Current Tranformer Testing

Hi All

I don't know if this is the correct location on the forum but i'll ask anyway.

I would like to know if there are any devices on the market that can simulate a variable load up to 5A, equivalent to that given out from CT's. It is for testing ammeters and over current relays before the panels leave the workshop. Are there even any testing rigs we can set up from readily available components?

regards

Jonny

Multiple Vsd Failures

Hi guys, I just registered today as I have run out of options and can only hope there are smarter people out there than we have had in on this site. Basically below is the story and if you have time i'd appreciate you reading it and giving me some ideas no matter how trivial they may seem.

The company I work for got a contract to supply and fit the electrical control panel and wiring to motors etc of a waste recycling plant. We have done about 50 of these plants, maybe more, with the stipulation that we bear no responsibility for the electrical supply to our control panel, that lies with the customer. We have had no faults in the past.

This contract required a slightly larger panel than anything we have done before but not by much. It consists of a large PLC controlling about 30 motor starters and 10 variable speed drives (inverters). Plus a few other bits and pieces. Each VSD has its own input reactor (choke). The supply is from a 550kva generator, under full load our plant only draws around 120kva. (there is a terrible power factor of 0.6 so the apparent power used is only 80kw.)

Basically what is happening is that every day or so a vsd fails, always at the input side ie. the dc link is completely wiped out. We have tried different generators with varying degrees of success. With one generator we had no failures for 2 weeks but then the generator itself failed. We put a power analyser on the panel and see very little voltage fluctuation, about 5volts as the plant comes on and off load. We have measured harmonics with a result that we have 2.5% deviation on the voltage and 3% deviation on the current. Frequency could not be more stable at 49.9hz. Nothing else has failed on the plant except a 230vac/24vdc psu which failed this morning.

We tried changing the input chokes to output chokes to see if that would make any difference but we are still having failures. There has also been a power quality expert on site and he can find no fault with the supply and no fault with our installation. I know the supply has nothing to do with us but we have to help in finding a solution as we are replacing the vsd's until a conclusion has been found. Plus I have now been onsite for nearly 4 weeks incase there is a failure so that I can fix it as quick as possible. The thing is I am fixing the symptoms not the problem.

Can anybody offer any help or advice, we have completely run out of ideas and the company that bought this plant is losing money hand over fist as the downtime spent in solving different situations is crazy.

thanks

Jonny