The kinds of automatic control in the circuit protection link and function

In the automatic control circuit has the following protection link, is also a general automatic control circuit of the protection of the link. ( 1) Short circuit protection of motors, electrical appliances and wire insulation damage or failure occurs, can cause a short circuit accident. Great cause overheating and short-circuit current electric power may cause electrical equipment damage, even cause fire as a result, so the requirements in the event of a short circuit fault, control circuit should be able to quickly cut off the circuit. Short circuit protection of commonly used method is to use a fuse or circuit breaker. The protection device should not be influenced by the starting current and false action. So according to the requirements of fuse, the choice of circuit breaker and setting. ( 2) Long-term overload protection and long-term overload operation, open phase protection motor winding temperature rise would exceed its value, cause insulation material brittle, shorten the life, serious when still can make motor damage. Overload current is larger, to allow temperature rise for the shorter the time. The commonly used thermal relay is the long-term overload protection device. Thermal relay can't double as short circuit protection, because of the short circuit occurs, it may be also too late action has cause damage to electrical equipment. According to statistics, burn out motor by open phase running the Numbers, in some units have more than 80% of the total number of damage to the motor, so the motor should be open phase protection link, that is to say, want to choose the thermal relay with open phase protection function. ( 3) Zero voltage and low voltage protection power supply voltage for some reason suddenly disappeared, the motor will be shut down. Once the voltage returns to normal, if the motor starting on their own, often can cause equipment damage or personal injury, will be caused by many devices at the same time starting too much impact on power supply network. Therefore, in the power grid voltage disappears, should immediately cut off power supply, realize zero voltage protection. Power supply voltage lower too much, can cause motor speed down or even halt; Under the condition of invariable load torque, motor current increases, winding overheating and damage; Voltage is too low will cause some electric release, control disorders. When the power supply voltage drops below allowable values, therefore, need to cut off the power and low voltage protection. The bartender blackout road itself has the function of protection and under-voltage protection pressure loss. When the power loss of pressure or serious undervoltage, contactor armature to release, motor to stop running. When the voltage returns to normal, contactor coil and electricity themselves, only if the operator once again press the start button, the motor will start. Some circuit requires better zero pressure and under-voltage protection, also adopts special undervoltage relay or under voltage protection circuit.