Limitations of Motor Protectors！

The main purpose of motor protection is to protect the motor from burning, and the function of the protector is very limited, which is obviously an impossible task.

In practice, can cause the motor burned for many reasons, can probably be divided into the following categories:

(1) various reasons caused by motor overload, excessive current.

(2) the voltage is too low or too high, phase imbalance or phase failure (including contactor fault caused by the lack of phase) caused by the current imbalance;

(3) refrigerant leakage or piping problems caused by the return air pressure is too low, the motor cooling is not enough;

(4) the winding insulation is damaged or the refrigerant water content is too high, the segment road burned, etc.

Theoretically, overload protection can effectively cope with the first 2 cases, while thermal protection can cope with the first 3 cases. The "short circuit" in the fourth case may be related to quality or installation, or to metal chips or high water content of refrigerant. In practice, several situations may occur at the same time. It is not possible to always test with a brand new compressor, as in the laboratory, and often the problem is simplistic.

The biggest limitation of the thermal and overload protection currently in use is that it is not possible to avoid all of the above phenomena at the root, and therefore the protection of the motor can only remain as a "cooling therapy" after the fact, both temporarily shutting down and allowing the compressor to cool down naturally before running. The thermal protection period and overload protection period is not limited by the number of suction and the motor will often burn up in the cycle of "protection - operation - protection - operation again". For unexpected events, such as winding insulation damage or short circuit caused by copper chips, the motor will burn up instantly at high temperature, and the thermal protector and overload protector are too late to react and protect. "Heat" and "overload" is the appearance of the motor burned rather than the root cause, and naturally can not rely on a thermal protector or overload protector alone to solve the problem, which is the motor burned still can not completely avoid the reason.