15 essential protection principles for electric motors

Hengli Motor on several motor protection principles and functions

1. Overload protection: When the motor operates beyond its rated current for a long time under overload fault, it will cause the motor to overheat, reduce insulation and burn out. The protector calculates the thermal capacity of the motor based on its heating characteristics, simulates the heating characteristics of the motor to protect the motor, and provides overload protection based on the characteristics corresponding to different trip levels.

2. Underload protection: When the load carried by the motor is a pump type load, no-load or underload operation of the motor will cause harm. The protector provides underload protection. When the percentage of the average current of the three phases to the rated current is lower than the set value, the protector should act within the set action (delay) time or alarm within the alarm time.

3. Blocked rotor protection: During the start-up or operation of the Hengli motor, if the electric timing shaft is stuck due to excessive load or mechanical reasons, and the fault is not resolved in time, it will cause the motor to overheat, reduce insulation, and burn out the motor. Blocked rotor protection is suitable for protecting against such faults during the start-up of the motor. Blocked rotor protection is suitable for protecting against such faults during the operation of the motor. When the current reaches the set action current, the protector should act within the set action (delay) time or alarm within the alarm time.

4. Phase failure (unbalance) protection: When the motor is in operation due to a phase failure (unbalance) fault, the harm to the motor is significant. When the motor experiences a phase failure or severe three-phase current imbalance, if the unbalance rate reaches the protection set value, the protector will protect it according to the set requirements, issue a stop or alarm command, and make the operation of the motor safer.

5. Grounding/leakage protection: Hengli motor protector has both grounding protection and leakage protection functions. The grounding protection current signal is taken from the vector sum of the internal current transformers, and is used to protect the short circuit protection of the phase line to the metal shell of the motor. The protector can detect fault currents of 30mA~50mA by adding a leakage transformer, mainly used for non direct grounding protection to ensure personal safety.

6. External fault protection: When the protector detects an external fault and the external fault switch input is inconsistent with the switch input state defined by the protector, the protector protects the motor equipment according to the set requirements to ensure safety.

7. Starting timeout protection: During the starting process of the Hengli motor, the protector only has protection functions such as phase failure (imbalance), grounding/leakage, etc., and other protection functions do not work. After the starting is completed, all protection functions (set by the user) are automatically activated. When the starting time of the motor exceeds the user's set starting time and the current is still greater than 1.1 times the rated current, the protector protects according to the set requirements and issues a stop command within the set action (delay) time to stop the motor operation.

8. Phase sequence protection: A protector with phase sequence protection function. When the voltage phase sequence on the power supply side of a constant force motor is consistent with the set sequence, the protector should not operate. When the protector detects that the phase sequence of electric motor D is connected incorrectly, the motor should not be able to start.

9. Undervoltage protection: Low voltage can cause the motor speed to decrease or even stop running. When the operating voltage of the motor drops to the set undervoltage protection range, the protector will protect according to the set requirements, and will act within the set action (delay) time or alarm within the alarm time to avoid confusion caused by important production processes and seriously affect production.

10. Overvoltage protection: Excessive voltage can cause damage to the insulation level of the motor. When the operating voltage of the motor exceeds the set protection voltage, the protector will protect it according to the set requirements. It will act within the set action (delay) time or alarm within the alarm time to ensure the safety of the motor equipment

11. Under power protection: Due to damage to the transmission device, the motor loses its mechanical output capability and operates under underload. The power factor of the motor is low, but the motor current is high, consuming a large amount of reactive power from the system. When the percentage of load power to rated power is lower than the set action value, the protector will act within the set action (delay) time or alarm within the alarm time.

12. Overheating protection: Overheating protection uses mathematical methods to establish a heating model for electric motors, which theoretically solves the thermal protection problem of low-voltage motors.