50 kva transformer problem
50 kva transformer problem
(OP)
Hello, Help We just installed a 50kva transformer going from 480 to 120/240 with a 100A breaker and when you throw the breaker we get a flash from the transformer. After speaking to manufactuer it is wired correctly and they said we needed a 225A breaker .We are getting the flash on the primary side, we do not see any evidence of anything burned.They claim it is end rush. On the secondary side is only a 200A panel. Thank You Rickie






RE: 50 kva transformer problem
Chances are that one or more of the connections is loose.
Probably, the electrician put the cable in the connector and tightened it. Not good.
The proper procedure is to;
1> Twist the cable back and forth in the connector after tightening and re-tighten. Repeat until it is not possible to tighten the connector any more.
2> Use channel-lock type pliers to take the twist out of the cable strands before inserting into the connector. Check by twisting the cable and retightening.
The cable strands take less space in the connector when they are straight than when they have the original twist. If the cable is inserted into the connector and just tightened once, the strands will tend to untwist and become very loose if the cable is disturbed, such as when installing the next cable. Twisting the cable encourages the strands to straighten out. You will be surprised at how loose a connection will become when the cable is first twisted.
Method "1" works best for larger cables which have different layers of strands twisted in opposite directions.
I have surprised many electricians over the years by giving their connections a little twist and dropping the cable out of the connector. I have invited electricians to tighten a cable connection as much as possible and then given the cable a twist and dropped it out of the connector.
respectfully
RE: 50 kva transformer problem
RE: 50 kva transformer problem
RE: 50 kva transformer problem
Check configuration connections (delta-delta, delta-Y, etc)
Also, for breaker sizing, check NEC Art. 450, Table 450.3(b)
regards
RE: 50 kva transformer problem
RE: 50 kva transformer problem
RE: 50 kva transformer problem
RE: 50 kva transformer problem
RE: 50 kva transformer problem
RE: 50 kva transformer problem
The inrush effect means you have a very high instantaneous current at energization, so V=IR across the high-resistance joint is giving you a little spark around it.
De-energize and measure the series resistance of each segment of the power delivery chain. Preferably with a "ductor" (DLRO) using at least ten amps through current.
Check for loose connections and possible spark gaps at or between the tap arrangement.
Pull the cover off, put a video camera on a tripod, start the camera, turn off the lights, and energize the transformer.
Double-check your ground conductor integrity and verify high-to-low insulation integrity before putting it in service.
RE: 50 kva transformer problem
RE: 50 kva transformer problem