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Motor protection protection principle and function
- Mar 22, 2018 -

● Overload protection ● Underload protection ● Stall protection ● Blocking protection ● Overheat protection

● Phase sequence protection ● Undervoltage protection ● Overvoltage protection ● Underpower protection ● Start overtime protection

● Phase failure protection ● Unbalance protection ● Ground protection ● Leakage protection ● External fault protection

Overload protection

When the motor is under overload fault, if it exceeds its rated current for a long time, it will cause the motor to overheat and the insulation will be reduced and burned. The protector calculates the thermal capacity of the motor according to the heating characteristics of the motor and simulates the motor heating characteristics to protect the motor. Protection of the characteristics of different trip levels

Underload protection

When the motor is loaded with a pump type load, the motor will produce no-load or under-load operation. The protector provides under-load protection. When the percentage of the three-phase average current and rated current is lower than the set value, the protector shall In the action (delay) set time or within the alarm time alarm.

Locked/blocked protection

When the motor is starting or during operation, if the electric timing shaft is jammed due to excessive load or mechanical reasons, failure to remove the fault in time will cause the motor to overheat, reduce the insulation and burn the motor, and the stall protection applies to the motor. Start this type of fault to protect it. The blocking protection is used to protect the motor during operation. When the current reaches the set current, the protector should act or alarm during the action (delay) for a set time. Alarm within the time.

Phase loss (unbalanced) protection

The motor in phase failure (unbalanced) fault is very dangerous. When the motor is broken or the three-phase current is seriously unbalanced, if the unbalance rate reaches the protection setting value, the protector is protected according to the set requirements and issued. Stop or alarm instructions to make the motor safer.

Ground/earth leakage protection

The protector also has ground protection and leakage protection. The grounding protection current signal is taken from the vector sum of the internal current transformers, which is used to protect the short circuit protection of the phase wire of the motor metal housing. The protector can detect the fault current of 30mA~50mA by adding the leakage transformer and it is mainly used for indirect Grounded

Protection to ensure personal safety.

External fault protection

When the protector detects the presence of an external fault, the external fault digital input and the digital input defined by the protector are inconsistent. The protector is protected according to the set requirements to ensure the safety of the motor equipment.

Start overtime protection

In the process of motor starting, the protector only has phase protection (unbalance), ground/leakage and other protection functions, and the rest of the protection functions do not work. After the start, all protection functions (according to user settings) are automatically input when When the motor starting time exceeds the user-defined starting time and the current is still greater than 1.1 times the rated current, the protector is protected according to the set requirements. A stop command is issued within the set time of the action (delay) to stop the motor operation.

Phase sequence protection

A protector with a phase sequence protection function should not operate when the voltage phase sequence on the power supply side matches the set sequence. When the protector detects that the phase sequence of the motor d is wrong, the motor should not start.

Undervoltage protection

If the voltage is too low, it will cause the motor speed to decrease or even stop running. When the motor running voltage drops to the set under-voltage protection range, the protector will be protected according to the set requirements, and it will act within the time set by the action (delay) or Alarms during the alarm time to avoid confusion caused by important production processes and seriously affect production.

Overvoltage protection

If the voltage is too high, it will cause damage to the insulation of the motor. When the motor operating voltage exceeds the set protection voltage, the protector will be protected according to the set requirements, and it will act within the set time (delay) or alarm during the alarm time. Ensure the safety of the motor equipment.

Underpower protection

The motor loses the mechanical output capacity due to the damage of the transmission device. Under the underload operation, the motor power factor is low, but the motor current is large, and the reactive power of the system is consumed greatly. When the percentage of load power and rated power is lower than the set action value The protector operates within the set time of the action (delay) or alarm within the alarm time.

Overheat protection

Overheat protection uses mathematical methods to establish the heating model of the motor and solves the problem of thermal protection of the low voltage motor in principle.

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