Molded case circuit breaker is to contact, arcing chamber, trip and operating mechanism has been packed in a plastic shell, generally do not consider the maintenance, applicable to the branch protection switch, overcurrent trip with thermal magnetic and electronic type two kinds, the general thermal magnetic molded case circuit breaker is a selective circuit breaker, only overload long time delay and short-circuit transient protection, electronic molded case circuit breaker with overload long time delay, short circuit the short time delay, short circuit instantaneous and ground fault protection function. Some of the new products of electronic molded case circuit breakers have regional selective linkage. Most of the molded case circuit breaker is manual operation, and also some motor operating mechanism.
Molded case circuit breaker electromagnetic heat, most of them are the structure of circuit breaker, before is the use of electric heating and electric magnetic effect, thermal effect is to make use of bimetallic strip structure to implement switch current, big bimetallic strip bending deformation, deformation to a certain extent after push the switch tripping device, switch trip, through mechanical adjustment screw to adjust switch, thermal overload current adjustment accuracy is not high, belongs to the inverse time action, is the current, the greater the action time is shorter, some big switch such as electric circuit breaker.
Thermal overload current is not directly USES the bimetallic strip structure, but the use of current transformer, to convert an electric current to the secondary currents, the thermal relay, thermal relay through normally open or normally closed contacts, control the tripping coil, make the switch, instantaneous large current trip is to make use of magnetic effect under the switch end there is a electromagnetic coil structure, when there is a large current or short circuit current (larger than switch overload current lot of 0, suction increases immediate effect of the electromagnetic coil to drive the switch tripping device, through mechanical adjustment screw to adjust the switch of the instantaneous tripping current.
The thermal electromagnetic structure does not need external power supply, the anti-interference is strong. You may not use tripping coils.
Through the current transformer circuit, electronic, check the switch current, has current value to control the output, the output control tripping coil, switch trip, advantage is of high precision, easy to adjust, set numerical directly or use potentiometer to adjust.
The disadvantage is that you need to use the tripping coil, which requires the power supply. The problem of the electronic circuit is more difficult to deal with, and the anti-interference ability is almost impossible.