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    EN
    ZH
    Dazhong Electric Motor
    Industry News
    Fifteen protection principles for large and medium-sized electric motors
    Release Time:2023-04-10

    overload protection


    When the motor operates for a long time beyond its rated current under overload fault, it will cause overheating, insulation reduction, and burning. The protector calculates the motor's thermal capacity based on the motor's heating characteristics, simulates the motor's heating characteristics, and protects the motor against overload protection based on the corresponding characteristics of different tripping levels.


    Underload protection


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


    Locked rotor/blocked protection


    If the electric motor gets stuck during startup or operation due to excessive load or mechanical reasons, and the fault is not resolved in a timely manner, it will cause the motor to overheat, reduce insulation, and burn the motor. Locked rotor protection is suitable for protecting the motor from such faults during startup, and blocking protection is suitable for protecting the motor from such faults during operation. When the current reaches the set action current, The protector should act within the set time of action (delay) or alarm within the alarm time.


    Phase loss (imbalance) protection


    The harm of the motor during phase failure (imbalance) operation is significant. When the motor experiences phase failure or severe three-phase current imbalance, and the imbalance rate reaches the protection setting value, the protector will protect according to the set requirements and issue a stop or alarm command to make the operation of the motor safer.


    Grounding/leakage protection


    The protector has both grounding protection and leakage protection functions. The grounding protection current signal is taken from the vector sum of the internal current transformer, used to protect the short circuit protection of the phase line to the metal casing of the motor. The protector can detect a fault current of 30mA~50mA by adding a leakage transformer, mainly used for indirect grounding protection to ensure personal safety.


    External fault protection


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


    Start timeout protection


    During the starting process of the motor, the protector only has protection functions such as phase failure (imbalance), grounding/leakage, etc. The other protection functions are not effective. After the start is completed, all protection functions (set by the user) are automatically put into operation. When the starting time of the motor exceeds the user set starting time and the current is 1.1 times the rated current, the protector protects according to the set requirements and sends a stop command within the action (delay) set time, Stop the motor operation.


    Phase sequence protection


    A protector with phase sequence protection function should not operate when the voltage phase sequence on the power side is consistent with the set sequence. When the protector detects that the phase sequence of the electric motor d is connected incorrectly, the motor should not be able to start.


    Undervoltage protection


    If the voltage is too low, it 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. It will act within the set time of action (delay) or alarm within the alarm time to avoid important production processes from causing chaos and seriously affecting production.


    Overvoltage protection


    Excessive voltage can cause damage to the insulation 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 time of action (delay) or alarm within the alarm time to ensure the safety of the motor equipment.


    Underpower protection


    Due to damage to the transmission device, the motor loses its mechanical output capacity. During underload operation, the power factor of the motor is low, but the motor current is large, consuming a large amount of reactive power in the system. When the percentage of load power and rated power is lower than the set action value, the protector acts within the action (delay) set time or alarms within the alarm time.


    Overheat protection


    The overheating protection adopts mathematical methods to establish a heating model of the motor, which theoretically solves the thermal protection problem of low-voltage motors.


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