Selection of leakage circuit breaker
The leakage circuit breaker has two functions, one is the function of circuit breaker, the other is the function of leakage protection. The function of the circuit breaker is the same as that of the general low-voltage circuit breaker. The residual current is detected in the leakage protection part through the zero sequence transformer, that is, the change of the leakage current to the ground is judged by detecting the instantaneous value of the current of the phase line and the neutral line in the protected circuit. Therefore, the selection of circuit breaker, such as dz47le leakage circuit breaker, is the same as that of general low-voltage circuit breaker. Two basic conditions should be considered in the selection of the leakage protection function part (hereinafter referred to as leakage protector). One is that the leakage action current of the leakage protector must avoid the normal leakage current of the power grid; the other is that the leakage action current of the leakage protector must be less than the minimum ignition current or the human safety current that causes the fire, which is determined according to the main purpose of selecting the leakage protector. Generally, it shall be selected according to the following principles.
(1) The rated action current of the leakage protector shall be selected according to the provisions of the national standard gb13955-92 installation and operation of the leakage protector. The rated action current of the leakage protector shall be determined according to the normal leakage current of the electrical circuit, and the possible normal leakage current value of the protected circuit and equipment shall be fully considered. If necessary, the protected circuit can be obtained through actual measurement Leakage current value of circuit and equipment.
(2) The rated leakage non action current of leakage protector shall be selected according to the national standard installation and operation of leakage protector. The rated leakage non action current of leakage protector shall not be less than 2 times of the maximum value of normal leakage current of electrical circuit and equipment.
(3) Coordination between leakage current value of electrical circuit and equipment and leakage protection characteristics of graded installation
1) When it is used for a single electrical equipment, the operating current of the leakage protector shall not be less than 4 times of the measured leakage current in normal operation. To prevent electric shock and fire caused by leakage.
2) The operating current of the leakage protector of the distribution line shall not be less than 2.5 times of the measured leakage current in normal operation, and shall also meet 4 times of the leakage current in normal operation of the electric equipment with the largest leakage current. To prevent fire caused by electric leakage.
3) When used for the whole network protection, the action current shall not be less than 2 times of the measured leakage current. Add comprehensive leakage protection for the whole network to prevent fire caused by leakage.
(4) Generally, leakage protectors with different rated residual action current can be selected according to the following principles. For example, common model: DZ47LE-32
1) Leakage protector with rated residual action current of 30mA and below is used for the protection of direct contact and TT system; and the protection of non direct contact, it neutral line ungrounded system and fully exposed conditions (such as construction site, swimming pool, entertainment place, etc.).
2) Leakage protector with rated residual action current of 50mA and above is used for protection of non direct contact and TT system and fire prevention.
3) When the selective protection is configured, it shall be ensured that the non direct contact and TT system can be protected, and the leakage protection system with 30mA installed at lower level can also be protected selectively. Only isolate the accident circuit, and ensure the power supply of other circuits.
