Reconnecting a star / delta motor.

electek · Jun 8, 2010

Hi All ,

Can anyone give me any advise on reconnecting a star / delta motor which was disconnected by someone else and the 6 wires were not labelled !

I understand the way star delta works and how it changes over e.t.c. e.t.c. but i've heard about in some cases motors running ok in star but tripping when swapping into delta cause they are incorrectley connected ??....

Also will the motor be rewound exactly as it 'came off' so that if the person had made a note of the connections it would be a case of simply reconnecting or is it possible that a rewind company could make any changes to the windings which would affect the running after reconnection.

I find the whole star / delta issue a bit confusing , can anyone explain the best way of ensuring all is correct ? Any help much appreciated.

Many Thanks

pmac10 · Jun 8, 2010

are the 6 wires coming out of the motor or have you got 6 wires to connect to u1,v1,w1,u2,v2,w2????

netblindpaul · Jun 8, 2010

electek,
If the motor has been rewound then it will not necessarily have been rewound exactly as previously.
My "pet" rewinder even though they are good are good at swapping the connections around.
All you can hope is they have the phase progression correct.
Are the motor terminals marked at all?
If so find U1, adjacent will be V1, adjacent to V1 will be W1, IF they have done it right!
Opposite U1 will be W2, opposite V1 will be U2, opposite W1 will be V2.
Now then, bell out the wires from the Y/D unit.
Take the LH most phase colour say Red or brown depending on the age of the wiring, this will be on T1 on the contactors, take the T1 of the line contactor to U1, the T2 of the line to V2, the T3 of the line to W1.
Right now the other contactor.
Take T1 to U2, T2 to V2, T3 to W2.
Try it and hope!
If this does not work shift the second contactor wires along one, T1 to V2, T2 to W2 and T3 to U2.
If that does not work same again.
If it is wrong at any point hope the TM O/L & CB's are good!!!
Only other way is to bell out the windings and power them up with d.c. to see which way to rotor kicks and you get the 1/2 from the rotor kicking the same way with d.c. for each pair, just pick one to start off with as U1 and just make the other u2 and go from there.
IF the motor goes backward, reverse the incoming phases its easier!

HTH, no guarantees, its a pain in the asre!!!!!!!

silva.foxx · Jun 9, 2010

See: http://www.electriciansforums.net/c...al/10495-star-terminal-block-arrangement.html

I provided a schematic for a star-delta connection. Bell out the circuit from the contactors making sure that one line from the line contactor, say R, passes thru the motor via U1 and U2 and thru the delta contactor to a different line, say S. Then S thru to T and T thru to R.

electek · Jun 9, 2010

Thanks for the advice guys.

Does it matter which motor coil you start with so long as the phases are 'one phase out' I.e if you pass through any motor coil ensuring it is returned by 'one phase out ' is that ok or do the motor coils have to be in sequence ?

Thanks for your help guys

netblindpaul · Jun 9, 2010

As long as you go through the windings in the correct & same direction you can start with any winding.

electek · Jun 10, 2010

Thanks for the reply's.

So if the motor terminals were not labelled at all and i identified with a test meter the three coils , put a phase onto the end of each coil and then returned the other end of each coil to the next phase along , this would be correct ?

Its not easy to explain what i'm trying to say but really what i am asking are the windings wound in order inside the motor or can i pick any of the three motor coils and so long as the end of each is returned to the following phase it will work ?

Thanks Chris

silva.foxx · Jun 10, 2010

U1, V1, W1 will be in-line on one side of the terminal block.
U2, V2, W2 will be in-line on the other side of the terminal block.

U1 should be opposite W2
V1 should be opposite U2
W1 should be opposite V2 as shown below;

U1 V1 W1
W2 U2 V2

U1 will be the start of one winding with U2 being the end.
V1 will be the start of an other winding, again V2 being the end.
W1 will be the start of the remaining winding, and you guessed it W2 being the end.

A reputable motor shop will have the windings in the right order, or orientation.

There is a simple procedure to check if the windings are in the same orienation. I can post it if you're really interested, but that may be going off on a tangent, typical for me!

electek · Jun 10, 2010

High Silva.foxx , Thanks for taking the time for your reply - its making sense now.

Would it be possible for you to post the other info you mentioned , i would be very interested in this.

Thanks again

silva.foxx · Jun 10, 2010

Ok... it's along these lines...

You'll need a working 3 phase AC induction motor, a 12v AC supply and a multimeter.

For the purpose of hands-on practice, remove the shorting links on the motor terminal box and attach a length of wire out of the motor from each of the terminals. Keep the wire the same colour to remove visual clues. Close the box lid so you can't see the terminals. You should now have six leads to look at.

Step 1. Identify the 3 pairs of windings using the multimeter. Mark the ends A,A, for the first pair, then B,B, then C,C

Step 2. Connect the 12v AC supply to the winding A,A. but do not turn on yet.

Step 3. Pick one end of the pair B,B, and connect it to one end of the pair C,C. With the remaining leads (one B and one C) connect to a multimeter set to volts AC.

Step 4. Turn on the supply. Check for a voltage reading on the multimeter. Now please note the following carefully...

The motor windings are referred to as "Starts" and "Finishes". If the connection between B and C is a "Start" joined to a "Finish", you will read a small voltage on the multimeter.
If no voltage is present, then the connection between B and C is a "Start" joined to a "Start" so swap one of the wires at the connection between B and C.

Step 5. Lets say you have successfully produced a voltage… should be around 4 volts. If you get to the stage whereby a voltage is produced, then mark the B lead at the junction with C as B1. Mark the C lead at the multimeter as C1. This will give you the relationship between the B and C windings.

Step 6. The above procedure needs to be repeated for the A,A winding....

Once all windings identified, open the terminal box and find if you have A1, B1 and C1 to the same side of the terminal block. If so... job's a good 'un!