Electric Motor Configurations

Perhaps "wired in star" means "wired in star when supplied" and not "must remain in star"  It should be fine if connected in delta on a three phase supply with 220 volts between phases. 

If for some odd reason this motor must not be wired in delta, then provision of a terminal box that facilitates changing to a delta connection seems unlikely.

If use in the UK is contemplated then the frequency difference is more important. Running a 220/380 volt motor and our supply which is still 240/415 volts in practice is a bit marginal. Running a 60 cycle motor on 50 cycles is also marginal. Running a 220 volt 60 cycle motor on 240 volts 50 cycles may end badly.

Thanks Broadgate.

The motor will be used in the UK... but hiding behind a single to three phase inverter drive. I want a final speed of 0 - 3600 rpm hence using a 2 pole 60Hz motor. Obviously the inverter, being supplied from 230V single phase can only give 230 phase to phase out, so my plan was to flip the motor into delta & power it from the inverter.

Use from an inverter as described should be fine, but double check that the motor can not be subjected to excess voltage and low frequency at the same time.

230 volts at 60 cycles should be fine as it is within the reasonably expected range for a nominal 220 volt supply.

250 Volts at 60 cycles might be a bit much.

200 volts at at 50 cycles should be OK, As it is only slightly in excess of the nominal volts per cycle. 230 volts at 50 cycles is probably a bit much much.

Oddly I have a friend doing something similar with great success from well below 50Hz to about twice it - the good VSD inverters can be programmed to drop the effective peak voltage as the frequency drops. In reality it is modulating the mark to space ratio of a square wave but the motor windings are only heated in more or less the normal way as per the fundamental component of the waveform
I suggest a campaign of just doing it - if you are that bothered put something in series with the windings, like 3 identical heaters. You should be able to get it spinning and verify rotation directions, and ramp up and braking times etc at quite a lot less than the full voltage if it is not loaded. I;d not be too worried about the labeling - clearly the windings are insulated from each other, all you need to do is get 3 lots of magnetic field rising and falling in the right sequence.

If you badly overdo the voltage or underdo the frequency (more or less equivalent) the current will rise sharply more than linearly beyond a certain point, and the current limits need to be set sensibly so that the windings are not cooked.

The other parameter to consider is the back EMF when decelerating - an over-voltage high enough to damage the inverter can occur in some cases if you try to force a dead stop unless there is somewhere for it to go (a braking resistor) in the drive arrangements.

Mike

The motor was probably supplied for Star duty - check the kW rating; connecting it in Delta would require a Delta rating. The reason why motors are Star/Delta connected, is to reduce the starting current (and torque) by starting in Star, these are both increased by a factor of 3 when switched to Delta. Connecting a motor designed for Star connection in Delta will burn out the motor windings - toot suite. Speed in RPM will be same in both modes. 60Hz signals a US design.

Jaymack     

No, this is getting very odd. A 3 phase induction motor can obviously run as star or delta, the windings get exactly the same everything, the only difference is that the voltage applied for operation will have to be changed so that the winding currents are equal for either connection. So a 400 V star-connected motor will operate correctly with 1/root 2 times the voltage, that is 230V in delta. There is no difference whatsoever in the motor design, the heat or winding currents, or mechanical power. Star-delta starting is a red herring, the motor must be rated for 400V delta operation, the star starting just reduces the start current substantially.

Running motors from VFDs can have some effects on the motor heat, but this can be controlled by setting the current limit to the normal full load current, then even running very slowly will not cause overheating, except that the cooling fan will be less efficient and so the temperature needs to be watched. When the VFD measures the motor parameters at setup it will (should!) make suitable allowances for the supplied waveforms. The peak voltage is not a problem, the changes are made to the VFD output waveforms. There should be no problem running a 60Hz motor with a VFD at 50Hz speed, but this is not advisable without the VFD, there is a risk of excessive current and significant loss of efficiency. A VFD always supplies a square waveform at high frequency, it is the average current and effective frequency supplied that controls the motor speed. Special motors are sold for VFD operation, these have better magnetic material with less hysteresis loss, giving higher overall efficiency, but most other motors work just fine.

"A 3 phase induction motor can obviously run as star or delta" ............ If the motor is wound as such. If however a motor is designed for running in star then the frame size will be smaller and cheaper for the reduced heat loss. The rating plate should state the limitation.

Jaymack

This is becoming a very interesting discussion!

Jaymack - I'm not understanding - what is the difference in applying 380V to this motor with the windings in STAR or 220V to this same motor with the windings in DELTA?

Either way, the physical coils have the same voltage across them. Please enlighten - what design considerations would make this OK in STAR but not DELTA?

Just be clear - I'm not talking about STAR/DELTA starting.

Im talking about re-configuring into DELTA permanently and applying (sq root 3)* 380 = 220V to said winding.

There is no problem so long as the winding ends are available and the sense is clear - you do need to be a bit thoughtful about the sense of winding ends, as it is possible if inept to wire a motor in delta but with one winding reversed so that it expects two phases 60 degrees apart.

(as 120-180 is 60 ....)

And as others have said, you keep the voltage.frequency product down below the original.
Motors wired as star with the point of junction inaccessible  are another matter,, but not what you have here.

Mike

AdrianWint said:

What am I missing?

Hi Adrian. Have you queried this with the manufacturer?

Sorry, I had to ask.