Event under the auspices of the Ministry of Economy of Slovak Republic

Analysis of the functioning of the earth fault protection with active influence on the electrical grid

Alexander Ukraincev
Department "Electric stations and electric power system

*Vladimir Nagay
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI)

Ivan Nagay
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI) - «NPP «RELDON» Ltd

Sergei Sarry
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI)

Gennadij Chmihalov
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI)


     Last modified: 2017-03-29

Abstract
Currently, in the distribution grids the main directional earth relay and non-directional earth fault protection current zero-sequence are used for the single-phase earth faults. At the same time in the last few years it has been possible to observe the processes of introduction of protection for the earth fault into the distribution grids based on the principles of imposing a signal of an non-grid frequency on the zero-sequence current. Such protections are most effective in view of the practical absence of the need to grading for the earth fault in the external grid with respect to the protected feeder. The most promising is the use as a superimposed signal of a special form or frequency other than an grid frequency, generated by special device, through a voltage transformer or arc suppression coils.
The purpose of the analysis given in the article is to refine the options for designing such protections and then to propose the most effective scheme for their organization. A study was made of schemes of protection for earth fault based on systems with an impact on the electrical grid of various configurations and various complexity. The considered grids can be either with isolated neutral or with compensation of the capacitive current by means of a arc suppression coil, and should be equipped with voltage transformers with a secondary winding connected to an open-delta. When reliable protection from the earth fault installed in the schemes of electrical distribution networks, a unified system is formed selective protection of all connections from the earth fault, with the ability to trip damaged element. The presence of automatic transfer switch allows to carry out the uninterrupted operation of all consumers.
The article also focuses on the effectiveness of the protection for earth fault based on systems with active influence on the electrical network by the various signals. As an example, the method of superimposing an active component of a special form to a zero-sequence current by switching a low-resistance impedance in the voltage-transformer winding circuit is considered. Various options for designing such protections are presented: decentralized, distributed, individual and centralized by possible algorithms of operation with the use of absolute and / or relative measurement of the amplitude of the superimposed signal in the protected connections.

 

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