The specific situation is: the installed motor differential protection, the current measured by current transformers at both ends of the motor is about 1.9 amperes, and the differential current should be 0 or a very small value.However, the differential current displayed by the device is about 3.4 amperes. Note: The circuit is OK, ABC three-phase phase continuity is OK, the motor differential protection device is OK, and the motor is running normally. I would like to ask Darren what causes this situation. I took the device back to the company for testing, but there is no differential current. Moreover, the device can only measure the second harmonic at most, and the differential current calculation is not related to harmonics.The transformer is also from the same manufacturer and batch. Now the differential current is abnormal.Tell me what you know!Help!
This is a specific example of polarity reversal. If the CT polarity on both sides is the same, the polarity of the access protection device should be the same.The differential protection can be put into operation only after the polarity is checked to be normal. The polarity can be checked through the on-site detection of the phase sequence meter. The current of each phase on both sides of the motor should be one in and one out, and the difference value is zero. The device has indications.
