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Electrician knowledge sharing how intelligent motor protector work

Click volume: 584 Release time: 2022-12-20

Intelligent motor protector is composed of a three-phase current transformer, detection, amplification, delay, adjustment circuit, and executive relay. When the detection circuit detects that the current of the current transformer is out of phase or greater than the set value, it will be amplified by the amplifier. Make the relay operate, and the relay contacts are connected in series in the AC contactor coil power supply circuit. After the relay operates, the AC contactor will be powered off to protect the motor. The delay circuit is used to avoid the starting current of the motor, and the adjustment circuit is used to The operating current of the protected motor precisely set to operate the current.

NDD3B(JD-5B) Motor protector

In short, the intelligent motor protector detects the current signal in the circuit through the internal current transformer, and the protection circuit analyzes the current signal to determine whether it is overcurrent, three-phase imbalance, or phase loss, to achieve the purpose of protection, the principle is that the circuit will be cut off if the zero-sequence transformer is unbalanced, and the connected AC contactor will be disconnected to protect the motor.

Smart Motor Protector Features
(1) Protection function.
The protection function of the motor synthesizer is very strong, effectively integrating overload protection, overcurrent protection, stall protection, underload protection, phase loss/unbalance protection, grounding protection, startup acceleration overtime protection, external fault protection, under-voltage protection, leakage current Protection and under-power protection and other protection functions.

(2) Control mode.
The control mode can be flexibly selected according to actual needs, including direct, reversible, two-speed, auto-coupling step-down, star/delta, resistance step-down, and other modes.

(3) Communication function.
Most of the integrated protectors are compatible with Modbus-RTU, Profibus-DP, or DeviceNet communication protocols.

(4) Measurement function.
It can realize the sampling measurement of many important parameters, such as three-phase current, heat capacity, ground current, current unbalance rate, leakage current, three-phase voltage, active power, etc.

Protection principle of the intelligent motor protector
(1) Differential protection
When a fault occurs inside the motor and the differential current increases beyond the differential protection setting value, the output node 01 of the protector will be automatically closed, the KM intermediate relay and the opening circuit will be energized, and finally, the motor will stop and will not run.

(2) Ground protection
When the motor has a ground fault, the output node 0102 of the protector is automatically closed, and then KM and the opening circuit are energized, and the motor stops and does not run.

(3) Low voltage protection
If the grid voltage is reduced to only 50% of the rated voltage, after 600ms, the output node 0101 of the protector will be automatically closed, the KM will be energized, the opening circuit will be energized, and the motor will stop running.

(4) Overcurrent protection
If the motor current exceeds the over-current protection setting value, the output node 04 of the protector will be closed automatically, the KM will be powered, the opening circuit will be powered, and the motor will stop running.

Points for attention in the use of intelligent motor protectors
(1) When debugging the current regulation, it needs to be carried out within the standard voltage of 380±1%.
(2) The performance of the protector should be checked regularly, and various tests such as the overload test and phase failure test should be carried out at the same time.
(3) Due to the influence of the internal structure of the intelligent motor protector itself, the overcurrent adjustment scale cannot show a linear ratio. At this time, the actual debugging needs to be used as a standard.
(4) Once the failure of the motor to stop occurs during the specific operation process, in this case, the staff first needs to check whether the motor has an abnormal temperature;
If the motor has a high temperature, it is likely to stop due to overload;
If there is no excessive temperature, at this time the staff can judge that it is likely to be a tripping fault caused by the open phase of the line. In this case, the staff needs to check whether the three-phase power supply is normal, and at the same time check Whether there is any bad contact on the AC contactor and whether there is any looseness on the three power lines of the motor.
If all the above are normal, you need to press and hold the start button at this time and observe whether the indicator light on the protector panel is normal. Generally, the indicator light will go out when the phase is broken or overloaded. At this time, if the indicator light is normal, release the start button. If the indicator light is abnormal, you need to stop the intelligent motor protector immediately. And carefully check the self-locking contacts of the AC contactor. If it is confirmed that all the faults have been eliminated, the motor can be started at this time to make it continue to run, thereby effectively avoiding various faults.

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