Motor protection protection principle and function
â—Overload protection â—Underload protection â—Lock protection â—Block protection â—Overheat protection â—Phase sequence protection â—Under voltage protection â—Overvoltage protection â—Under power protection â—Start time protection
â—Failure protection â—Unbalance protection â—Ground protection â—Leakage protection â—External fault protection
Overload protection
When the motor exceeds its rated current for a long time under the overload fault, the motor will overheat, the insulation will be reduced and burned. The protector calculates the heat capacity of the motor according to the heating characteristics of the motor, and simulates the heating characteristics of the motor to protect the motor. Protect features corresponding to different trip levels
Underload protection
When the load on the motor is a pump load, the motor will be harmed by no-load or under-load operation. The protector provides under-load protection. When the average current and rated current of the three-phase are lower than the set value, the protector should be Action during the action (delay) set time or alarm during the alarm time.
Stall/blocking protection
When the motor is started or during operation, if the electric motor shaft is stuck due to excessive load or mechanical reasons, the motor will be overheated, the insulation will be reduced and the motor will be burned, and the stall protection will be applied to the motor. This kind of fault occurs when starting to protect. The blocking protection is suitable for protection when such fault occurs during motor operation. When the current reaches the set current, the protector should act or alarm during the set time of action (delay). Alarm during the time.
Phase failure (unbalanced) protection
In the case of phase failure (unbalanced) fault, the motor is very harmful. When the motor is out of phase or the three-phase current is seriously unbalanced, if the unbalance rate reaches the protection set value, the protector is protected according to the set requirements. Parking or alarm commands make the operation of the motor safer.
Ground/leakage protection
The protector has both grounding and leakage protection. The grounding protection current signal is taken from the vector sum of the internal current transformer to protect the phase line from the short circuit protection of the metal casing of the motor. The protector can detect the fault current of 30mA~50mA by adding the leakage transformer, mainly used for indirect Grounding protection to ensure personal safety.
External fault protection
When the protector detects that an external fault has occurred and the external fault switch input is inconsistent with the switch input state defined by the protector, the protector is protected according to the set requirements to ensure the safety of the motor device.
Start timeout protection
During the starting process of the motor, the protector only has the functions of phase failure (unbalance), grounding/leakage, etc. The other protection functions do not work. After the start, all protection functions (set by the user) are automatically input. When the motor starting time exceeds the starting time set by the user and the current is greater than 1.1 times of the rated current, the protector is protected according to the set requirements, and the parking command is issued within the set time of the action (delay) to stop the motor running.
Phase sequence protection
A protector with phase sequence protection shall not operate when the voltage phase sequence on the power supply side matches the set order. When the protector detects that the phase sequence of the electric d is wrong, the motor should not start.
Undervoltage protection
If the voltage is too low, the motor speed will decrease or even stop running. When the motor running voltage drops to the set under-voltage protection range, the protector is protected according to the set requirements and operates within the set time of the action (delay). 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, the degree of insulation of the motor will be damaged. When the running voltage of the motor exceeds the set protection voltage, the protector will be protected according to the set requirements, and it will operate within the set time of the action (delay) or alarm during the alarm time. Ensure the safety of the motor equipment.
Underpower protection
The motor loses mechanical output due to damage of the transmission device. When the underload is running, the motor power factor is low, but the motor current is very large, and the system is largely deactivated. 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 alarms during the alarm time.
Overheating protection
The overheat protection uses mathematical methods to establish the heating model of the motor, which solves the thermal protection problem of the low voltage motor in principle.
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