 23. It is observed that, except the peak rms voltage at the last set of ST joints (within the limits of 50V), the voltage and current profile is even better for the proposed method when compared with the original case.

[0028] The analytically obtained values of RMS current and voltage in the joints match with a minimum accuracy of 99.87% when compared with the practical results. Also, from the practical, simulation, and analytical results it is observed that the rms value of current and voltage is minimum for the proposed method when compared with the solid grounding or grounding with SVL even during the unbalanced loaded condition. During steady state operation, the current in the joints in the proposed end bonding method shows better profile evenwhen compared with the original case study. The voltage also in the joints remains under 50V. This happens because due to the presence of SVL, the circulating current in the sheath is in check, and the voltage across the joints is minimal due to connecting the sheath terminals of the three phases together.B. Simulation Case Study

[0029] The Simulated RMS current and voltage for four different case studies and three different types of bonding compared with the analytical results are shown in Figs. 24 to 47.

[0030] From the simulation results presented in Figs. 48 and 49, the maximum rms current and voltage occurring in each set of ST and CB joints is considered for different third minor section lengths, and compared with different end bonding techniques.

[0031] From Figs. 46 and 47, it is observed that case I has the maximum current and voltage across different joints. In Table II, the reduction in the maximum value of current and voltage for the case I simulation of the proposed method and the other two types of bonding is presented.TABLE II - Comparison of simulated maximum current and voltage

[0032] In Table II, (1) and (2), represents comparing the proposed method with the solid grounding and grounding with SVL respectively. It is observed that the voltage across any joints does not exceed 50V. The current in the second set of ST joints in the proposed method only exceeds the grounded with SVL case by 1.08 A margin (can be treated as almost the same.Except for both ST and CB joints, the proposed method shows a better voltage and current profile compared with other end bonding methods.

[0033] Similarly to the practical study, the maximum rms current and voltage at different joints for case I are also compared with original case study and is shown in Fig. 50 and Fig. 51. It is observed that, except the peak rms voltage at the last set of ST joints (which remains within limits of 50V, according to standard), the voltage and current profile is even better for the proposed method when compared with the original case.

[0034] The peak RMS transient current and voltage for case IV, in different joints and end bonding method and original case study is shown in Fig. 52.

[0035] From the steady-state simulation, it is analyzed that the simulation and analytical result match with a minimum accuracy of 99.92%. Also like the practical case study, whatever the length of the third minor section, the proposed method of end bonding is the most effective in terms of RMS current even during the steady state unbalanced loaded condition when compared with the original case study also the voltage in the joints remains under 50V for the bonding method disclosed in the present invention. In Fig. 48, represents 2m from the particular joints. Even during the transient case as shown in Fig. 48, the proposed method always has the lower value of peak voltage and current when compared with the other methods of bonding and original case study.

[0036] While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope of the invention as claimed.

Claims

E CLAIM:

1. A method for mitigating circulating currents and voltages in the sheath of cross bonded cable with non uniform cable length comprising: a) identifying the last set of cable joints, where these joints typically mark the end of a minor section; b) associating the link box within these last set of cable joints wherein the sheath terminals of all the joints are connected together to form a common terminal point; and c) coupling the common terminal formed by the connection of the sheath terminals of the last set of cable joints to a special voltage limiting device (SVL).

2. The method as claimed in claim 01, wherein the sheath voltage limiter (SVL) is configured to maintain the voltage across different parts of the cable sheath within a standard range of 50V.

3. The method as claimed in claim 01, wherein the cable comprises a plurality of straight through (ST) joints.

4. The method as claimed in claim 01, wherein the special voltage limiting device (SVL) acts as an open circuit under steady state conditions and solidly grounded during transient conditions.

5. The method as claimed in claim 01, further the method comprising the step of selecting a special voltage limiting device (SVL) having an impedance configured to maintain a voltage across different parts of the cable within a predetermined safe range.

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