Repeated ground protection circuit

In a three-phase four-wire power supply system, when the grounding resistance of a single grounding body cannot meet the requirements, multiple grounding bodies are often connected in parallel to
connect the neutral line to the earth at multiple places, which is called repeated grounding. The grounding resistance of repeated grounding bodies is not equal to the parallel value of the grounding resistance
of     each grounding body due to the shielding effect between grounding bodies . Repeated grounding resistance is below 10fl.     Repeated grounding can avoid electric shock voltage caused by neutral line interruption, and reduce the ground voltage and electric shock risk caused by shell leakage. -     When using protective grounding - in addition to the neutral point grounding of the system, grounding must also be carried out at one or more places on the neutral line. This is called repeated grounding, as shown in the figure. In a 220/380V three-phase four-wire power supply system with     the neutral point directly grounded , the neutral line is required to be grounded repeatedly. If repeated grounding is not adopted , when the neutral line is disconnected, the zero-connection button after the disconnection point is equivalent to neither connecting to zero nor grounding. Due to the unbalanced three-phase load and the asymmetry of the three-phase load voltage, the load neutral point voltage is not zero, that is, there is a certain dangerous voltage on all zero-connected equipment shells after the disconnection point ; when a person touches the equipment shell At this time, the working current will flow to the earth through the human body.     If a piece of equipment encounters a phase wire collision, the protective appliance will not operate because there is no neutral circuit , and phase voltage values ​​will exist for a long time on all zero-connected shells after the disconnection point ; when a person touches the outside of the equipment, the short-circuit current It will flow to the earth through the human body, which is very dangerous. If the grounding is repeated at one or more places, even if the neutral line is occasionally broken, the shed line will hit the shell, and the short-circuit current will form a loop with the system through repeated grounding. Activate the protective appliance.