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09-01-2008, 06:37 PM #1
Converting a three phase motor from star to delta configuration
I recently purchased an inverter to convert a three phase lathe to run on a single phase supply, the only snag I have run into, is converting the motor from a star to a delta configuration,There are only four terminals in the motor box , It is a Brook crompton dual voltage motor made in UK.
There are terminals A, B, C and N
The three brown power wires are attached to each of A ,B and C
A has a red wire going from it
B has a yellow wire
C has A blue wire
N has three wires connected - white, grey and brown,
How do I re wire to get the motor to run in the lower 220V delta configuration?
09-01-2008, 06:59 PM #2
I'm guessing the wires twisted together are the middle of the Y.
You'll have to sort out the individual windings with a meter. I'm guessing that the bunched wires are one end, and the other colors denote the other end of each winding. You'll have to unbunch the wires and connect them to the other terminals. Not really sure what order, or if it matters. You should be able to sort it out with an ohm meter.
09-01-2008, 09:20 PM #3
Do you know for a fact that it is a three phase and dual voltage? Say so on data tag?
09-02-2008, 05:04 AM #4
The lug on the far right (N) appears to have several motor leads under it?
You may want to check for continuity from each of those leads to the other motor leads. If you find 3 sets of coils this will hold the key to your answer.
Also, John has a good point. Is it a 220v motor? You might be able to get away with running a 480v motor Delta wired at 220v, but then again maybe not.
09-02-2008, 07:41 PM #5
The RGB is the mains in, each phase is going to one end of a winding, the other end of each winding is commoned on the N terminal.
So with a buzzer/meter etc. find out which terminal (1,2,3,) is connected to the commoned leads (W,Gy,Br).
The connections are then, one mains phase in to 1, other end of 1 goes to 2 and another live phase, the other end of 2 goes to 3 and another live phase, the other end of 3 goes to 1.
If the motor rotates in the wrong direction, reverse mains connections to 1 and 2.
09-03-2008, 07:11 PM #6
I've done the rewiring as Chuckey suggested, and it's sems to have worked.It is a dual voltage motor by the way.
09-03-2008, 07:46 PM #7
If I'm reading the various comments and speculations correctly, the motor is six wire, ∆/Y, and is wired as Y for high voltage and as ∆ for low voltage.
For the usual nine-wire motor, there is an internal Y-point, and low voltage is accomplished by making a Y out of the six lowest-numbered wires, and placing those in parallel with the remaining three wires (which implicitly includes the hidden Y-point) for low voltage.
This common motor has a 2:1 voltage ratio, such as 220/440, 230/460 or 240/480, but could be designed, tested and rated for 208-240/480 at no additional cost.
For a six-wire ∆/Y motor, which is the present case, the true voltage ratio is 1.732:1, not 2:1, but the motor can be designed, tested and rated for 2:1 with a small sacrifice in motor performance, or a small increase in motor cost.
True Y motors are becoming increasingly rare, and in my past lifetime as an EE at this Nation's largest municipal electric utility, I only saw true Y motors (that is, motors which actually used a neutral) at 4,160 volts, and those were very large motors, indeed.
In fact, for our 4,160 customers, they had to provide the transformer and switchgear as our standard services were any of: 120/240 ∆, 120/208 Y, 240 ∆ (rare), 277/480 Y, 480 ∆ (quite rare), 2,800 ∆ or 34,500 ∆, ONLY, which is why the customer had to provide the special transformer and switchgear.