三相交流电力系统中性点与大地之间的电气连接方式,称为电网中性点成套装置接地方式。中性点接地方式涉及电网的安全可靠性、经济性;同时直接影响系统设备绝缘水平的选择、过电压水平及继电保护方式、通讯干扰等。一般来说,电网中性点成套装置接地方式也就是变电所中变压器的各级电压中性点接地方式。
The electrical connection method between the neutral point of a three-phase AC power system and the earth is called the grounding method of the complete set of neutral point equipment in the power grid. The neutral grounding method involves the safety, reliability, and economy of the power grid; At the same time, it directly affects the selection of insulation level of system equipment, overvoltage level, relay protection method, communication interference, etc. Generally speaking, the grounding method of the complete set of neutral point equipment in the power grid is the grounding method of the neutral points of the transformers at all levels in the substation.
我国110kV及以上电网一般采用大电流接地方式,即中性点成套装置有效接地方式(在实际运行中,为降低单相接地电流,可使部分变压器采用不接地方式), 这样中性点电位固定为地电位,发生单相接地故障时,非故障相电压升高不会超过1.4倍运行相电压;暂态过电压水平也较低;故障电流很大,继电保护能迅速动 作于跳闸,切除故障,系统设备承受过电压时间较短。因此,大电流接地系统可使整个系统设备绝缘水平降低,从而大幅降低造价。
In China's 110kV and above power grids, high current grounding is generally adopted, which means that the neutral point equipment is effectively grounded (in actual operation, to reduce single-phase grounding current, some transformers can be ungrounded). In this way, the neutral point potential is fixed at the ground potential. When a single-phase grounding fault occurs, the non fault phase voltage will not rise by more than 1.4 times the operating phase voltage; The transient overvoltage level is also relatively low; The fault current is large, and the relay protection can quickly trip and cut off the fault. The system equipment can withstand overvoltage for a short time. Therefore, a high current grounding system can reduce the insulation level of the entire system equipment, thereby significantly reducing the cost.
6~35kV配电网一般采用小电流接地方式,即中性点非有效接地方式。近几年来两网改造,使中、小城市6~35kV配电网电容电流有很大的增加,如不采取 有效措施,将危及配电网的安全运行。中性点非有效接地方式主要可分为以下三种:不接地、经消弧线圈接地及经电阻接地。
The 6-35kV distribution network generally adopts a low current grounding method, that is, the neutral point is not effectively grounded. In recent years, the renovation of the two power grids has significantly increased the capacitance current of the 6-35kV distribution network in small and medium-sized cities. If effective measures are not taken, it will endanger the safe operation of the distribution network. The non effective grounding methods for neutral points can be mainly divided into the following three types: ungrounded, grounded through arc suppression coils, and grounded through resistors.