An investigation into 88 KV surge arrester failures in the Eskom east grid traction network

The Eskom East Grid Traction Network (EGTN) supplying traction loads and distribution networks has experienced at least one surge arrester failure over the past ten years. These failures results in poor network reliability and customer dissatisfactions which are often overlooked. This is because reliability indices used in the reliability evaluation of transmission and distribution networks are different. It is suspected that fast transient faults in this network initiate system faults leading to surge arrester design parameter exceedances and poor network insulation coordination. Preliminary investigations in network suggest that transient studies were not done during network planning and design stages. This may have resulted in the lack of surge arrester parameter evaluations under transient conditions leading to improper surge arresters being selected and installed in this network resulting in surge arrester failures that are now evident. These failures may also have been exacerbated by the dynamic nature of traction loads as they are highly unbalanced, have poor power factors and emit high voltage distortions. Poor in-service conditions such as defects, insulation partial discharges and overheating, bolted faults in the network and quality of supply emissions can also contribute to surge arrester failures. To address problems arising with different reliability indices in these networks the reliability of the EGTN is evaluated. In this work the reliability evaluation of the EGTN is done by computing common distribution reliability indices using analytic and simulation methods. This is done by applying the analytic method in the EGTN by assessing network failure modes and effects analysis (FMEA) when the surge arrester fails in this network. The simulation method is applied by applying and modifying the MATLAB code proposed by Shavuka et al. [1]. These reliability indices are then compared with transmission reliability indices over the same period. This attempts to standardize reliability evaluations in these networks. To assess the impact of transient faults in the surge arrester parameter evaluation the EGTN is modelled and simulated by initiating transient faults sequentially in the network at different nodes and under different loading conditions. This is done by using Power System Blockset (PSB), Power System Analysis Toolbox (PSAT) and Alternate Transient Program (ATP) simulation tools and computing important surge arrester parameters i.e. continuous operating voltage, rated voltage, discharge current and energy absorption capability (EAC). These parameters are assessed by in the EGTN by evaluating computed surge arrester parameters against parameters provided by manufacturers, the Eskom 88 kV surge arrester specification and those parameters recommended in IEC 60099-4. To assess the impact and contribution of in-service conditions, faults and quality of supply emissions in surge arrester failures these contributing factors are investigated by assessing infra-red scans, fault analysis reports, results of the sampled faulted surge arrester in this network and quality of supply parameters around the time of failures. This study found that Eskom transmission and distribution network reliability indices can be standardized as distribution reliability indices i.e. SAIDI, SAIFI, CAIDI, ASAI and ASUI indices are similar to Eskom transmission indices i.e. SM, NOI, circuit availability index and circuit unavailability index respectively. Transient simulations in this study showed that certain surge arresters in the EGTN had their rated surge arrester parameters exceeded under certain transient conditions and loading conditions. These surge arresters failed as their discharge currents and EACs were exceeded under heavy and light network loading conditions. This study concluded that surge arresters whose discharge currents and EACs exceeded were improperly evaluated and selected prior to their installations in the EGTN. This study found the EAC to be the most import parameter in surge arrester performance evaluations. The Eskom 88 kV surge arrester specification was found to be inadequate, inaccurate and ambiguous as a number of inconsistencies in the usage of IEEE and IEC classified systems terminology were found. It was concluded that these inconsistencies may have led to confusions for manufacturers during surge arrester designs and selections in the EGTN. The evaluation of fault reports showed that two surge arrester failures in this network were caused by hardware failures such as conductor failure and poor network operating as the line was continuously closed onto a fault. There was no evidence that poor in-service and quality of supply emissions contributed to surge arrester failures in this network. PSB, PSAT and ATP simulation tools were found adequate in modelling and simulating the EGTN. However the PSB tool was found to be slow as the network expanded and the PSAT required user defined surge arrester models requiring detailed manufacture data sheets which are not readily available. ATP was found to be superior in terms of speed and accuracy in comparison to the PSB and PSAT tools. The MATLAB code proposed by Shavuka et al. [1] was found to be suitable and accurate in assessing transmission networks as EGTN's reliability indices computed from this code were comparable to benchmarked Eskom distribution reliability indices. The work carried out in this research will assist in improving surge arrester performance evaluations, the current surge arrester specification and surge arrester selections. Simulation tools utilized in this work show great potential in achieving this. Reliability studies conducted in this work will assist in standardizing reliability indices between Eskom's transmission and distribution divisions. In-service condition assessment carried out in this work will improve surge arrester condition monitoring and preventive maintenance practices

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Production improvement in ACM manufacturing company using lean manufacturing approach

ACM Sdn. Bhd. is a manufacturing company, in which to continuously commit on improvement process which based on the fundamental goal, to minimize or eliminate waste while maximizing production flow. The purpose of this study is to develop a value stream mapping for a ACM Sdn. Bhd. and it was begin with creating a current state map and understand the production flow and the current cycle times. This provides the information needed to produce a future state map. The goal is to identify and eliminate the waste, which is any activity that does not add value to the final product, in the production process. In order to collect the information needed, the study was conducted within the production facility to enable the researcher gained knowledge and familiarized with the production flow and the activities being performed at the shop floor. Parameters such as cycle times, down times, work in process (WIP) for inventory and material, and information flow paths were recorded. This information will enable the researcher to visualize the current state of the process activities by mapping the material and information flow and looking for opportunities to eliminate wastes. ARENA simulation software package was used to simulate and analyze the process flow and times. Result from the analysis shows that there are areas where the ACM Sdn. Bhd. can further improve their production system. Improvements in cycle times of 13-22% are possible by new arrangement of the layout. The results can be used as a guide to the ACM for improvement and implement the lean manufacturing concept in their manufacturing system

A wireless system for monitoring leakage current in electrical substation equipment

In this paper, the design and the development of a remote system for continuous monitoring of leakage currents and ground currents in high voltage electrical substations are proposed. Based on wireless local area network technology, the system can be used to monitor continuously a variety of plants within the substation and has low power consumption with inbuilt overvoltage protection. It consists of a transmitter module equipped with a data acquisition (DAQ) system connected to leakage current and voltage sensors, and a receiver module connected to a remote controller for data processing and storage. The principle of operation and the characteristics of the various components of the system are described. Validation tests have been used to verify its performance in three different test situations: A) laboratory monitoring of the leakage current and voltage of a distribution surge arrester; B) laboratory measurement of the leakage current of an outdoor insulator; and C) field monitoring of the earth current and potential rise of high-voltage tower. The measured results are in close agreement with those recorded directly through a DAQ card with fiber-optic and coaxial cable connected systems. Data processing is carried out at the receiving end so that the monitored parameter is displayed continuously or at specified time intervals. The operation of the system has been tested and proved resilient under high-frequency interference signals such as those generated by corona and surface discharges

Simulation and Analysis of High Voltage Engineering in Power Systems

This book address important issues regarding the modelling and simulation tools and techniques that are applied in high-voltage engineering in modern power systems. The presented conceptual, constructive, empirical, experimental, and theoretical results are obtained in the area of high-voltage engineering. Special attention is given to protection methods against direct lightning strikes, partial discharge tests, discharges’ influence on different structures, cable screening, and induced voltages, among others

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

Simulation of switching overvoltages of 400 kV shunt reactor

Bam 400/132 kV substation in Kerman region, Iran, has a 50 MVAR shunt reactor on 400 kV busbar which is grounded through a 128 kVAR neutral reactor. The neutral earthing reactor assists in interrupting line to ground arcing current when switching for clearing a line to ground arcing fault, but the switching of shunt reactor which is grounded through a neutral reactor can impose a more severe duty on the circuit breakers than switching a solidly grounded shunt reactor. While opening shunt reactor, transient phenomena, such as chopping overvoltages and reignition overvoltage/overcurrents can occur. These overvoltages/currents can put circuit breakers, reactors and other equipment in danger. In this paper, the Bam substation’s equipment such as electrical circuits and associated equipment will be modelled in transient mode using EMTDC/PSCAD software. The arc behaviour and excessive voltage caused by the switching will be analysed. Finally, three methods including controlled switching, using surge arrester and a disconnecting switch across the neutral earthing reactor for mitigating these overvoltages will be compared

Simulation of switching overvoltages of 400 kV shunt reactor

Bam 400/132 kV substation in Kerman region, Iran, has a 50 MVAR shunt reactor on 400 kV busbar which is grounded through a 128 kVAR neutral reactor. The neutral earthing reactor assists in interrupting line to ground arcing current when switching for clearing a line to ground arcing fault, but the switching of shunt reactor which is grounded through a neutral reactor can impose a more severe duty on the circuit breakers than switching a solidly grounded shunt reactor. While opening shunt reactor, transient phenomena, such as chopping overvoltages and reignition overvoltage/overcurrents can occur. These overvoltages/currents can put circuit breakers, reactors and other equipment in danger. In this paper, the Bam substation’s equipment such as electrical circuits and associated equipment will be modelled in transient mode using EMTDC/PSCAD software. The arc behaviour and excessive voltage caused by the switching will be analysed. Finally, three methods including controlled switching, using surge arrester and a disconnecting switch across the neutral earthing reactor for mitigating these overvoltages will be compared

Degradation analysis of metal oxide varistors under harmonic distortion conditions

A thesis submitted in ful lment of the requirements for the degree Doctor of Philosophy in Electrical Engineering May 2016Modern electrical networks provide an opportunity for inevitable interaction between metal oxide arresters and power system harmonics. Therefore, these arrester devices are continuously exposed to the combined e ect of distorted system voltage and envi- ronmental thermal stresses. Recent studies supported by eld experiments have shown signi cant rise in the leakage current through these surge arrester devices when exposed to ac voltage with harmonics. However, the major shortcoming in the current knowledge and applications of varistor arresters resides on the reliability and the electrical stabil- ity of these overvoltage protection units, when subjected to long-term and continuous distorted ac voltage and thermal stresses from the environment. Commercially-sourced ZnO arresters of similar size and electrical properties are tested using standard ac accelerated degradation procedure or electro-thermal ageing test. The times to degradation, the coe cient of non-linearity, the reference voltages, as well as the clamping voltage measured are used to analyse the reliability and the electrical stability of the metal oxide-based arrester samples. The resistive component of the leakage current is extracted from the measured total leakage current. The three-parameter Weibull probability model is invoked in order to analyze the degradation phenomenon.MT201