【Daily Question 20101109】During the power-up of a transformer, the inrush current is very large; why doesn’t the differential protection activate?
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This post was last edited by zyz8438 on 2010-11-13 12:40. [Question] When a transformer is powered on, it experiences a large inrush current; this current can reach 5–8 times the rated current. Moreover, this current exists only on the power supply side and not on the load side; in other words, a large differential current occurs when the transformer supplies power. Then why doesn’t the differential protection of the transformer activate? 【Answer】 When a transformer is powered on, there is a large inrush current on the power supply side. This inrush current has a very distinct characteristic: its harmonic components are relatively large, especially the second harmonic. Therefore, in transformer differential protection, the concept of second-harmonic braking is employed. Although the differential current is very large at the moment of closing, and its second harmonic component is also high, the differential protection still does not operate!
Remove the differential protection switch before powering on
Just remove the differential protection switch before powering on; I agree with what was said above
What the two people upstairs said is incorrect; it is not allowed to remove the protection switch when supplying power to the transformer! What if there is a short circuit in the transformer, and the protection switch is removed before power is supplied, causing the protection to fail to function? Who would dare to take responsibility for that?
Continue answering: Increase the differential protection setting threshold appropriately, and restore the setting once the excitation inrush current has subsided
When a transformer is powered on, there is a large inrush current on the power supply side. This inrush current has a very distinct characteristic: its harmonic components are relatively large, especially the second harmonic. Therefore, in transformer differential protection, the concept of second-harmonic braking is employed. Although the differential current is very large at the moment of closing, and its second harmonic component is also high, the differential protection still does not operate!