The leakage protector is used to effectively protect the direct and indirect contact of the low-voltage power grid, and it can also be used as the phase loss protection of the three-phase motor. It has single-phase and three-phase.
Since it takes the leakage current or the change of the neutral point-to-ground voltage as the action signal, it is not necessary to use the current value to set the action value, so the sensitivity is high, and the power can be effectively cut off after action to ensure personal safety.
According to the working principle of the protector, it can be divided into three types: voltage type, current type and pulse type. The voltage-type protector is connected between the neutral point of the transformer and the ground. When an electric shock occurs, the neutral point shifts to the ground to generate voltage, so as to make the protection action cut off the power supply, but because it protects the entire distribution transformer low-voltage network, It cannot be protected by grading, so the power failure range is large and the action is frequent, so it has been eliminated. The pulse type current protector is a sudden change in the phase and amplitude of the three-phase unbalanced leakage current when an electric shock occurs, which is used as an action signal, but there is also a dead zone.
At present, current-type leakage protectors are widely used, and there are two types: direct-action and indirect-action. The direct action type is that the action signal output directly acts on the release to make the switch off and power off. The indirect action type is to process the output signal through amplification, energy storage and other links to make the tripper act to trip the gate. Generally, the direct action type is an electromagnetic protector, and the electronic type protector is an indirect action type.
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