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# Circuit models and simulations of surge attentuation on HV transmission system

Tong, Yu-Kwong (1989) Circuit models and simulations of surge attentuation on HV transmission system. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

## Abstract

Transient overvoltages occur in high voltage systems due to the operation of circuit breakers or disturbances such as faults and lightning strikes. These overvoltages will propagate through the system as surge voltages. The mechanism of the propagation is governed by two partial differential equations (telegraphers' equations). The surge will be attenuated and distorted due to energy losses when it travels along the system. The major energy losses under surge conditions are the ohmic and the corona losses. The ohmic losses in the conductor, the earth return and the cable sheath are frequency dependent. This thesis describes a method to develop an equivalent circuit model to cater for the variation of these ohmic losses in a single phase tranmission system during the surge period. Circuit elements of the model are determined using the skin depth theory and the accuracy of the approximation is dependent on the number of branches in the circuit model, the geometry of the system and the frequency bandwidth of the incoming surge. Investigations are caried out for steady state and transient response of the circuit models. The results are used to compare with the analytical derivations (Bessel functions, Carson's formula) and the field approach (PE2D' finite elment package). The corona loss is dependent on the system voltage. It is modelled by another circuit network consisting of a capacitor and a resistor connected in parallel. The dynamic values of the circuit elements are obtained using Peek and Skilling's equations which are inserted across the geometrical capacitance when the system voltage exceeds Vco and dV/dt> 0. The simulation of surge propagation is carried out using discrete pi' circuit networks. Long transmission lines are divided into short sections and each section is represented by an equivalent pi' circuit network. The complete transmission system is reconstructed by cascading these pi' networks together and the line losses are represented by using the appropriate circuit models. The simulated surge voltages using different transmission line models are presented and compared with published data of field tests. A comparison between simulations using the circuit model and single frequency skin effect (Bessel functions) and earth return (Carson's formula) correction is presented. The method is extended to simulate the surge propagation in a cable system under fast transients. Finally, a circuit model is developed for a ferrite choke surge attenuator and incorporated into the transient analysis program to investigate the amount of attenuation introduced by the choke.

Published date: 1989

## Identifiers

Local EPrints ID: 461192
URI: http://eprints.soton.ac.uk/id/eprint/461192
PURE UUID: d4bfa61f-1340-4923-9792-b3c75dc46ee4

## Catalogue record

Date deposited: 04 Jul 2022 18:38

## Contributors

Author: Yu-Kwong Tong