城市轨道交通配电变低压侧中性点接地方案探讨

变压器中性点接地方式分为中性点直接接地及在低压配电柜内单点接地两种,具体采用何种方案,需根据低压配电系统的接地形式、低压进线及母联断路器的开关的极数决定。接地形式和进线及母联开关极数的选择又会影响低压进线断路器接地保护的配置形式以及PC级ATSE的断路器的极数选择,若ATSE断路器极数选择不当,可能会造成电气火灾装置的误报警。分析目前轨道交通常用的配电形式所存在的问题,并提出推荐方案:对于轨道交通低压侧采用单母线分段的接线形式,建议变压器中性点采用在低压柜内单点接地方案,进线和母联断路器的开关极数采用三极,进线断路器接地保护采用零序过电流保护原理,PC级ATSE的断路器采用四极形式或ATSE采用四极形式。

Neutral Point Grounding Scheme of Transformer of Urban Rail Transit

The neutral point grounding scheme of transformer has two schemes: direct grounding and single-point grounding in low voltage distribution cabinet. The specific scheme should be determined based on the grounding type of the low-voltage distribution system; and the pole number of the low incoming voltage of the circuit breaker and the bus switch. The selection of grounding type, number of bus switch, and line switch will affect the configuration of the grounding protection of the low voltage line circuit breaker and the pole number of the PC ATSE circuit breaker. If the number of poles of the ATSE circuit breaker is not properly selected, it may cause the electrical fire device to give a false alarm. This paper analyzes the problems existing in current distribution modes of rail transit and proposes a recommendation scheme. For the low voltage side of rail transit with single bus segment connection, the neutral point of transformer should be a single-point grounding scheme in low voltage cabinet. Thus, the switch pole of the incoming line and the bus circuit breaker adopts three poles. The principle of zero-sequence overcurrent protection is therefore adopted for the earth fault protection of incoming circuit breakers while PC class ATSE circuit breaker adopts quadrupole type or ATSE adopts quadrupole type.