Analysis And Solution Of CT Dead Zone In 500kV Open Substation

Conventional open substation takes into account the area and economy.When CT is configured on one side of the circuit breaker,the connection between the circuit breaker and the CT is not protected.If there is a fault between the circuit breaker and the CT,the protection can not be quickly removed at this time.If a circuit breaker and a CT dead zone failure occurs in the DC UHV transmission and receiving power grid,the excise failure time will exceed 400 MS,which will cause the UHV converter valve to continue to fail in phase conversion or decrease in power,and the success rate of both the delivery and the two ends of the power grid will be unbalanced,triggering grid oscillation,It has even led to destabilization.Through the system calculation,Henan Power Grid has a total of 500 kV substation failures in the five 500 kV substations of the Jinjia,Weihe,Xiangfu,and Baihe,resulting in continuous phase conversion failure or power drop of UHV DC,and even caused UHHV.DC transmission,may be stably destroyed by the power grid at both ends.Therefore,in order to ensure the safe and stable operation of the Central China Power Grid,it is particularly important to study the protection dead zone of the conventional substation in the area.This paper first introduces the damage of the dead zone of the 3/2 circuit breaker connection to the power grid and the current research situation at home and abroad.This paper describes how to form a fault analysis and solution for dead zone protection and dead zone protection,and puts forward two solutions to the situation of dead zone protection for the connection of 3/2 circuit breaker.1.Install a optical CT program.The optical CT is installed on the other side of the single-CT circuit breaker.The optical CT adopts a triple-redundant configuration,which is different from the conventional CT.The circuit breaker differential(failure)protection is configured according to the string,and the relevant circuit breaker is directly jumped in the event of a failure.At the same time,increase the number of stations.Fast communication channel,Realize the rapid removal of the station breaker.The dead zone failure of this scheme is expected to be excised within 110 ms,and the failure of the circuit breaker is expected to be excised within 200 ms.2.Adopt a comprehensive discrimination scheme for multi-interval information in the station.Collecting multi-interval voltage current information at this station,introducing voltage criteria,using the characteristics of rapid voltage return after fault removal,overcoming the influence of CT tail on current criteria,shortening the dead area or failure protection fault discrimination time,and increasing the number of fast communication channels between stations.Realize the rapid removal of the station breaker.The dead zone failure and circuit breaker failure of this scheme are expected to be excised within 200 ms.Then the paper selected the least influential in the case of the change of the above two schemes to carry out the pilot.The problem is solved by adding the optical CT on the other side of the single-CT circuit breaker,which is different from the conventional CT and using the multi-interval information comprehensive discrimination in the station.In this paper,the dead zone protection of circuit breakers in Henan power grid is studied by means of theoretical analysis.The results obtained are of practical significance to the safe operation of Henan power grid.