(1) Function: Mainly used when personal electric shock or leakage occurs, can quickly cut off the power supply, protect personal safety, prevent electric shock accidents. Some leakage protectors also have overload and short circuit protection. They are used for starting and stopping motors frequently.

(2) working principle: in normal work, no matter whether the three-phase load is balanced, the sum of the three-phase current of the main circuit of the zero sequence current transformer is equal to zero, so there is no induction electromotive force in the secondary winding, and the leakage protector works in the closed state. If there is an electric leakage or an electric shock accident, the sum of the three-phase current is no longer equal to zero, and is equal to a current value of Is. The Is will form the loop through the neutral point of the human body, the earth and the transformer, so the zero sequence current transformer will produce the induction electromotive force corresponding to the Is on the two side, and add it to the tripping device. When the Is reaches a certain value, the tripping device moves the lock of the main switch and divides the main circuit.

(3) parameters and types

Parameters: rated current, rated leakage current, rated leakage action time.

Type: according to the action mode can be divided into voltage action type and current action type; according to the action mechanism, there are switching and relay type. According to the number of poles and lines, there are two, two, two poles, three lines, and so on.

(4) choice: choose leakage protector should be selected according to the purpose and operation conditions.

In accordance with the purpose of use:

(1) to prevent personal electric shock. Installed at the end of the line, use high sensitivity and fast leakage protector.

(2) use the sensitive and fast leakage protector in order to prevent the electric shock from being used in connection with the equipment.

(3) For the purpose of preventing fire caused by electric leakage and protecting lines and equipments, the middle sensitivity and delay type leakage protector should be selected.

According to the mode of power supply:

When protecting single-phase lines (equipment), single pole two wire or two pole leakage protectors should be selected.

2. When protecting three phase line (equipment), three pole products are selected.

3. When three-phase and single-phase are used, three pole, four wire or quadrupole products are selected.

5) method of use

(1) when selecting the pole number of the leakage protector, it must be compatible with the number of lines protected.

(2) check the leakage reliability after installation of the watt hour meter and fuse, and check regularly.