| Title |
A Study on Operation Algorithm of Protection Device for Single Line Short Circuit of GVT in Ungrounded System |
| Authors |
윤형익(Hyoung-Ik Yoon) ; 최성식(Sung-Sik Choi) ; 이후동(Hu-Dong Lee) ; 남양현(Yang-Hyun Nam) ; 노대석(Dae-Seok Rho) |
| DOI |
http://doi.org/10.5370/KIEE.2019.68.2.253 |
| Keywords |
Active current ; Charging current ; Detector for current comparator ; GVT ; Single line short circuit ; Ungrounded system ; Zero-sequence current |
| Abstract |
Generally, when a single ground fault in ungrounded system occurs, zero sequence voltage at 3rd winding of GVT(Ground Voltage Transformer) may be produced and then the system in which a ground fault occurred can be selectively blocked by the capacity of active current that drive the SGR(Selective Ground Relay) according to CLR(Current Limited Resistor) in GVT. On the other hand, the secondary distribution system of the industrial site with the large-scale facility using several high-voltage motors is composed of main and local transformers and GVT is installed at each transformer. However, if the internal fault including short circuit of 3rd winding of the GVT installed at local transformer occurs due to the aging of the protective devices, the circuit breaker in the local transformer does not operate and the circuit breaker in the main transformer operates, and then main and local distribution system can be blackout. To overcome these problems, this paper analyzes the characteristics of short circuit at 3rd winding of GVT and proposes an operation algorithm of protection device to prevent the whole system blackout. And also this paper implements a simulator for protection device on ungrounded system and presents a modeling of the simulator using PSCAD/EMTDC. As a result of simulation based on various scenarios, it is confirmed that the proposed algorithm is useful and practical to prevent the whole system blackout. |