Numerical analysis of transients in the zero sequence circuit networks of auxiliary TPP

Authors

DOI:

https://doi.org/10.15802/etr.v0i9.51728

Keywords:

ferroresonance, the circuit of zero sequence, single phase ground fault, stochastic modeling, spectral analysis, the probability distribution function, probability density function

Abstract

The reliability of the network's auxiliary of thermal power plants determines the performance of a complex technological cycle, which is the production of electricity. Emergency turning off of mechanisms of auxiliary reduces the power delivered to the network from generators, and it sometimes requires a full load dropping and turning off of the generator. The main consumers of auxiliary are high-voltage engines, whose damage most frequently begins with the appearance of a single-phase earth fault.

The purpose of the article is a study of transients in the zero sequence circuit networks of auxiliary of thermal power plants, revealing the features of the flow of these processes, the factors affecting the resulting arc overvoltages. In order to study transients it is used the mathematical model created in the package MATLAB/Simulink. Parameters of voltage transformer (VT) are determined experimentally.

The results of studies showed that in networks with earth fault current about 5 A it’s possible occurrence of ferroresonance phenomenon. The domain of existence of steady ferroresonance depends by the number of parallel working VT. In this case the domain of existence of subharmonic ferroresonance corresponds to the capacity of network 0,085-0,62 μF related to one VT. The processes of single-phase arc fault taking into account the stochastic behavior of the grounding arc were investigated. It is proved that the frequency rate of arc overvoltages is proportional to breakdown voltage. At the Gaussian distribution of breakdown voltage the frequency rate of arc overvoltages are also distributed Gaussian function. The operation modes of the microprocessor directed protection from single-phase ground fault in the arcing fault mode were investigated. It’s proved that the correct setting of this protection is able to act selectively in the unstable faults. Long-term direction of further theoretical and practical research in this area is the experimental determination of the frequency characteristics of the measuring current and voltage transformers and research of transients with the nonlinear properties of the measuring transformers.

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Published

2015-10-20

Issue

Section

Power Supply