3phase 3speed AC motor winding connections
3phase 3speed AC motor winding connections
(OP)
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
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





RE: 3phase 3speed AC motor winding connections
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!
RE: 3phase 3speed AC motor winding connections
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
RE: 3phase 3speed AC motor winding connections
Something to think about :
Torque vs speed.
RE: 3phase 3speed AC motor winding connections
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
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If we learn from our mistakes I'm getting a great education!
RE: 3phase 3speed AC motor winding connections
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
RE: 3phase 3speed AC motor winding connections