Design and construction of a new coaxial high voltage fast impulse current transducer

Since the introduction of zinc-oxide material in 1968 much research has been directed towards the characterisation of the electrical behaviour of the material under various stress conditions. An aim of some of these investigations is to achieve an equivalent circuit representation, which adequately simulates the observed test results. An adequate equivalent circuit representation will aid the reliable and efficient design of the overvoltage protection and help to improve the optimisation of the protective devices. A significant impediment to the accurate characterisation of zinc oxide has been the lack of reliable test data especially for fast-rate-of-rise impulses in the microsecond and sub-microsecond range. The measurement of current impulses in this range is highly influenced by the circuit arrangement and measurement transducer characteristics. In this work, a non-inductive coaxial current shunt was designed and constructed. The fast impulse tubular current shunt was based on the nickel chromium resistive material with a designed value of 5mΩ and 10kA current capability. The current shunt was successfully constructed except the nickel chromium material, which could not be successfully soldered to the aluminium casings. It is recommended that the work is to be completed in future projects

A new technicque for metal oxide surge arresters failure diagnostic using return voltage measurement

Due to their reliability and accuracy, many modern diagnostics based on dielectric voltage response, such as polarization/depolarization current (PDC), voltage decay (VD) and return voltage (RV) measurements, have been used in monitoring ageing processes of metal oxide (MO) varistors, which is the main part of a surge arrester. Among these diagnostics, recently, RV measurement (RVM) seems to be an increasingly popular method as it has high sensitivity to the condition of varistors and low sensitivity to disturbances in vicinity of the field measurements. Nonetheless, the basic interpretation based on the RVM essential parameters – peak RV, time-to-peak RV and initial slope of RV - provides insufficient information of the MO varistors condition since they are inevitably dependent on the measuring parameters such as the charging and discharging times as well as the test object temperature. Hence, this project focuses on a new way in interpreting the RVM parameters based on dielectric time constants analysis using an equivalent circuit of varistor microstructure, namely the Maxwell-Model. In order to investigate the ageing processes of MO varistors, two types of accelerated degradation techniques – impulse and heat degradations – are systematically conducted on test samples. Experimental results are presented and discussed in detail according to the underlying physical mechanism. On the basis of this concept, a sensible ageing parameter, p-factor, is used for better characterization of the ageing status of varistors

Induced Voltages on a Gas Pipeline due to Lightning Strikes on Nearby Overhead Transmission Line

The purpose of this paper is to investigate the severity of lightning induced voltages on a gas pipeline installed in parallel with overhead transmission line using two different simulation packages. The results from this study using CDEGS, which solves a given problem based on electromagnetic computations, reveal that the induced voltages on the pipeline are more accurate compared to that obtained by PSCAD simulation, which is based on the circuit approach. Unlike PSCAD, CDEGS considers many salient factors such as soil model, inductive, capacitive and conductive couplings, and multiple soil structures.  Models of a double circuit 132kV transmission line, gas pipelines, soil with different resistivities and variable lightning surges were developed. The effects of pipelines located at various heights above ground and distance of pipeline from the power lines were also studied. Compared to previously published work using PSCAD, it is found that CDEGS has given more accurate results. Several findings which were not possible using PSCAD were observed such as the effect of soil structure on induced voltage and multiple layers soil. This also led to better understanding of the conductive coupling from lightning strikes and fault conditions. The modeling work using CDEGS not only useful for providing more reliable data for further protection and mitigation techniques, but is  also very versatile to study the effects of various other important factors affecting the induced voltage on the pipelines.

Lightning Location and Mapping System Using Time Difference of Arrival (TDoA) Technique

Lightning strike is a dangerous natural phenomenon that can cause various problems. Telecommunication subscriber lines (TSLs) and electrical power lines are two systems that are almost always affected by nearby lightning strikes. Voltages in the telecommunication subscriber line (TSL) do get induced by nearby lightning strikes. The induced voltage can be carefully measured and lightning parameters such as the lightning current wave shape, lightning peak current and strike locations be reproduced. Better designs of lightning protection systems can be realised if data on lightning strike distribution in a given region is known. Commercial lightning mapping or locating systems are based on several technologies (Araujo, 2001; Kenneth, 2003). The two most popular methods are those based on the Time of Arrival (ToA) and the Directional Finder (DF) principles. An example of the lightning locating system (LLS) based on the ToA method is the country- wide LLS owned by the Malaysian national power company (TNB). The system is capable of determining the coordinates of the cloud-to-ground lightning strikes within 500m accuracy. However, for a localised distribution of lightning, say within 1 square km area, this accuracy is too large for the data to be meaningful

Condition Monitoring of Zinc Oxide Surge Arresters

Over voltages in power system may occur due to lightning, fault or switching operation. These overvoltages could reach dangerous amplitudes for power system apparatus. To protect the system electrical equipment and to guarantee an economic and reliable operation, surge arresters are applied in almost all types of electrical power network. Gapless zinc oxide (ZnO) surge arresters are widely used. The surge arresters are usually connected between the phase and ground terminals. They limit the voltage level in equipments such as transformers below the withstand voltage level

AC Interference on Gas Pipeline due to Phase to Ground Faults in Overhead Transmission Line

The purpose of this research is to investigate the severity of voltages induced on gas pipeline installed in parallel to a 115 kV overhead transmission line. The overhead transmission line (OHTL) is configured as a single-circuit. One of the phases exposed to single phase to ground fault. Transmission of high voltage along the same right of way (ROW) with metallic conductor may possibly introduce interference on metallic conductors such as gas pipeline (GPL) due to power frequency voltage as well as due to phase faults and switching phenomena. Two main approaches were used to compute the induced voltages, namely the method of moment (MOM), which is based on electromagnetic field theory, and circuit based method. The simulation considers the length of OHTL and GPL are 30 km and 10km respectively. The pipeline buried at 1 m underground in homogenous earth structure with various soil resistivites ranged from 10 to 1000 Ω-m. The transmission line consists of 150 towers and 200 m span length. The separation distance between the GPL and OHTL is varied from 5 to 100 m. The phase to ground fault current changed from 0.5 to 10 kA. Several observation points are made throughout the corridor, to examinant the induced voltages at different locations. The result show that, the soil resistivity, separation distance, and fault current had significant effect on pipeline induced voltage. In case of the observation points lying on the soil or on the outer surface of the pipeline coating, the induced voltage increased, when the soil resistivity increase, as expected. In case of the observation points placed inside the pipeline metal, and the pipeline is well coated, the induced voltage will decreased, when the soil resistivity increase

Integration of Frequency Dependent Soil Electrical Properties in Grounding Electrode Circuit Model

The effect of frequency dependent soil properties on the impedance and transient response of the grounding electrode was investigated. The frequency dependent soil models as proposed by Scott, Smith-Longmire, and Visacro-Alipio were critically reviewed. A novel method was proposed to integrate the frequency dependent soil electrical properties in the circuit model of grounding electrode. To validate the application of the method in circuit model, the voltage responses of the grounding electrode obtained by the circuit and electromagnetic models were compared. The voltage responses obtained by the circuit and electromagnetic models were in excellent agreement in terms of voltage peaks and wave shapes. The differences between voltage peaks obtained by the circuit and electromagnetic models were found less than 1%

Lightning generated electric field over land and sea at Northern Region of Peninsular Malaysia: Measuring Setup

Lightning is the transfer of significant charge between two charged object, it can appear between cloud-to-cloud, cloud-to-air and cloud-to-ground. All lightning activities are correlated with charge movement and therefore, it can be studied using measurement of electrostatic field (slow field changes), radiation field (fast field changes) and magnetic field affiliated with charge movement. The measuring equipment was a parallel flat plate and vertical whip antenna with an analog filter buffer circuit, connected to a digital high speed oscilloscope. In principle, both antenna have a similar measuring operation, with the exclusion of the antennas dimension, mode of transient recoder and the association of circuitry characteristic (decay time constant). This measurement setup are commonly used to perform electric field characterization related to various lightning events such as as preliminary breakdown, stepped leader, return stroke, subsequent return stroke, dart leader, dart-stepped leader, narrow bipolar pulses and cloud activity between strokes, such as regular pulse trains, K and M changes and chaotic pulse trains. The measurement systems are located very close to the sea, with respect in obtaining a perspicuous explaination of lightning propagation effects on sea instead on land. Noise-distorted effects in data captured usually introduce in a noisy environment or when the lightning strike far from the measurement station, thus the data gathered from the measurement need to be filter using MATLAB computer simulation before conducting further analysis. A promising wavelet 1-D technique, then, were used in signal denoising process rather using conventional filtration. In this works, the state of art in measuring vertical component of electric field focalized sea area during the thunderstorm days been demonstrate and explained

Modeling of time of arrival method for lightning locating systems

Various methods are used to locate cloud-to-ground lightning flashes. Even though a higher cost is incurred, a network of sensor stations is preferable to a single station due to the improved accuracy. For a single station measuring system, the accuracy of its analyses is mostly based on the chosen mathematical equations which can be solved in either linear or nonlinear mode. The sensitivity of the measuring equipment used is also particularly significant. This paper concentrates on the modelling of time of arrival (TOA) technique for locating a lightning flash by utilizing three broadband antennas. Consequently, by employing the developed model, the influences of geometric parameters on the accuracy of the model are evaluated. Therefore, a Matlab based simulation of the measuring system is developed. In the developed codes, randomly located lightning flash with its corresponding electromagnetic radiation was modelled. Results show that parameters such as lightning path shape, distance of the leader, and leader location can directly affect the accuracy of the TOA technique for extracting the azimuth and elevation

Polypropylene‐based nanocomposites for HVDC cable insulation

Cross-linked polyethylene (XLPE) is commonly used as an insulation material in power cables. Due to the recent advancements in the field of high voltage power transmission and distribution, there is a need for novel cable insulation materials that have high performance, recyclability and high working temperature as alternatives for the conventional XPLE-based insulation materials. Polypropylene (PP) shows excellent properties and has drawn considerable attention as a potential high voltage direct current (HVDC) insulation material. Therefore, the development of PP-based HVDC cable insulation with improved electrical, thermal and mechanical properties is important in discovering a potentially recyclable cable insulation material. Due to the remarkable development in the field of nanodielectrics, nanotechnology can be a promising solution for enhancing the overall dielectric properties of PP-based insulation materials. This review presents the important aspects of PP-based nanocomposites for HVDC cable insulation with a special focus on understanding the effects of various parameters of nanofillers on the dielectric properties of PP-based HVDC cable insulation. Based on the gathered information, future perspectives for improving the dielectric properties of PP-based nanocomposites for HVDC cable are provided