If no neutral wired to machine, can I use Delta source (Phase Perfect)?

[StoneMachines]

Hello,
Looking for some guidance on supplying power to a machine.

Power Source - Typical North American residential single phase 240volt.
Machine requirements 480v 3 phase.
Was hoping to use a Phase Perfect with the voltage doubling feature so I do not need a transformer.
The manual for the machine to be powered shows, and the physical input terminals only have, 3 wires + ground

However the machine manual states:

The use of three phase power with delta connection (as sometimes used in North
Americas and some Asian countries) voids warranty. If the facility has a substation
with any type of delta connection, a grounded Y-configured transformer must be
installed before the robot controller

This is a used machine well out of warranty, but I don't want to damage anything.

If the machine doesn't require a neutral why would the manual state this?
I've looked at the schematic.
This is the input terminal connection:

From there to an internal transformer (right side):


It does show a 115v circuit on the output of the internal transformer, but referenced to ground not a supplied neutral. From the transformer some 230v single phase circuits go to DC power power supplies. The 480v 3 phase is passed to a rectifier

The only place the internal generated 115v/internal neutral go to are a service port, which could be disabled if that is the only thing requiring reference to ground.

If I took care to wire the "pass through" (non generated legs) of the phase perfect to the terminals (appears to be L1, L2) that feed the 230v single phase power supplies I should be OK? The rectifier shouldn't be affected by the high leg?

My understanding is that the Phase Perfect supplies a delta source (from their FAQ):
Why is the output voltage on one leg of my 240 V phase converter 208 V to ground?

A: For a phase converter to generate three-phase power, the two incoming power lines are directly passed through to the output and the phase converter generates the third leg in a configuration known as “high-leg delta.” This will power most three-phase machines. Some machines however require wye-configured power, which includes a neutral. If your machine requires wye-configured power, you will need to send the output of the phase converter through a delta-to-wye transformer before the load. In the graphic below, T3 is the generated leg.

Figure 2 – High Leg Delta



I know just buy the right transformer, but money

Thanks
Greg.

 

[JST]

Services are required to have a ground reference. In a delta system, the only way to do that is to corner ground (ground one supply line), or ground a tap on one winding (stinger, or high leg 3 phase). The voltage to ground is then different for different wires.

Corner ground has the full voltage to ground (480VAC here)on two wires, high leg three phase has an intermediate voltage to ground on one wire, and wye has a voltage to ground that is considerably less than line voltage (about 277 VAC here). There is a class of wiring rated 300VAC or less, and a different class for 600VAC.

Since that unit uses an autotransformer, rather than an isolating transformer, delta connected input will provide a higher voltage to ground inside the machine, which may be undesirable due to ratings of parts, etc. There are 230V outputs, so there are lower voltage devices in the unit, which may not have sufficient insulation.

Also, a transformer fault, such as a winding becoming disconnected at one end, will apply a higher voltage than the nominal to whatever is connected to the lower voltage taps.

The Phase Perfect puts out high leg delta, so it is a prohibited source for this machine, the high leg would be around 410VAC to ground.

 

[SomeoneSomewhere]

It's also an issue for surge protection, line filtering, and overvoltage suppression. If there are caps/MOVs to ground (very common), then they are likely designed for 277V nominal and rated at, oh, 325V?

Supplying it from a source that might have 400-480V to ground will cause those parts to fail immediately.

 

[StoneMachines]

The Phase Perfect puts out high leg delta, so it is a prohibited source for this machine, the high leg would be around 410VAC to ground.

It's also an issue for surge protection, line filtering, and overvoltage suppression. If there are caps/MOVs to ground (very common), then they are likely designed for 277V nominal and rated at, oh, 325V?

Supplying it from a source that might have 400-480V to ground will cause those parts to fail immediately.

OK, so I'll need a Delta to Wye transformer of some sort, so it's probably not worth getting the voltage doubler feature (an extra $1000) of the Phase Perfect, and instead put that money towards a step up delta-wye transformer to go between a non voltage doubling Phase Perfect and the machine?

 

[rons]

OK, so I'll need a Delta to Wye transformer of some sort, so it's probably not worth getting the voltage doubler feature (an extra $1000) of the Phase Perfect, and instead put that money towards a step up delta-wye transformer to go between a non voltage doubling Phase Perfect and the machine?

Voltage doubling is just an arrangement of 2 capacitors and 2 diodes.

 

[jim rozen]

"instead put that money towards a step up delta-wye transformer to go between a non voltage doubling Phase Perfect and the machine?"

Agree. Do that.

 

[Strostkovy]

Tangentially related but I hate the convention of dumping fault currents through the EGC. That's literally shunting excessively high currents to the chassis of your machine. If the ground has a slightly high resistance connection then your machine becomes very live briefly. Dump fault current between current carrying wires such as phases or neutral.

 

[sfriedberg]

Voltage doubling is just an arrangement of 2 capacitors and 2 diodes.

No, no, no, no. "Voltage doubling" here is talking about 3-phase AC voltage, requiring a transformer. The discussion is not about generating pulsed DC from single-phase AC.

 

[StoneMachines]

"instead put that money towards a step up delta-wye transformer to go between a non voltage doubling Phase Perfect and the machine?"

Agree. Do that.

Thanks everyone!

 

[JST]

The Phase Perfect only "converts" one line, so while it could indeed make THAT 480 output from 240, the other two lines still would need boosting.

Transformer is needed to use with regular 240V PP.

They do have doubling types, and use no transformer. I assume they act similar to a VFD, converting all 3 lines, with a common boost converter up front. What I do not know is whether they would output a wye type voltage. The standard PP produces high leg 3 phase, and I would assume without further information that the output of the doubler type might be "offset" relative to the incoming neutral.

If you still need a transformer to get wye output, then you may as well use a delta-wye boost transformer and a 240V PP.

As for the grounding and EGC......

The reason for using the EGC is that it connects to the ground rod, AND some of the possible faults involve the opening of the neutral, for whatever reason.

The ground rod ensures that the EGC is at earth potential, or close to it. The EGC is required to be of a size to avoid excessive voltage drop, so the earth you are standing on and the chassis are at as close to the same potential as possible. And, there is no other current in the EGC to add to the voltage drop.

There is no choice that can provide absolute protection against a really serious fault, such as a power cross from a 13,000 volt feeder to the EGC. But the EGC protects as well as is practical against faults in the protected equipment, which is what it is for.

 

[rons]

No, no, no, no. "Voltage doubling" here is talking about 3-phase AC voltage, requiring a transformer. The discussion is not about generating pulsed DC from single-phase AC.

There would be three separate doubling circuits for each phase. The incoming AC is rectified and fed to two capacitors per phase.
The caps are in series with now double the voltage across both of them. This raises the DC bus to double potential of what it would have been with no x2/
That's what I'm talking about.

 

[JST]

They already have a regulating and power factor correcting boost converter inside most of their units. That can boost to any reasonable voltage, and that voltage can supply 3 phases as easily as one.

The boost versions are available in the "enterprise" units, which do have the PF correcting section. So, zero need for capacitor type voltage doublers (that incidentally have a horrible power factor).

 

[sfriedberg]

This raises the DC bus

My apologies. I thought you were talking about substituting a DC voltage doubler for the delta-wye transformer under discussion for the output side of the PP.
I've never seen a diagram for the voltage-doubling PP models, but the original (blue) generation of PPs did regeneration, where excess current (e.g., from a downstream motor being braked) was pushed back toward the supply instead of wasted in a resistor bank. Is that consistent with an internal DC bus? I can't imagine they used downstream and upstream inverters.

 

[Strostkovy]

My apologies. I thought you were talking about substituting a DC voltage doubler for the delta-wye transformer under discussion for the output side of the PP.
I've never seen a diagram for the voltage-doubling PP models, but the original (blue) generation of PPs did regeneration, where excess current (e.g., from a downstream motor being braked) was pushed back toward the supply instead of wasted in a resistor bank. Is that consistent with an internal DC bus? I can't imagine they used downstream and upstream inverters.

The pass through phases will always accept power backwards.

Given only one phase needs to be generated to back feed the single phase supply, it may be not that much more costly to add that to keep the DC voltage down instead of adding a resistor and the associated control circuitry to tame the energy backfed on the generated phase.

 

[thesjg]

The Phase Perfect only "converts" one line, so while it could indeed make THAT 480 output from 240, the other two lines still would need boosting.

That is true of the rest of the Phase Perfect line, the voltage doubling PTE models create two legs, not one.

 

[JST]

That is true of the rest of the Phase Perfect line, the voltage doubling PTE models create two legs, not one.

That would indeed be all that is needed. (see post 12).

It seems that then the effective neutral for the output would be well off ground, so to get a wye output there would still need to be an isolating transformer.

Is the output then like a corner grounded 3 phase? Or is the remaining unboosted leg one of the supplied phase wires?

Knowing that could be important for some equipment, particularly if it includes any transient protection. Corner grounding usually needs the transient protection removed due to the high "to-ground" voltage. It would require all the insulation to be of the next voltage class up from the 300VAC max to ground class that is OK for 480 wye (which has 277 to neutral).