Sheath Fault Research Articles

Rectification of Sheath Faults Observed in Power Cables and Accessories in EHV Cable Circuits

Rectification of Sheath Faults Observed in Power Cables and Accessories in EHV Cable Circuits

Fault current calculation and grounding scattering optimization of 220 kV tunnel cable systems

Grounding faults in tunnel cables have received widespread attention. Establishing a fault model for tunnel cable systems in specific environments and proposing a fault current simulation method with high-speed computation and precise calculation accuracy is crucial for its stable operation. Additionally, optimizing grounding scattering method with better fault current scattering ability and conservation of land resources is of utmost importance. The metal sheath fault current of the tunnel cable is deduced using the double-sided elimination method. Based on the finite element method, three types of grounding scattering methods (i.e., spiral, cage and bearing platform) of working shafts are deduced. The ground surface potential of the working shaft is inferred with reference to human body safety limits. The result shows that the maximum cable sheath fault current reach 136.74 kA when the fault location is set at the beginning of the 1st major section. The cage grounding method effectively reduces the fault current density at the grounding point of the working shaft from 13,401.3A/m2 to 7192.8A/m2. When the number of vertical graphene conductors is increased to 6, the ground surface potential of the working shaft is 917.64 V, which is within the permissible range (955 V) for human body safety.

A Revised Model for Calculating HV Cable Sheath Current Under Short-Circuit Fault Condition and Its Application for Fault Location—Part 1: The Revised Model

This two-part paper proposes a revised method for calculating high voltage (HV) cable sheath currents, and for fault location of cross-bonded HV cable systems. The equivalent circuit and the cable impedance per unit length under short-circuit fault conditions are revised from those under non-fault conditions. Part 1 of this paper proposes a revised phasor domain mathematical model for the sheath current calculation under fault conditions, following demonstration that short-circuit faults can cause changes in the equivalent circuit of the cable metal sheath, and cause changes in the cable impedance per unit length. The calculation results, as given in a case study, show that there exists a unique relation between the fault position and the sheath fault currents, making it possible to locate a fault by analyzing the characteristics of the sheath currents during a fault. Part 2 of the paper focuses on the fault location method via sheath current monitoring.

Online Monitoring and Diagnosis of HV Cable Faults by Sheath System Currents

Cross-bonded metal sheath connection is applied in sectioned single-core power cables to reduce or eliminate the voltages that are induced in the sheath over long distances. However, cross-bonded cables present an opportunity as well as a challenge for online measurement and diagnosis of cable conditions. In this paper, a methodology to identify cable sheath faults through analysis of the sheath system currents in a cross-bonded cable system is presented. First, a numerical model is established to simulate the sheath currents in cross-bonded cable systems. Second, analyses of several faults, which happen frequently with serious consequences, are presented on the basis of current measurement at the link cable. Simulations of normal and fault conditions are given to determine the feasibility of fault diagnosis. A case study using field data from a cable tunnel in China considering the normal condition is presented to verify the numerical model. Results in normal condition show good consistency with field data with error less than 5%. Simulation results of fault conditions show that analysis of readings from six current sensors can distinguish different fault types and fault positions using the method proposed. Based on the analyses, criteria are established for sheath loop fault type diagnosis.

The Feasibility of Cable Sheath Fault Detection by Monitoring Sheath-to-Ground Currents at the Ends of Cross-Bonding Sections

This paper aims at checking the possibility that cable sheath faults in unipolar three-phase HV and extra HV cables with sheath cross-bonding systems can be detected by monitoring sheath-to-ground currents at the solid bonding ends of major cross-bonding sections. This goal is achieved by calculating such currents for some reference case studies of faults of the outer thermoplastic jacket in unipolar three-phase land cables for power transmission in flat formation. The case studies differ as to cable voltage ratings, resistance and location of the fault, symmetry of minor sections, and number of major sections. The results show that the aforementioned possibility does exist, particularly for some fault types and for sufficiently high cable load.

Sheath fault detection and classification based on wavelet analysis

AbstractThis paper presents a wavelet based algorithm to detect and classify sheath insulation faults on underground transmission cables. This algorithm can detect a high impedance sheath to earth fault, classify it, and discriminate it from other phenomena, such as load change, harmonics and surges on the cores. For the development of the algorithm, a simplified fault model is introduced to simulate a sheath to earth fault on a power transmission cable. Before applying wavelet analysis, an ‘adaptive noise cancelling’ (ANC) technique is used to extract the fault signal. Simulation studies are reported on a 300 mm2 concentric copper PVC insulated bonding lead. Copyright © 2006 John Wiley & Sons, Ltd.

Wave propagation characteristics on cross‐bonded underground power transmission cables and sheath fault location

AbstractIn this paper, a new method to locate the sheath fault on crossbonded power transmission cables is presented. This method utilises the transients generated by the fault and captured at both ends of the sections. On crossbonded power cables, there are six modes of waves travelling along the whole cable system and three are associated with the sheath. The waves travelling in mode 2 are used for fault location. The arrival times of the transients on both ends are localised by wavelet analysis. ATP simulations are used to test and validate the proposed fault location approach for typical power transmission cables.

Sheath Fault Characteristics and Modelling on Underground Power Transmission Cables

Sheath Fault Characteristics and Modelling on Underground Power Transmission Cables

Stevensite and Talc—Hydrothermal Alteration Products of Wollastonite

AbstractMagnesium-bearing hydrothermal solutions moving along channelways created by faulting in the Willsboro, New York, wollastonite deposit have effected the conversion of wollastonite to layer-lattice silicates. Alteration products sheath faults in wollastonite and may be divided into three gradational but regular zones: (1) least altered (fresh) country rock composed of wollastonite with minor diopsidic clinopyroxene and grossularite-andradite garnet; (2) moderately altered rock rich in montmorillonite; and (3) strongly altered rock composed predominantly of talc.X-ray diffraction, oscillating-heating X-ray diffraction, electron microscopy, infrared absorption, base exchange, and chemical analyses substantiate identification of the montmorillonitic alteration product, pseudomorphous after wollastonite, as stevensite. Stevensite, a trioctahedral magnesium montmorillonite, has been reported heretofore only in basaltic rocks where it has been formed by the action of magnesium-bearing solutions on pectolite. Pectolite and wollastonite have similar compositions and structures and may be similarly converted to stevensite in a magnesium-rich hydrothermal environment.Talc, the dominant mineral in the most intensely altered zone bordering the solution channelway, was formed by the continuing action of magnesium-bearing solutions on stevensite. Stevensite has a defect structure, i.e., a deficiency in the total number of ions in octahedral coordination. The addition of magnesium from hydrothermal solutions to the octahedral layer of stevensite converts this mineral to talc, concomitantly freeing interlayer cations and water.Stevensite is unstable and is converted to talc above a temperature of 275°C at water pressures of 690 bars. It is believed that hydrothermal alteration of wollastonite took place at temperatures near or below 275°C with stevensite forming in the cooler part of the reaction zone, and talc forming from stevensite at slightly higher temperatures nearer the solution channelway.

The factors influencing the use of pneumatic methods for the location of sheath faults in pressurized telephone cables

An expression, based on the classical Poiseuille equation for gas flow through capillary tubes, has been obtained to describe the passage of gas through non-coaxial telephone cables under steady-state conditions, and, for cables in this category, the factor governing the flow has been shown to depend upon the number, gauge and arrangement of the conductors. An approximation of the pressure gradient associated with a small rate of gas flow has been derived from this expression, and consideration has been given to the degree to which this limits the successful location of sheath faults by methods involving the direct establishment of the pressure gradient, the installation of pressure-sensitive contactors, rate-of-flow measurements and the use of flow-direction indicators.

Location of sheath faults in pressurized telephone cables

Location of sheath faults in pressurized telephone cables