3phase 3speed AC motor winding connections 1

[Andiri812]

Greetings all

I have a 380VAC 3phase, 3 speed motor electric motor with 9 leads emminating from the stator. Power rating +/- 1Hp, 2,4 & 8 poles listed on the nameplate with speeds of 2800, 1400 & 700rpm respectively. The motor has burnt and now there is much speculation in the shop as to how this type of motor is wound and connected. Does it have 2 or 3 windings? Some say 2: 1 winding for the 2pole, and another shared by the 4&8 poles, something to do with a midpoint connection and starring out certain terminals etc...???
The motor is from an automotive machine shop surface grinder dating back to at least the 70's.
Any experiences with this kind of motor or winding configuration would be helpful and interesting.

Cheers
Andrew

 

[ScottyUK]

Quite likely to have two windings in a Dahlander connection which would give a 2:1 ratio, so could be 2/4 poles or 4/8 poles. The third speed would be a dedicated winding.

I would look for a new motor and use a modern variable speed drive in preference to repairing an unusual motor. You can program many to give three pre-defined speeds in response to digital input signals, or you could use true variable speed to get any intermediate speed you wanted.


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If we learn from our mistakes I'm getting a great education!

 

[Andiri812]

Thanks Scotty, I'll search the Dahlander connection, haven't heard of it before but never too old to learn something new.
We have considered the VSD option on a new motor in terms of cost vs effort vs downtime on fixing the old. This unit has been rewound by our local motor rewind shop somewhere in the past but the chap who wound it retired many years ago, and don't reckon our new guys are up to speed with unusual winding configurations.
We were mostly curious about the connection but I reckon you've answered it.

Cheers

 

[ScusaMe]

ScottyUK

Something to think about :


Torque vs speed.

 

[ScottyUK]

ScusaMe,

Absolutely - the saving grace being that these old multi-speed motors are quite chunky, so you can usually get a much more powerful standard motor into the space vacated. By oversizing the motor you have sufficient torque at the lower speeds, while maintaining the top speed. You do need to consider the effect of potentially over-powering the machine at the higher speeds.

As an example I had one of these 3-speed motors on my old lathe which was nominally rated at 3HP. Even allowing for old horses being stronger than modern ones the replacement motor is 5.5kW, chosen partly on the basis of low speed torque and partly on the basis of mechanical compatibility. I wasn't going too far down the 'how to choose a replacement motor' route since it's reasonably well documented in numerous places and it wasn't the question which was asked, but feel free...


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If we learn from our mistakes I'm getting a great education!

 

[petronila]

Hello,
The motor is two independent windings, three speed motor: Single winding + dahlander winding.

To clarify the speeds ratios, could you provide the complete name plate? a picture? I think there we could find the answer, but wondering, why the repairshop don´t open the motor and take the winding schems? this action will clarify about the dahlander connection.

Regards

Carlos

 

[Motorwinder]

The ones I've wound were, the high speed 2pole was one winding. the mid and low speed, 4 and 8 pole were dahlander. Probably constant torque/variable horsepower.