小电阻接地系统的继电保护原理
The principle of relay protection for small resistance grounding system
对于小电阻接地系统, 当电网发生单相接地故障时, 由于人为地增加了一个与电网接地电容电流相位相差90°的有功电流, 流过故障点的接地电流就等于电容电流和有功电流的相量和。应该说, 根据零序电流或电阻性电流的大小和方向也是很容易区分故障支路和非故障支路的。
For a small resistance grounding system, when a single-phase grounding fault occurs in the power grid, a active current is artificially increased by 90 degrees with the phase difference of the capacitance current of the power grid. The grounding current passing through the fault point is equal to the phase amount of the capacitance current and the active current. It should be said that according to the magnitude and direction of zero sequence current or resistive current, it is easy to distinguish fault branches from non fault branches.
由于单相接地时故障电流大, 必须切除故障线路, 故其保护配置可为: 限时(瞬时)电流速断保护, 低电压闭锁过流保护, 两段式零序保护, 所有保护均作用于跳闸。对于架空输电线路, 应配置一、二次(或多次)自动重合闸,使得瞬时性故障后可尽快恢复供电, 同时在永久性故障时, 加速继电保护动作于跳闸；对于电缆输电线路, 考虑其故障必定是永久性故障(或永久性故障所占故障比例很大) , 故不必设置自动重合闸。另外, 为保证可靠地切除故障线路, 保护一次设备的安全, 考虑到故障线路的保护或开关存在拒动的可能, 所以应在中性点接地电阻回路中加装电流互感器(TA) ,接入零序后备保护(或称接地电阻零序保护) , 加适当延时后,作用于跳开变压器低压侧开关。
Because of the large fault current in single-phase grounding, the fault line must be removed, so its protection configuration can be: time limit (instantaneous) current quick break protection, low voltage locking overcurrent protection, two phase zero sequence protection, all protection action on tripping. For overhead transmission lines, one or two (or multiple) automatic reclosing should be configured so that the power supply can be restored as soon as possible after the transient failure. At the same time, in the case of permanent fault, the acceleration relay will act on the tripping; for the cable transmission line, the fault must be a permanent fault (or a large proportion of the permanent faults). Therefore, it is not necessary to set automatic reclosing. In addition, in order to ensure the reliable removal of the fault line and protect the safety of the first equipment, considering the protection of the fault line or the possibility of the switching of the switch, the current transformer (TA) should be installed in the neutral grounding resistance loop, and the zero sequence backup protection (or the ground resistance zero sequence protection) is connected, and the appropriate delay is applied to the jump. Transformer low voltage side switch.