The problem of system neutral grounding should be decided according to the anti-short-circuit ability of primary equipment and the requirements of relay protection. The y-type junction line of large transformer has a switch between its neutral point and the ground network. If the switch is closed, it is grounded. If it is separated, it is not grounded. The opening and closing of the neutral switch must be operated according to the command of system scheduling. The neutral point of the grounding system must have at least one grounding point.
2. If a transformer neutral point is grounded on both ends of the line, does not mean that the three phase short circuit, because when the system is balanced three-phase voltage, the neutral point is not grounding current, only the asymmetric fault or three-phase voltage imbalance occurs, is earth current zero sequence current on (professional), at this moment, the zero sequence current relay protection monitoring, when more than a specified value, Cut off the fault selectively based on logic.
3. Small current grounding system, mainly considering the short circuit resistance of a device is poor, in the neutral point and the ground point is connected with an inductive coil or resistance, on the one hand to limit the short circuit current, on the other hand can reflect the zero sequence current, so that the relay protection reliable action. It can be seen from here that limiting the role of zero sequence current, although it reduces the harm of short circuit to primary equipment, but also reduces the sensitivity of relay protection, calculation must be carried out to ensure that both aspects can be satisfied, is contradictory and unified.
4. In the diagram of a device junction, the group of transformers can not be drawn casually, and must be consistent with the actual situation.
This is a more popular explanation, if you want to understand, must have a more professional knowledge of electricity.
Wuhan Xinshengneng Technology Co., LTD
