Protection Function of Molded Case Circuit Breaker

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(1) Short circuit protection

Short-circuit protection is short-circuit instantaneous tripping. Attention should be paid to adjusting the setting value of protection in time after load changes to prevent too small setting value from frequent trips affecting the quality of power supply, or setting value excessive ambassadors DZ47-63 air switches whose lines and equipment can not be effectively protected.

(2) Overload Delay Protection

Overload delay protection refers to the danger of burning down the equipment when the load current exceeds the limit of the equipment. The protection device can cut off the power supply in a certain time. Overload has a process of heat accumulation, and protection action does not need to be too fast. For short-term overcurrent, protection should not be operated.

(3) Isolation function

Isolation function is to require the leakage current of circuit breaker after disconnection not to cause harm to people and equipment. After several short circuit trips, the performance of the switch decreases and the leakage current increases. For human body, the leakage current below 30 mA is safe. In harsh environment, the leakage current over 300 mA lasts for more than 2 hours, which may cause phase-to-ground short circuit of insulation damage and fire.

(4) Leakage protection

There are two kinds of leakage apparatus: thermal magnetic leakage apparatus and electronic leakage apparatus. Compared with electronic leakage apparatus, electronic leakage apparatus has the advantages of small size, high precision and high sensitivity, but its anti-interference ability is poor. At present, electronic leakage protector occupies the mainstream. When the leakage current reaches the setting value, the executive circuit receives the induction voltage signal of the secondary side of zero sequence current transformer, drives the conversion contacts to output the leakage protection signal, so that the trip action cuts off the power supply.

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