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#181422 - 10/07/08 12:36 PM 75KVA Auto Transformer  
mr_electrician  Offline
Member
Joined: Jun 2007
Posts: 106
London, Ontario
I have been asked to temporarly hook up a piece of equipment. It is 480V 3 phase and has 90A fuses on its main disconnect. The majority of the load is the electric heaters. I have a 75 KVA auto transformer (600/480) that I am going to use. We have a 600V service. I was wondering if anyone has had any issues trying to power up a 75KVA transformer with 60A primary fuses on it. I want to disconnect the electric heaters on the piece of equipment for now since we are onlyy worried about testing the other connected loads such as motors and I/O. This would leave a very small connected load but I am worried that the inrush of the transformer would blow the 60 amp fuses. Should I be safe and fuse it at 80 amps as if it were fully loaded?


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#181448 - 10/08/08 12:49 PM Re: 75KVA Auto Transformer [Re: mr_electrician]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
I have an installation here that powers a 75 KVA transformer with 60A Time delay fuses The run to the transformer is long, more than 100 meters. 60 Amp fuses were chosen because the secondary powers a 200 amp panel and there is no secondary OC protection so 60 A was the biggest fuse that could match without another OC device on the secondary or a 225 amp panel. They have been operating for about 2 1/2 years without an inrush failure on these fuses. I do think the impedance of the run helps too


#181449 - 10/08/08 12:50 PM Re: 75KVA Auto Transformer [Re: mr_electrician]  
mr_electrician  Offline
Member
Joined: Jun 2007
Posts: 106
London, Ontario
So those who are interested know, I went ahead and strangled the 75KVA transformer primary to 60A and it held when I turned it on. So I guess now I can go ahead and start seeing what does and doesn't work on this boat anchor. Did I mention that it has sat for 2-3 years with no power to it. Allready I have to reload the plc program. Battery went dead!!


Never trust an electrician with no eyebrows!!


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