Three Phase Dual Voltage Motors.

[Station X]

Today I came to connect my ancient Rapidor Power Hacksaw to the mains supply. It has a one horsepower three phase motor. On the maker's plate it says 230/250V 3.3A and 380/440V 1.9A. Nothing unusual in that, I've seen similar plates dozens of times before.

Under the lid of the motor's terminal connections is a wiring diagram. The motor is identified as THREE PHASE DUAL VOLTAGE. The diagrams show that for high voltage the motor is wired in Star and for low voltages it's wired in Delta (without a neutral connection). It's presently wired in Star and it'll stay that way. No point in using Star/Delta switching on such a small motor.

I inspected a few more motors and they all had similar diagrams, but they didn't specifically identify as dual voltage motors. The exception was a 3/4 horsepower motor with only three (not six) wires brought out from the windings. This was 440V only and I assume permanently wired in Star.

My questions are these:-

1. Is a dual voltage three phase motor just another name for a three phase motor which can be wired in Star or Delta, or is such a motor designed for use on 230V three phase supplies?

2. Why do small three phase motors have the Star/Delta option? Why not just have them permanently wired in Star?

To dispel any misconceptions. I'm not trying to connect this motor to a single phase 230V domestic supply. I have a rotary convertor to generate a three phase 440V supply. I'm familiar with the terms phase and line voltage when it come to three phase supplies, so no need to explain these.

Thanks.

[dseymo1]

I don't know, but would guess that the answer to (2) is to provide flexibility to accommodate the most conveniently available voltage.

[1100 man]

Originally Posted by Station X

My questions are these:-

1. Is a dual voltage three phase motor just another name for a three phase motor which can be wired in Star or Delta, or is such a motor designed for use on 230V three phase supplies?
2. Why do small three phase motors have the Star/Delta option? Why not just have them permanently wired in Star?

Hi Graham,

If it's specified as dual voltage (220/230, 380/440) then it can only be configured in star on a 440V supply. If configured as delta, on 440V, it will go pop!! So you can't star/delta start such a motor on 440V. You could do so on a 220V three phase supply if you so wished.

Most small motors rated for single voltage usually have the terminal box already configured for what the maker intended and only three line connections.
Obviously, all six connections will be present in the terminal box anyway though.
Hope that helps,
All the best
Nick

[Station X]

That certainly does help Nick.

Are 220V three phase supplies available in the UK though? I know that Variable Frequency Drives (VFDs) supply 220V three phase and I've restrapped three phase motors to use this. This motor must predate the use of VFD's by at least half a century though.

[Radio Wrangler]

In making a motor, you don't want wiring joints buried in the windings, so you bring out both ends of all three windings, so you get the star/delta reconfigurability essentially for free.

There were VFDs around a long time ago - based on thyratrons, but not really common enough for motors to be influenced much.

David

[1100 man]

To my knowledge, the UK has never had a public 220V/3ph supply. However, some other parts of the world do have. With an old motor, though, I wonder if some rotary converters might have been 220V/3ph and so they would have been used with those in small factories perhaps?

I learnt the hard way about dual voltage motors many years ago. I had just had a small 3ph motor re-wound and re-fitted it to the coolant pump of a milling machine. Without thinking, I just wired it in delta There was a big flash when I turned it on and back it went for another re-wind!!

All the machinery & control gear I've worked on has always been 380V (nominally measured). I don't think any public supply in the UK is now 440V/3ph.

Cheers
Nick

[julie_m]

Some Continental supplies used to be wired as 127V phase-to-neutral, 220V phase-to-phase; I think the same arrangement may still be used in some South American countries.

The UK has been 240V or 230V phase-to-neutral and 415V or 400V phase-to-phase as long as I have known, though some universities used to (and probably still do) have their own 127/220V power circuits in the electrical engineering department.

[barrymagrec]

220 volt 3 phase supplies were often used in the Film business, presumably to line up with the US.
I have seen a lot of step down transformers in Film places to provide the supply.

[Bobdger]

230/3/50 / 415/3/50 motors are normanly up to 3hp then above 4 hp the windings are 415/3/50 / 690/3/50 these are normaly used with star delta starters. The low hp motors that are dual wound are very usful as you can use a 230/1/50 inverter for speed control this gives an output of 230/3/50. The price of small inverters have dropped to a very low price now making them a standard fitting in a lot of pump set.

Bob.

[ex 2 Base]

Dual voltage are sought after by Model Engineers when converting single phase machines, lathes or milling machine from single phase to three phase via an inverter. As descried on the terminal box lid it's quite easy to carry out the conversion. It's not so difficult to locate the STAR point either when the motor is dismantled and bring out the extra 3 leads into the terminal box. Extra care should be taken when insulating the junction stator winding/ to new leads. There has been much discussion on the Model Engineer web site about such motors and inverters. Ted

[dseymo1]

I worked in a place here in the UK which I'm pretty sure had 230V three phase outlets (4 pin metalclad with a screw collar, gauge similar to domestic 5A). They were never used in my time there though.

[1100 man]

That sounds like a standard 15A 3 phase socket made by Lewden. They are still available and were a fairly common standard before the red plastic 4 & 5 pin sockets took over.
Most 3 phase stuff doesn't need a neutral so the 3 pin plus earth pin is the most common type.
Standard 380/415V 3 phase use. There is also a 5A version with pins similar to a 5A plug.

Cheers
Nick

[MotorBikeLes]

I am afraid things are not always that simple. If a motor is marked 230/415v 3Ph, then it will be exactly as Graham's originally cited motor.
Many older motors were marked 415v 3ph, and only had three terminals as previously stated. However, they may NOT be 230/415v motors with a hidden star point. Generally when you get above about 3HP, then it is more likely that it is a HIGHER voltage motor connected in delta. There will be three hidden joints where this configuration is achieved. Traditionally in the UK when people speak of "star/delta switching", you have a 415v/750v motor. As I mentioned, get above 3HP, and 3 wire 415v motors are probably this sort.
Of course star/delta switching is much less common these days as it is not too expensive to use a 415v to 415v three phase inverter, and a slow start up will obviate the reasons for star/delta switching. (ie, you don't draw high current, overloading switches, wiring, and burning out the motor itself.
The sketch is a data plate from the motor used in a 16HP rotary phase converter.
Les.

[McMurdo]

just to confuse matters, some 230/415 dual voltage motors can be run on an inverter fed from 415V for lathes and other machine tools where you want low speed, high torque and high speed, low torque ('constant Horsepower') without the trouble of a gearbox. You set the inverter base frequency to deliver 415V at 86.6Hz and then connect the motor in delta.

This sounds esoteric but is standard practice in Colchester/Harrison and other lathes and has been since the late 1980's.

It's also used to squeeze extra performance out of underrated motors, or, as the sales pitch goes, to allow the economical use of a motor one frame size less than that normally dictated.

[MotorBikeLes]

I see some of what I wrote had already been provided by Bob, sorry, I missed that.
Graham also asked in #6 about 230v three phase supplies. Many hobby-ists create 3 phase supplies by feeding 230v to a three phase motor, with a capacitor or capacitors. Either to simply drive the motor, or as a rotary converter to (better) drive the work motor. That same system, but fed from a 230v to 415v transformer (or auto transformer), gives a 415v three phase supply. Again it could be a STATIC converter, or a rotary phase converter.
Les.

[broadgage]

As has already been said, standard smaller types of dual voltage 3 phase motor are suitable for star connection to a UK type 3 phase, 4 wire system at 230/400 volts, and are also suitable for delta connection to 3 phase 4 wire systems at 133/230 volts and also for 230 volt 3 wire systems.

A few parts of the UK did have 3 phase systems with only 220/230/240 volts between phases. I very much doubt that any such systems remain.
Many parts of Europe had similar systems and some no doubt remain in use.

Continued production of such motors is still worth while for countries with 3 phase at lower than UK voltage, and for operation from inverter drives.
Some USA supplies are 3 phase 240 volts between phases, and with the mid point of one phase earthed to give a neutral.

Larger three phase dual voltage motors are often equipped with 400 volt windings. These may used delta connected on a standard UK 230/400 volt system, or may be used star connected on a 3 phase, 4 wire system at 400/690 volts, or on a 3 wire, 3 phase system at 690 volts.

400/690 volt systems are increasingly popular for physically extensive works such as oil refineries, large factories, and sewage treatment plants in order to reduce cable sizes.

The use of dual voltage motors for 690/1200 volts has been tried but found little favour since 1000 volts is now the limit of low voltage in many countries.

If 690 volts is judged insufficient, then one might as well go up to 3,300 volts, an already popular voltage.

[Station X]

Thanks to members who have contributed to this thread.

I now know exactly what a dual voltage three phase motor is. I had misled myself because I was familiar with larger motors which could be connected in Star or Delta and I was unaware of the existence of 230V three phase supplies.

The motor in question is a totally enclosed type with a fan on one end of the shaft and a reduction gearbox on the other. It was manufactured in 1962. It won't be running for a day or two though, as the mains flex is too short for my requirements and needs replacing.

The existing flex has an interesting colour code. I'd have thought that the brown wire should have been yellow. The black wire, rather than the blue is used as neutral. A neutral connection is needed to supply 230V to the contactor coil of the Direct On Line Starter which incorporates a three pole isolator.

[broadgage]

I think that the brown core might actually be intended to be brown.

After the introduction of green/yellow for earth, there was a prohibition on mains voltage flexibles containing "a green core, or a yellow core, or any bi colour other than yellow/green"

I suspect that the flex is relatively new and was intended to be used with blue for neutral, and brown, black and red for the phases.
Brown and black were well established as phase colours in Europe, and red was sometimes used for the third phase, though two brown cores and one black, or the other way round was more common.

Whoever fitted it obviously followed the UK convention, so far as possible.

[Station X]

That makes sense broadgage.

Success. The motor and saw are now running nicely.

The new flex had a yellow/green wire and four black wires labelled 1 to 4. I used wire 4 as neutral, marking the ends with blue tape. Wires 1 to 3 were used for L1, L2 and L3. When used with the rotary convertor the 230V contactor coil has to be connected between neutral and L1, so I made sure that was right first, then connected L2 and L3.

As you can probably guess the motor then ran backwards, so I changed over L2 and L3 going to the motor so as to keep the correct wiring notation at the input to the starter/isolator.

[Radio Wrangler]

Theoretically, you should have a 50% chance of the direction being right. As we all know things turn out far less successfully than this, thereby proving an element of malice is integral to our universe.

All that invisible missing mass was just put there to confound cosmologists.

David