How does a motor protector work, what is the working principle of a motor thermal protector?

The function of the motor protector is to give the motor a comprehensive protection control, in the motor overcurrent, undercurrent, phase failure, stalled, short circuit, overvoltage, undervoltage, leakage, three-phase unbalance, overheating, grounding, bearing wear, stator and rotor eccentricity, winding aging to alarm or protection control.

Due to many reasons such as voltage instability, phase failure and overcurrent, the motor is damaged, resulting in abnormal operation, and the motor must be protected, so there is a motor protector.

There are many varieties of protectors, such as phase breaking, over-current and under-current protection, time protection, temperature protection, leakage protection, overheating protection, and many other protectors, and the protectors are divided into mechanical protection and electronic protectors, etc., the principle is to protect the motor in various conditions above, so that the loss is minimized and even to protect the safety of human life.

The motor protector consists of a three-phase current transformer.

Detect, amplify, delay, adjust circuits, and perform relay composition. When the detection circuit detects that the current induced by the current transformer is out of phase or greater than the set value, it is amplified by the amplifier to make the relay operate.

The relay contacts are connected in series to the contactor.

In the coil power supply circuit, the contactor is de-energized after the relay is acted, which plays a role in protecting the motor. The delay circuit is used to avoid the motor starting current, and its duration is adjustable. The adjustment circuit is used to accurately set the operating current according to the working current of the protected motor.

If the current is too high, it will trip.

The motor protector is suitable for AC 50Hz, rated working voltage ACC380V and below in the power supply circuit and AC contactor and other switching appliances to form a motor control circuit. When the main circuit of the motor is out of phase, overload, stalled, three-phase unbalanced, overvoltage, undervoltage, short circuit, grounding and other abnormal working conditions, disconnect the three-phase power supply of the switchgear contact and the segmented motor in time to protect the motor quickly and reliably. If you want to know more, I have the information here, and I will send you a copy.

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From the structure and working principle of the thermal relay, it can be seen that it works by using the thermal effect of electric current. When the current flowing in the heating element connected to the main circuit exceeds the allowable value and after a certain period of time (thermal inertia), the bimetal sheet with different linear expansion coefficients is decoupled by the fiber barrier and high thermal bending deformation, so that its normally closed contact (connected in series in the control circuit) is disconnected, the contactor coil is de-energized, and the main circuit of the motor is disconnected, so as to achieve overload protection. Because the thermal relay has thermal inertia, it will not act when the motor is started or overloaded in a short time, which can avoid the necessary shutdown of the motor.

When a short-circuit fault occurs in the motor, the short-circuit current reaches a large value in a very short period of time, and the power supply needs to be cut off quickly to protect the motor. However, the heat accumulation of the heat element in such a short period of time is not enough to deform the bimetal sheet to drive the contact action. Therefore, the thermal relay cannot meet the requirements of instantaneous power failure when the circuit is short-circuited, so it cannot be used for short-circuit protection.

The working principle of the thermal relay is to generate heat by the current flowing into the heating element, so that the bimetal sheet with different expansion coefficients is deformed, when the deformation reaches a certain distance, the connecting rod action is promoted, the control circuit is disconnected, so that the contactor loses power, the main circuit is disconnected, and the overload protection of the motor is realized. As an overload protection component of the motor, the relay has been widely used in production due to its small size, simple structure and low cost.

The motor protector is a kind of equipment used to protect the motor with the guard, it can monitor the current, temperature, voltage and other parameters of the motor chain oak, when these parameters exceed the set safety range, the protector will automatically cut off the power supply to avoid damage or danger to the motor. Motor protectors are usually used for motor protection in industrial production, which can improve the reliability and safety of electric motors.

Summary. The principle of single-phase motor start protector can be divided into the following four aspects:

The principle of single-phase motor start protector can be divided into the following four aspects:

1. When the starting load of the single-phase motor is large, the single-phase motor will cause low-voltage jitter, which will produce electromagnetic explosion and no-load protection to protect the motor from destruction; 2. Because the instantaneous current will increase greatly after the single-phase motor starts, if the instantaneous current exceeds the rated current of the motor, the motor will be damaged, so it has the effect of starting overcurrent protection; 3. During the operation of the single-phase motor, if the load is abandoned, it is necessary to open the switch clockwise to interrupt the energy** to ensure that the motor is shut down quickly and safely, so as to avoid damage to the motor; 4. During the operation of the single-phase motor, if the truck occurs, the no-load torque current will be greatly increased, and the single-phase motor will be overloaded, and the overload protector will play a role to prolong the service life of the equipment and prevent the equipment from malfunctioning.