Chae-Kyun Jung

A study on the fault location algorithm on underground power cable system

In this paper, we are going to propose the new algorithms to detect, classify, discriminate the transient and the reflected signal from noise and thus discriminate the fault section and locate the fault accurately on underground power cable system. Actually, at this system, its very difficult to discriminate the transient because of the reflected signal including many noises. Therefore, how to solve the noise interference is a big problem. In this paper, authors present a solution based on multiple scales correlation of the transient using stationary wavelet transform. Its simple, quick and straightforward. For applying all algorithms, we just use the signal captured in single end.

A Study on Lightning Overvoltage Characteristics of Grounding Systems in Underground Distribution Power Cables

This paper investigates the transient characteristics of grounding systems used in under-ground distribution power cables. Recently, two kinds of grounding system are used for underground distribution cables in Korea. The first one is conventional multi-point grounding system, the other is newly proposed non-bundled common grounding system. The non-bundled common grounding system has an advantage the decreasing the power loss due to decrease of the shield circulation current. In this paper, the lightning overvoltage induced in neutral wire (in case of non-bundled common grounding system, overvoltage between opened neural wires and grounding in each phase) of these two kinds of grounding systems are estimated and compared by field tests and EMTP simulations. The EMTP simulation methods are firstly verified by comparison of measurement and simulation. Finally, the insulation level against lightning is expected by EMTP simulation results using verified model.

Characteristics and Reduction of Sheath Circulating Currents in Underground Power Cable Systems

Sheath current can cause sheath loss and reduce the permissible current of a power cable transmission system. High sheath current is usually caused by mixed cable burying formation, different length between sections, poor connection of the bonding leads, and connection of distribution cable onto transmission systems. This paper analyses the characteristics of sheath circulating current at various conditions and presents a useful method to reduce it in a mixed burying formation system. It can effectively reduce the current by up to 90%. The method is validated by practical measurements and simulations using ATP, and has been implemented in actual systems. In addition, a special equipment is designed to measure and analyze the sheath circulating current. It can measure and analyze nine currents at a same time.

Fault location algorithm on underground power cable systems using noise cancellation technique

In previous paper, the noise cancellation technique was introduced to identify the reflective waves for fault location in noisy environment. This technique was based on the correlation of wavelet coefficients of stationary wavelet transform at multi scales. This paper describes how to apply it for fault location on underground power cable systems. The fault location algorithm is tested by simulation on real power cable systems. Simulation results proved it can detect and locate in very difficult situations.

Sheath current characteristic and its reduction on underground power cable system

Sheath current causes the sheath loss and can reduce the permissible current of the power cable transmission system. High sheath current is usually caused by the mixed burying formation of the cable, different length between sections, poor connection of the bonding leads, and connection of distribution cable on the transmission system. This paper analyses the characteristics of the sheath circulating current at various conditions and presents a useful method to reduce the sheath current in a mixed buying formation system. It can effectively reduce the current by up to 90%. The method is validated by the practical measurements and simulation using ATP, and also adopted in actual system. In addition, a special equipment is designed in this paper to measure and analyze the sheath circulating current. It can measure and analyze nine currents at a single time.

Technical Review on Parallel Ground Continuity Conductor of Underground Cable systems

Abstract – The Induced sheath voltage is significantly increased at single point bonding section when the ground fault occurs on power cable system because there is no return path of fault current. For solving this problem, therefore, many researchers recommend the PGCC (Parallel Ground Continuity Conductor). In this paper, the characteristics of PGCC are extensively analyzed for reducing the level of induced sheath voltage at the single point bonded section for Korea underground power cable system Keywords: Parallel ground continuity conductor, Overvoltage, Underground cable 1. Introduction Generally, single point bonding section consists in arranging for the sheaths of the three cables to be connected together and earthed at one point only. In Korea, in each single point bonded section, the SVL (sheath voltage limiter) units should be connected between the unbounded ends of the cable sheaths. In this section, during a ground fault, the zero sequence fault current carried by the cable conductor cannot return by any path because single point bonded cable sheath is ground at one position only or the sheaths are separated by SVLs. Specially, the induced sheath voltage is significantly increased at this point when the ground fault occurs on power cable system because there is no return path of fault current. For solving this problem, therefore, many researchers recommend the PGCC (Parallel Ground Continuity Conductor) in single point bonded section. The PGCC is very effective for suppressing an induced sheath overvoltage because of providing an external fault current path. Accordingly, a single point bonded cable installation with PGCC which is earthed at both ends of the route is recommended. The spacing between PGCC and phase conductor should be closed to limit the voltage level during a single phase ground fault. The size of PGCC should be also adequate to carry the full expected fault current for the cable system. However, in Korea, the PGCCs are not applied for single point bonded section till now. The sheaths are just separated by SVLs. Recently, the installed SVLs in single point bonded section were exploded by single line to ground fault, which caused heavy damage to joint box. Therefore, in this paper, the characteristics of PGCC are extensively analyzed for reducing the level of induced sheath voltage at the single point bonded section for Korea underground power cable system. Firstly, the optimal installation section is estimated by evaluating of economical and technical efficiency. Next, the adequate conductor size of PGCC will be decided by maximum fault current considering an expected maximum circuit breaker capacity. The additional various cases are also considered including the dimension and the position of PGCC, spacing between PGCC and phase conductors, faulty phase, cable construction types and two PGCCs usage. Korea electric power company, KEPCO, has now plan for adopting PGCC which is suitable on Korea underground power cable system based on the results of this paper. Accordingly, the PGCC will expect to be applied on real power cable system in Korea, and it also contributes to safety service.

Sheath Circulating Current Analysis of a Crossbonded Power Cable Systems

The sheath in underground power cables serves as a layer to prevent moisture ingress into the insulation layer and provide a path for earth return current. Nowadays, owing to the maturity of manufacturing technologies, there are normally no problems for the quality of the sheath itself. However, after the cable is laid in the cable tunnel and is operating as part of the transmission network, due to network construction and some unexpected factors, some problems may be caused to the sheath. One of them is the high sheath circulating current. In a power cable system, the uniform configuration of the cables between sections is sometimes difficult to achieve because of the geometrical limitation. This will cause the increase of sheath circulating current, which results in the increase of sheath loss and the decrease of permissible current. This paper will study the various characteristics and effects of sheath circulating current, and then will prove why the sheath current rises on the underground power cable system. A newly designed device known as the Power Cable Current Analyser, as well as ATP simulation and calculation equation are used for this analysis.

Analysis of Frequency Response Characteristic Considering Semiconducting Screen in Underground Distribution Cables

This paper describes frequency response and propagation characteristics considering semiconducting screen in distribution cables. In CIGRE WG 21-05, Simplified Approach(SA) and Rigorous Approach(RA) which can revise the permittivity considering semiconducting screen propose for more detailed EMTP model and frequency dependant analysis. In this paper, the frequency dependent characteristics of complex permittivity are variously analysed by cole-cole function of RA. The attenuation, propagation velocity and surge impedance according to frequency range(1 kHz to 500 MHz) and cable length are also analysed by SA and EMTP simulation in distribution cables. The propagation velocity considering semiconducting screen is slower, and it is saturated over the range of 1 MHz. The signal is significantly attenuated as frequency range is high.

Analysis on Lightning Overvoltage According to Lead Length of Surge Arrester for Underground Cable Outdoor Termination Protection at C/H Tower

This paper describes the lightning arrester transients in cable head termination. The installation references of cable head tower and lightning arresters are firstly reviewed, then the performance of lightning arrester operation is also evaluated based on lightning overvoltage analysis by the change of grounding lead cable length. This paper finally proposes the optimal length of grounding lead cable at the cable head termination. The limited lightning current is also proposed according to the change of grounding lead cable length. The results will contribute to protecting insulation breakdown failure against lightning surge at the terminations and joints.

Medium Voltage HTS Cable Thermal Simulation using PSCAD/EMTDC

This paper described the medium voltage high temperature superconducting cable thermal simulation and its application. New simulation method for HTS cable modeling using PSCAD/EMTDC is introduced in this paper. The developed simulation method consists of electrical model part and thermal model part. In electrical model part, power loss and thermal capacitance can be calculated in each layer, then the temperature of each layer can be calculated by power loss and thermal capacitance in thermal model part. This paper also analyzes the electrical and thermal characteristic in the case of normal operating condition and transient including single line to ground fault and line to line ground fault using new simulation method.