[RE-wrenches] Transformer inrush

[William Miller]

Dick:

Thanks for the reply.  To clarify, we have tried his with one transformer 
and with two transformers.  Our success rate is lower powering one 
transformer.  My hunch is that the capacitance of the feeder is buffering...

I wonder if I use a large solid state relay with zero crossing switching I 
might have better luck.


William Miller


At 06:23 PM 5/12/2010, Richard L Ratico wrote:
>Bill,
>Your branch circuit breaker is pretty small.
>Are you energizing both transformers simultaneously? If so, it might help to
>energize them individually.
>
>The branch breaker can be up to 250% of the step up transformer's primary
>rating. 10kVA/240V=41A.
>41A x 2.5=100A. (round numbers). To do this you would also need overcurrent
>protection on the transformer secondary.
>
>Of course, you've already got the 100A main tripping. That's why I asked if
>you're
>energizing them simultaneously.
>
>Transformer inrush can be a real problem.
>
>Hope this helps.
>
>Dick Ratico
>Solarwind Electric
>
>--- You wrote:
>Friends:
>
>I have on off-grid client that is trying to eliminate winter generator run
>time.  He has a rental on another corner of the property that has grid
>power.  When it was installed, he put in an extra meter, hoping to use it
>to run a utility back up feeder to charge batteries.
>
>We are now installing this feeder.  We purchased two 10KVA 240/600 volt
>transformers to bump the voltage to 600 and then back down to 120/240.
>
>Here's the problem:  when we energize the circuit breaker that feeds the
>transformer, the circuit breaker AND the main breaker trip.  The
>transformer is 10KVA, the main is 100 amps and the branch breaker is
>60A.  The breakers hold sometimes but trip other times.  This is obviously
>an inrush problem.  How do I correct this problem?
>
>Thanks in advance,
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