Working principle of compressor overheating protection and Breaker protector switch
The circuit consists of a heating wire, a bimetal sheet and two static contacts, which are connected in series in the compressor circuit. When the current in the circuit is too large, the heating wire is heated and the dish-shaped bimetal is baked. When the bimetal heats up, it will arch in the opposite direction, thereby breaking the contacts; When the temperature of the compressor casing or the motor is too high, even if the working current is normal and the heating wire generates little heat, the bimetal will deform and bend upward, detaching from the two static contacts and cutting off the circuit. This protector can be reset automatically and has the double protection function of over current and over temperature rise.
According to different installation methods, it can be divided into two types: external and internal:
(1) External protector:
It is installed on the sealed terminal of the compressor casing and closes to the cover to sense the temperature of the compressor casing. Because there is a process of conduction and convection from the heating of the motor to the heating of the casing, and another process from the heating of the casing to the action of the protector, the accuracy and reliability of this protection method are relatively poor. But because of its simple manufacture, the same bimetal can be used to make different protectors by adjusting the screw height. In addition, it is convenient to install and maintain, and has low cost, so it is generally applied to low-power domestic air-conditioning compressors.
(2) Built-in protector:
Divided into tying and plug-in type, tying is to tie the protector with the motor coil, directly sense the temperature change of the coil, the response is fast and accurate; The plug-in type is to connect the protector to the sealed terminal, and use the heat conduction of the refrigerant to sense the abnormal temperature of the motor. The protection is more accurate when the refrigerant does not leak. However, once the refrigerant leaks, the protection performance is poor.
In short, the built-in protector is more sensitive, more accurate, more reliable, and more applicable to the motor temperature sensing than the external type (the general air conditioner compressor can be used).
However, because it is installed inside the compressor, it is required to be small in size and able to adapt to harsh environments such as high temperature and high pressure changes inside the compressor. It has high requirements on its design and manufacturing, and the cost is several times more expensive than the external type.
1) Different compressor overload protectors have different protection effects on the compressor. The built-in protector is more sensitive than the external protector and has a greater protection effect on the compressor.
2) When the refrigerant is insufficient, the protection of the compressor by the built-in protector or the external protector is very limited, so the protection against the lack of refrigerant should be added in the air conditioning system.
4) The overload protector cannot protect under high compression ratio. Low pressure protection measures must be provided to protect the compressor.
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