isolation transformer how to pick


Postby ericmark » Tue Dec 16, 2008 7:31 pm

I want to supply a complete domestic installation through an isolation transformer and not have any imported earth. The main supply is from a 16 amp socket which means 3.68Kva is the maximum but transformers are only available as 3Kva or 4Kva first thought is get a 4Kva but a little worried about in-rush. Not a clue as to type of MCB feeding the 16 amp socket and this could change anyway according to which marina the boat is moored in. I know from past experience that some transformers have more in-rush than others. I have read my book on Electrical circuit theory and technology which explains iron losses, copper losses with hysteresis and eddy current losses all interesting but does not really answer my question.
What to I look for to work out if it will have high in-rush and what do I look for to see what Ze will be and hence max boat side MCB’s that can be used. I know once fitted I will find out but a bit late then. If one transformer needs a soft start, but another can go direct on line. Then cost of soft start needs adding on.
Is there a simple soft start like powering through a resistor then after so many seconds shorting out the resistor?
Also I know again from experience with 110v transformers some use very little power on no load and others use quite a lot mainly those in portable yellow boxes cost much more to run than those designed to be fitted on a wall and permanently wired in.
Will I need to add power factor correction or should that be done by manufacturer like on florescent lights?
In the past
one I was not paying for power, and
two I could stipulate a D type MCB
but this time I can’t afford to make mistakes can anyone advise what to look for.
On a barge with concrete ballast weight is not a problem.
Eric
ericmark

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