Automatic Reclosing for Isolated Neutral Electric Grid Under Single-phase to Ground Fault

2020;
: pp. 1 - 7
1
Lviv Polytechnic National University
2
Lviv Polytechnic National University
3
Lviv Polytechnic National University
4
Lviv Polytechnic National University

6–35 kV electrical networks operates with isolated or compensated neutrals. Such mode of a neutral is the reason of emergence of considerable overvoltage in an electrical network during single- phase ground fault (SFGF), especially during short-circuit through an arc and various ferro-resonance phenomena. These overvoltage destroy the insulation of the electrically coupled network. Therefore, in order to increase the performance efficiency of the 6-35 kV network, it is necessary to minimize the operate time of overvoltage that are detrimental to the insulation of the network (especially cables). For this purpose it is necessary to use protections, which with minimum time delay disconnect feeder with SFGF. In order to reduce the time of de-energizing of consumers who have been disconnected by the protection during the SFGF, it is advisable to use automatic reclose (AR), which will lead to reduction of losses from electricity sacrifice. The AR automatically switches on an electic network element previously disconnected during the SFGF.

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To test the performance of the device created a physical model of the isolated neutral system, which allows to simulate SFGF. To protect against SFGF in the physical model used serial device “Altra”, which is successfully operated at various power facilities in Ukraine - power, thermal power stations, substations of enterprises and more. The mutual operation of protection devices during SFGF and AR has been tested on a physical model. Various modes during SFGF in the electrical network (damage in different places of the electrical network) and different nature of SFGF (short-term with self-liquidation, stable without self-elimination) were simulated. The analysis of the results  of  the physical model verification confirmed the high efficiency of the integrated use of the protection devices during SFGF and AR in the isolated neutral system and compensated network. The device is currently being piloted at one of substations of “Lvivoblenergo”.

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