240-440V transformer

Hi all,
Today I started to build my rotary phase converter, I have to spin it up with a drill but it does generate the other two legs once up and running. When some start caps are in stock I will buy some and use a momentary switch to run it without the drill. Anyway, it’s a 10HP idler, and I’m uk based so it’s being fed a live and neutral. The output of the idler is 240-215-215v, I’ll balance this at a later date. As my machines are 415-440v I bought an 8kva three phase transformer, which steps up the three phase output from the idler from 240v to 440v. When I put the transformer in the 240v three phase output of the converter, the 32amp MCB trips. The transformer must suck up too much current when power flows into it. How do I stand using the transformer as a single phase one, and powering the idler with just the single phase at 440v. I’ve seen others do it this way, but not with a three phase transformer. The transformer has three inputs and a neutral on the one side, and three outputs and a neutral on the other. Would I just connect the 240v live in L1 and the neutral in the neutral terminal, and take it out the other side, or is there more to it than that being a three phase transformer.
Thanks

Good Day

I have the same problem when connecting my transformer it trips my power so I'm stuck at the same place.

Regards

My 10 HP phase perfect requires 70 amp breaker and wire size to suit - and it has no idler motor load and no external transformer load

It would appear your MCB breaker is about half enough, and who knows how your wiring size matches up to that

What John Oder said.... you might need a soft-start on that.

I'd keep using it 3 phase.

Are you switching the transformer into the circuit after the converter is running? That is the right way t do it. Having it connected to the converter when converter is started will draw a lot of current and not work.

You are PROBABLY .. going to need to do two things. Three, maybe:

A) implement a more permanent version of "pony start", just as you are now doing with the drill motor. Start caps to kick a ten HP idler into action - no small chore, regardless - are not easy on the incoming line nor its protective devices.

I'd actually want to adapt an IC engine starter motor, run off a battery, so ZERO load was robbed at launch-time, and ALL available power was left for the RPC proper.. at least during that crucial "time window". Re-charge isn't hard.

B) Place a "soft start" between the RPC idler and the transformer primary. I have used electric hob heating elements. Cheap, cheerful, high ampacity, and utterly indifferent to the modest bit of heat before they are bypassed.

C) Even once up, a 10 HP idler "may" still need the load-motor on the output side of the transformer "soft started" as well.

Long and short of it is that smallholder power distribution budget in Blighty is a mere fraction of the KVA riches we enjoy in the energy-profligate USA. The protective devices are more paranoid, accordingly. Can't be helped. Prepare to "JFDWT".

thermite said:

B) Place a "soft start" between the RPC idler and the transformer primary. I have used electric hob heating elements. Cheap, cheerful, high ampacity, and utterly indifferent to the modest bit of heat before they are bypassed.

C) Even once up, a 10 HP idler "may" still need the load-motor on the output side of the transformer "soft started" as well.

Click to expand...

Dealing with a similar problem discussing in another thread. Does someone have a link to a "soft start" device that would work in this application?

adh2000 said:

Dealing with a similar problem discussing in another thread. Does someone have a link to a "soft start" device that would work in this application?

Click to expand...

Current-limiting by placing resistors inline (series) at start, then "shunted" (paralleled AKA bypassed) right SOON thereafter..lest they damage the load from being too short of power.

Resistors that can handle the power exist, but are expensive!

Electric cooker elements are also resistors, and generally cheap. Relatively, anyway.

They also will not "burn up" even at FULL power, because it is their "job" to get hot, so they are "built for it!"

In soft-start service they generally do not have TIME to get hot, and aren't under full load, anyway. The load current-limits the resistor less than the reverse, but limit "somewhat" it still does, nonetheless.

JST said:

Are you switching the transformer into the circuit after the converter is running? That is the right way t do it. Having it connected to the converter when converter is started will draw a lot of current and not work.

Click to expand...

This is a good point for anyone working with RPCs, they should always be started unloaded.