Understanding Motor Name Plates

RyanM · 21 Mar 2012

Could someone help me with what the name plates actually mean on a motor.

The one I'm most familiar with is:
Star: 380-415V, 0.71A, 0.25kW

As all the motors I've seen are 3 phase and are wired in star. Like this, pretty standard I assume:

But, the names plates also have a single phase spec, like:
Delta: 220-240V, 1.23A, 025kW

So it would be wired like:

But, why is is 220-240V? As you still have 3 phases going to the motor.

I must be missing something totally obvious here, but please could someone explain?

Thanks a lot

vsynth · 21 Mar 2012

Hi, the Delta spec is 3 phase too, I have worked in some installations that have around 200V 3 phase.

You would wire the motor in Star if you have 415V 3 phase or Delta if you have 220V 3 phase.

Wiring it in Star when you only have a 220V supply obviously you will lose a lot of torque as the voltage across each individual winding will be too low.

RyanM · 21 Mar 2012

Thanks for the reply!

When would you have 3 x 220v supplies? Is the difference between 3 Phases, and 3 x 220v supplies the fact that the 3 phases would normally lag each other, where as 3 x 220v supplies would the same wave form?

I.e 3 phase wave:

Thanks

vsynth · 21 Mar 2012

Typically you get 220V 3 phase supplies on equipment that was not designed for the UK.

To use this equipment you then have a large transformer to bring the UK's 415V 3phase down to 220V 3phase.

The only difference is the voltage, the phase lag between each phase is identical to what you expect on 415V.

ricicle · 21 Mar 2012

There are some invertors that have a single phase input (230V) and a three phase output (230V). They were quite common in our factory.
They must be used in conjunction with a dual voltage motor connected in delta for 230V operation.

RyanM · 21 Mar 2012

Thanks for the reply, I think I'm understanding it better now

We do have some single phase input invertors which out 3-phase, and are wired in Delta. I guess this is the reason

Another potentially stupid question then:
If you measure across two phases of a 3 phase system, you would get 415v. If you measured between one phase of a 3 phase system and neutral, you would get 240v.
So, if you measured between two phases of a 220v 3 Phase system, would you get 220v or 110v?
What would you expect if you measured between one phase and neautral of a 220v 3 phase system?

Thanks a lot

ricicle · 21 Mar 2012

If you measure across two phases of a 220V three phase system guess what you will get - 220V !

The 220V three phase system would have to be from a star configured source to enable a neutral connection. The voltage between phase and neutral would be 220 / 1.73 = 127V approx.

RyanM · 21 Mar 2012

Thanks for you help again.

So I'm right it saying the 220v 3 Phase system is quite un-common in the UK?

I was under the impression (and wrong) that the 220-240v on the name plate mean't you would just use single phase, with a capacitor.

AdrianUK · 21 Mar 2012

For such a small motor as you are describing, you could indeed use a capacitor to get a phase shift and operate this on a 240V single phase supply. This trick doesnt work for anything bigger than about 0.5HP though. I've met a few small blower motors than can run 400 star, 230V delta or 230V single phase with a cap. I'll dig out the schematic tomorrow if I remember.

But, as others have said, the idea is to run 400V in star & 220V in delta. This is true for motors upto about 7.5kW, above this they are designed for 400V delta, 690V star.

Adrian

AdrianUK · 21 Mar 2012

For such a small motor as you are describing, you could indeed use a capacitor to get a phase shift and operate this on a 240V single phase supply. This trick doesnt work for anything bigger than about 0.5HP though. I've met a few small blower motors than can run 400 star, 230V delta or 230V single phase with a cap. I'll dig out the schematic tomorrow if I remember.

But, as others have said, the idea is to run 400V in star & 220V in delta. The 230V delta being intended for use with a 230V single phase to 230V three phase inverter drive. This is true for motors upto about 7.5kW, above this they are designed for 400V delta, 690V star.

Adrian

I don't know how I've managed to post this twice.... sorry!

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Understanding Motor Name Plates

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