Thread Starter: jayanta Started: 7/18/2010 10:03 PM Replies: 10
Dear All / Mr. Deep I like to inform you that the said 63A MCCB is Siemens make Characteristic „D“, & 80A MCCB is Characteristic „L“. I think (after watching MCCB catalogue) these two types of Characteristic MCCB is totally different. I also like to inform you that we tested the said transformer using lots 80A (same type) MCCB. So, please inform/guide me I/C MCCB selection calculation to avoid MCCB tripping at switching inrush. it would be better if anyone can give me supporting document also. For any information anyone can also mail me (firstname.lastname@example.org). Please guide me with supporting document. Jayanta
We have to see that an inrush current of 20...30 x In (rated current) is realistic.
Instantaneous trip (Ii) of a MCCB is about 10...13 x In. Therefore the circuit-breaker must be operated in its lower setting range.Example: Inrush current for a transformer In = 500A may be higher than 10000 A.Selection: Breaker In = 1000A, setting of In = 500 A, Ii = 11 x In = 11000 A (22 x setting of In).It must not be forgotten that the circuit breaker has to trip on the minimum short-circuit Ikmin. So the breaker should provide short time delayed short-circuit protection (Isd), which normally can be set to 2...10 x In and a time delay of a few hundred milliseconds.Please be aware not to use a breaker for motor protection. Phase-failure sensitivity may lead to unintentional tripping behaviour.