3 Phase VFD supplied by single phase - de-rating

[Smouser]

Has anybody successfully powered a 3 phase input VFD from a single phase supply by de-rating the drive?

The situation is as follows:
1. I need to power a 3 phase - 230v - 3kw motor (wired in Delta).
2. I only have single phase supply available.
3. I have got an ABB ACS 355-03E-15A6-4 (7.5kw) VFD. It has been designed for three phase power input.

I have read on a few sources that a 3 phase 'only' input VFD can in theory be powered by a single phase supply but the drive/VFD needs to be de-rated by a minimum of 50%.

In theory my 7.5kw ABB VFD will then become a 3.75kw VFD, enough to power the 3 phase 230v 3kw motor (3.75kw will obviously be too much for a 3 pin, 13A plug so I will wire the supply direct from a MCB with the appropriate thickness cable).

There is some VERY limited information here.

Has anybody successfuly de-rated a 3 phase input VFD so it can be run on single phase?

Specifically interested to know if it has been done on an ABB ACS355 drive.

 

[Agroshield]

How much does the VFD owe you?

Just try it and see.

This is not being cavalier (or chevette for that matter). The VFD has enough brains to it to detect multiple problems on both its input and output and go into a fault mode as required.

If it works on the bench, bolt the motor down and apply a piece of timber to the shaft until it is well loaded (approximating 50% overload of normal running) and see what happens. Decide if you can live with that situation.

 

[minimutly]

Most “clever” ie modern units will detect a low dc bus voltage and fault out. If you can access this and reduce the setting it will usually work. Very few drives manuals give you this data.
The other way to do it is to create your own dc at the correct voltage (around 500V) using a voltage doubling diode and capacitors, and feed this into the dc bus of the inverter - again you need some detailed knowledge and some access to adjustable settings. This is how my Fritz Werner is run. Care needed when testing....
One thing I’ve not tried is to transform the ac up - so the inverter dc bus voltage is closer to normal - you use the transformer outputs across two of the input phases. A 240/110 transformer in reverse might be an inefficient way, but it might work?

 

[Pete.]

I tried it once on a Jaguar VFD and all I got back was a phase loss error.

Didn't look any further into it.

 

[Smouser]

The ABB drives are pretty clever with LOADS of parameters. It might just be a case of reading the manual in detail to find the required parameters to de-rate the drive.

The reason I got this drive was twofold.
1. I like the ABB drives and I know the single phase input versions pretty well (I have got 4 of them).
2. I got it for an absolute bargain price and I will be able to sell it on, make my money back and have a little profit if turns out it is unsuitable.

I am working away this week but hope to get a chance on the weekend to test things out.

 

[minimutly]

It’s not about de-rating, it’s about adjusting the phase detection out so the drive ignores the missing and lower voltage - basically removing some of its protections. I have some ABB ones designed to run on 500VDC - they may be different, but they may also just be the same with certain parameters removed. Truth is I don’t know.

 

[Smouser]

I tried it once on a Jaguar VFD and all I got back was a phase loss error.

Didn't look any further into it.

Thanks Pete.
It would seem that some 3 phase VFDs can be 'easily' set up to take 1 Phase supply, other might need many parameters changing and some might not be able to it it all.

It’s not about de-rating, it’s about adjusting the phase detection out so the drive ignores the missing and lower voltage - basically removing some of its protections. I have some ABB ones designed to run on 500VDC - they may be different, but they may also just be the same with certain parameters removed. Truth is I don’t know.

Thanks minimutly. Testing and playing with the VFD to see if it can be done seems to be the approach I need to take.

I will report back with my findings.

 

[Smouser]

Some information on the ACS550 de-rating. That does not mean it applies to the ACS355 drives but it gives me hope.

 

[knighty]

1. I need to power a 3 phase - 230v - 3kw motor (wired in Delta).

are you sure it's 230v in delta?

most are 230v in star and 415 in delta?

 

[Pete.]

are you sure it's 230v in delta?

most are 230v in star and 415 in delta?

Other way round. Star puts windings in series so you need the higher voltage to achieve the same wattage.

 

[knighty]

in star each winding is wired live to centre point

in delta they're wired live to live - so across each winding

photos from google - I googled to check I'm right, I am (I'm no expert)

 

[Smouser]

Your images are correct.
However, Delta = low voltage and Star = high voltage on 'normal' three phase motors.

 

[knighty]

from google....

In star connection, each winding receives 230 volts and in delta connection, each winding receives 415 volts

with 230v on each phase, in star they all terminate at the centre point, sum of all the phases - 0v so there's 230v across each phase

in delta they're all 230v to 230v, phase to phase, so 415v across each phase?


they're always 230v fed in on the phases, voltage across the windings depends how they're connected?

 

[Smouser]

I am not going to pretend that I know EXACTLY how it works but if you google images 'three phase motor data plate' you will see that Delta is the lower voltage and Star/Y/Wye is the higher voltage.

Here is a couple of examples

 

[Pete.]

from google....



with 230v on each phase, in star they all terminate at the centre point, sum of all the phases - 0v so there's 230v across each phase

in delta they're all 230v to 230v, phase to phase, so 415v across each phase?


they're always 230v fed in on the phases, voltage across the windings depends how they're connected?

Yes that's true but you're confusing yourself by talking about winding voltages. Think about motor power and input voltages instead.

See here the star connection is 380-420v and current is 3.50A Power is 1.5kw. Delta connection is 220-240V and 6.10A. Power is still 1.5KW

Because the star connection has two windings in series beween each input phase, it requires higher voltage and lower current to produce the same power because the windings are in effect two big resistors in series. In Delta formation you have two series windings in parallel with one single winding which means lower resistance between phases. Less voltage required and higher current to produce the rated power.

Old star-delta starter systems used to take advantage of this by having the delta winding rated at line voltage (usually 415v) and the star windings rated at higher voltage (for example 400/690v motors). They would have a change-over contactor that started the motor in star (effectively well below rated voltage to reduce the start-up current) then switch over to delta once they were spun up (to give full power at the rated voltage).

https://www.electrical4u.com/star-delta-starter/

 

[Kram]

(3.75kw will obviously be too much for a 3 pin, 13A plug so I will wire the supply direct from a MCB with the appropriate thickness cable).

Your motor is 3kw. If you set a sensible overload limit, and depending on the usage, you'll likely be well below the 3.2kw of a 13A plug 99% of the time. Lathe will be a low load. Compressor or similar might be much nearer the 3kw rating. Worst that can happen is you'll pop a 13a fuse. I'd have no problem with 13a plug.

in star each winding is wired live to centre point

in delta they're wired live to live - so across each winding

photos from google - I googled to check I'm right, I am (I'm no expert)

I can see why the confusion, ignore the central star point/ neutral connection shown in your star pic, vfd's dont use it. Delta has one winding between each phase while star has two in series.

 

[Dave-sparks]

in star each winding is wired live to centre point

in delta they're wired live to live - so across each winding

photos from google - I googled to check I'm right, I am (I'm no expert)

Your star diagram is incorrect, you don't have a neutral connected to the motor, just the 3 phases.

If the motor is configured for star then the input voltage is applied across 2 windings in series therefore can be higher than the delta input voltage which is applied across a single winding.

So for the motors rated voltage it will always be higher in star.

You may be confusing this with a setup where you intentionally run a star connected motor at less than its maximum rated voltage, such as star/delta starting.

 

[carbon]

Your star diagram is incorrect, you don't have a neutral connected to the motor, just the 3 phases

You can use the star point as a neutral to run other 240v device’s from when the motor is running when connected to a 415v supply

 

[knighty]

as above, I have a neutral point connected on lots of 3 phase motors - mostly because I'm wiring them up with 5 core cable and it's there so I might as well use it

guess it'll help if one winding ever starts to deteriorate

force of from habit when I'm connected up 3 phase heaters - inevitably 1 heater will die and throw the rest out of whack... connect the neutral to what's essentially the centre point and the rest will keep on working just fine.


I think my confusion is the difference between and winding resistances and the actual real world voltages everyone uses?

in real world situations, star is 230v per winding and delta is 415v per winding... because everyone's mains power is has 230v x 3 phase




(I get that there may be weird specific or HUGE motors using oddball/higher voltages)

 

[Guineafowl]

I think my confusion is the difference between and winding resistances and the actual real world voltages everyone uses?

in real world situations, star is 230v per winding and delta is 415v per winding... because everyone's mains power is has 230v x 3 phase

A bit of terminology might (or might not!) clear things up:
For a typical 415/240 UK setup:

In star:
The LINE voltage (between R-Y-B) is 415V
The PHASE voltage (all to N) is 240V

In delta:
LINE and PHASE voltage are the same. If supplied by above then both 415V.

Winding RESISTANCE is not very interesting, because with ac you consider the IMPEDANCE, which is usually a complex number, and when adding two windings in star you have to consider the 120deg angle between them.