An insulation co-ordination procedure for power system equipment

Thesis Abstract

Generally, for existing Insulation co-ordination studies the power system has been modeled either by deterministic mathematical techniques or by statistical methods. The shortcoming of the existing conventional mathematical technique of Insulation co-ordination analysis is that it assumes that the power system dynamics is linear. This makes analysis of over voltage response of the system under transients less optimal for determining over voltage withstand of system elements. Thus, this work seeks to model a lightning induced over voltage transient in a High voltage power system substation(132/33KV) used as a case study) using Hidden Markov Model, to determine the maximum likelihood lightning surge signal. The station data and configuration was modeled/simulated (in a MATLAB environment), which implements the algorithms used in the work. The Hidden Markov algorithm(which makes use of observable parameters to study what is happening at the hidden states), was used to formulate the problem, while the Baum-welch and Viterbi algorithm were used to find/identify the maximum likelihood lightning overvoltage waveform. These hidden states are represented with different scenarios introduced in the work and the waveform identified, is used to determine the Basic Insulation level(BIL), which is used to determine other parameters accurately, which in turn helps to ensure an optimal/novel Insulation coordination procedure for power system equipment in the station. The results showed that the minimum required margin(15%) exceeded by a little value(i.e. about 1.08) and the evaluation carried out to raise the protection margin to 18% meant the relocation of the arrester to within 5.56m of the transformer.