Auto transformer/rotary phase converter

The intention is to feed this auto transformer with 230 volts from rotary phase converter. Will it work if I disconnect all reference to ground!View attachment 2

Don Gitzel said:

The intention is to feed this auto transformer with 230 volts from rotary phase converter. Will it work if I disconnect all reference to ground!View attachment 2

Click to expand...

Hammond catalog is online. If you cannot get a useful foto, post the part number so we can look up Hammond's specs and schematic.

Meanwhile... not YET a certainty you are good to go . we may need info on the REST of the environment and what you are up to.

But ..there isn't necessarily ANY "ground" (nor a Neutral..) involved with a transformer ... auto OR full isolation ... except to the CASE . .for safety. Otherwise "it depends".

The intention is to feed 230 3 phase from a rotary phase converter into the low voltage side of the auto transformer X4-X5 & X6 and get 600 volts out of H1-H2 & H3 to feed a machine.

Read the code handbook. If you are at all unsure about this, hire a licensed electrician. If you don't have a ground reference on the RPC output or the 600-V output, those voltages are unpegged relative to ground. You need a ground reference for the 600-V side. Make sure the grounded leg has no fuse in it, and that the two 600-V hot legs do. Most likely, you will want to ground one corner if 600-V delta. On the RPC side, the ground reference is halfway between the two original single-phase hot legs.

Don Gitzel said:

The intention is to feed 230 3 phase from a rotary phase converter into the low voltage side of the auto transformer X4-X5 & X6 and get 600 volts out of H1-H2 & H3 to feed a machine. View attachment 295604

Click to expand...

I have a STRONG personal aversion to use of an "autotransformer" for more than 25% boost.

You are goaling for 260%? Two-point-six times?

Not my cuppa.

I want full isolation. I get full isolation. It provides for more and better choices. Done well, it can be safer.

With regard to grounding....

First, you absolutely cannot ground the X0 connection, because the output of a phase converter is NOT balanced to ground, and this is an autotransformer, which is not isolating.

The phase converter puts out wild leg 3 phase, which is grounded at the center tap of the source 230V. That is NOT the center of the 3 phase output.

So:

1) the output does NOT form a "separately derived source", so rules on grounding such a source do not apply.

2) The center "X0" is NOT at ground potential, it is at a substantial voltage to ground, so in any case it cannot be grounded.

3) None of the wires from the phase converter can be grounded either, they are all at a voltage to ground, so corner grounding is not possible.

4) The source for the 3 phase converter IS grounded, and that will supply the ground reference for that entire circuit. No further grounding is allowed.

Bottom line: Do not ground any connection of the phase converter or this transformer. The bonding is (or had better be) back at the service box, and no further ground connections are necessary (nor are they allowed).


Edited to change "part" to "connection". You DO want to ground the enclosure, as always, using the equipment grounding conductor (green wire)

You need to connect the x0 "neutral" of the auto transformer to the y neutral point of the rpc. (T 4 5 6 for a 9 wire motor)

While it would be better if you could get to both y points of the rpc, one will suffice for a minimally unballanced load.

Alternatively you can find a 1:1 ratio 3 phase transformer of any voltage higher than 200 volts, reconnect it as a zig zag transformer, and connect it across the auto transformer.

If you only have a 440 or 600 volt motor to run and nothing else then you leave x0 disconnected. Otherwise any imballanced load is undefined and even a 100nwatt control transformer will pull the voltage of 2 legs down until the other leg of the transformer saturates.

JST said:

With regard to grounding....

First, you absolutely cannot ground the X0 connection, because the output of a phase converter is NOT balanced to ground, and this is an autotransformer, which is not isolating.

The phase converter puts out wild leg 3 phase, which is grounded at the center tap of the source 230V. That is NOT the center of the 3 phase output.

So:

1) the output does NOT form a "separately derived source", so rules on grounding such a source do not apply.

2) The center "X0" is NOT at ground potential, it is at a substantial voltage to ground, so in any case it cannot be grounded.

3) None of the wires from the phase converter can be grounded either, they are all at a voltage to ground, so corner grounding is not possible.

4) The source for the 3 phase converter IS grounded, and that will supply the ground reference for that entire circuit. No further grounding is allowed.

Bottom line: Do not ground any part of the phase converter or this transformer. The bonding is (or had better be) back at the service box, and no further ground connections are necessary (nor are they allowed).

Click to expand...

Write this one on the wall, Brethren. J? Might modify that a tad and make it into a "Sticky" put right at the head of the list for the forum?

My RPC outputs to a Delta-in, Wye-out EGS Hevi-Duty 1:1 ratio "Drive Isolation" transformer.

This "challenge" is why.

So I CAN re-derive a "LOCAL" Neutral. And bond it if/as/when/where appropriate.

Phase Technologies specifies a Delta-Wye full isolation transformer used exactly the same way for the "semi-floating" Delta output from a Phase-Perfect intermediary to that center-tap-Earth-bonded Neutral split-phase source. "RTFM". No free lunch. Same challenge as an RPC presents. Yah dare NOT Earth either of the legs common to the feed.

Given I have BOTH of a P-P and RPC? My isolation transformer serves "either", actually. A Square-D transfer switch insures that is not just "OR', but "XOR".. "exclusive OR" as well. A not B. B not A. Never both.

Dunno if it is possible to sync and parallel an RPC with a Phase-Perfect or not. But I am surely not he to place an all or nothing $4,600 BET on the outcome!

Cheaper to presume "F**K NO!"



Pain in the pocketbook, that fat transformer? Only "slightly" at used-but-good prices.

"That's a feature, not a bug."

Were else would one RATHER take the hit and the pain?

At a higher potential to Earth, perhaps hand to hand, across yer heart?

No Fine Way, thanks!

"Leg to leg" is still aways THERE. No free lunch on that.

A tad under 140 VAC, any leg to Earth as MAX? Well... that can still be lethal.

But at least it improves my odds of survival should I get stoopid or careless!

That shall have to do.

johansen said:

You need to connect the x0 "neutral" of the auto transformer to the y neutral point of the rpc. (T 4 5 6 for a 9 wire motor)

........

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That would be fine, but that point may be unobtainable, depending on the idler. if you CAN get to the idler star center, that would be fine, and can help as described. Note to others (Johansen knows this) that point is NOT at ground potential, and the resulting "neutral" is NOT a "grounded neutral". It is for balancing purposes only.

Don Gitzel said:

The intention is to feed this auto transformer with 230 volts from rotary phase converter. Will it work if I disconnect all reference to ground!View attachment 2

Click to expand...

there is a ground on the base of the frame, it has a green screw.

the picture of the 4th leg is inside the transformer, dont use it! it still has voltage. they basically connect all the legs between each winding to make a WYE connection. Its only there to make 277V, single phase of 600 V to neutral.

if not sure, get an actual elechicken!

I'm watching to see how this thread develops.. partly tempted to re-motor my own lathe and mill in the UK.