Leads of a three phase induction wye-wye motor

[ePOWEReng]

Hello. Does anybody know how to find the correct 'pairs' of leads for a induction motor that is connected in a double wye configuration with the two wyes completely electrically disconnected. The two 'wye points' are not accessible, only the six phase leads. We are able to use an ohm meter to separate out the two wyes, but now the A phase, B-phase and C-phase needs to be "paired up" between to two wyes to form the right connections, does anybody know of a way to do this????? Thanks for any help you may have.

 

[SteveKW]

Using DC and a compass is one way if you remove the rotor.
If the motor is dual voltage and you have access to low voltage you can connect the motor high and do trial and error by "bump" testing. Of course, these suggestions are far more practical if its on a small motor and not connected to the load.

 

[electricpete]

Tough problem. Sounds like good suggestions from Steve.

Maybe if you can get a peak at the connection end that would also give some clue?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[edison123]

Interesting problem. One way could be to run the motor with each winding energised separately and looking whether the rotation directions are same in both the cases. If not, you switch two phases of one winding only.

* Homer Wisdom - "Operator, Give me the number for 911" *

 

[electricpete]

I'm not sure I understood edison's method. But it gave me another idea.... not sure if it'll work.

Let's say winding set 1 labeled x1 x2 x3 and winding set 2 labeled x4 x5 x6

Connect jumper x2-x5 (leave it in througout)

Energize the motor at no load using one set of wye windings x1 x2 x3.

This should create a syncronous rotating field which would induce in the second wye voltages which are in-phase with the corresponding phase of the first winding (correct?)

So with motor still running, (and observing suitable electrical safety precautions), attempt to check for in-phase or out of phase as follows: Measure voltage x1 to x4. If these are the same phase pairs, you will be adding voltages which are in-phase or 180 out and the resulting voltage x1 to x4 will go to 0 or will double. In that case you have found that pair x1/x2 is equal to pair x4/x5 (if voltage goes to zero) or is equal to pair x5/x4 (if voltage doubles).

If neither of the above occurs (not factor of 2 or 0 voltage) and you are comparing different phase pairs, I think you would see either no-change or sqrt(3) change (depending on polarity). In this case with x2-x5 still connectd, measure x1-x6. It darned well better change by 2 or 0 (else my theory is wrong). If it goes to 0, then x1/x2 is same pair as x6/x5. If it doubles, then x1/x2 is same pair as x5/x6.

Now you need to repeat considering a different pair. Since we have jumper already at x2-x5, consider pair x3/x2 in analogous manner to how we just considered x1/x2.

=======
Measure voltage x3 to x4. If these are the same phase pairs, you will be adding voltages which are in-phase or 180 out and the resulting voltage x3 to x4 will go to 0 or will double. In that case you have found that pair x3/x2 is equal to pair x4/x5 (if voltage goes to zero) or is equal to pair x5/x4 (if voltage doubles).

If neither of the above occurs (not factor of 2 or 0 voltage) and you are comparing different phase pairs, I think you would see either no-change or sqrt(3) change (depending on polarity). In this case with x2-x5 still connectd, measure x3-x6. It darned well better change by 2 or 0 (else my theory is wrong). If it goes to 0, then x3/x2 is same pair as x6/x5. If it doubles, then x3/x2 is same pair as x5/x6.

Well, it's late and that's a lot of stuff that just came out of my tiny tired brain. Better be careful. Two points that I would invite you guys to double check.
1 - Is my assumption that voltage in corresponding pairs will be in-phase or 180-out correct?
2 - If #1 is correct, have I described the method correctly or did I make a sloppy mistake?


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

I left out the detail... double compared to what?

The answer: Double compared to applied phase-phase voltage. Sqrt(3) compared to applied phase-phase voltage.


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

I look back and compare my method to edison and I see there is a difference in objective.

edison is trying to match rotation among the two pairs of winding.

I am trying to match phase pairs. I think this is correct. Each lead in one winding will have only one counterpart in the opposite winding. What is supposed to be phase 1 on the first wye (for example phase X1-X2) has to peak at the same time as what is supposed to be phase 2 on the second wye (for example X4-X5). Matching rotation doesn't guarantee this. Let's say the exact correct connection is that we connect to incoming power (L1 L2 L3) X1 X2 X3 from the first winding and X4 X5 X6 from the second winding. If we tried to connect X5 X6 X4 to L1 L2 L3 (along with X1 X2 X3), we still have the same rotation but I don't think it will work because X1-X2 now peaks at the same time as X5-X6 (rather than at same time as X4-X5 as designed).

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[edison123]

pete,

Come to think of it, I agree matching rotation doesn't guarantee phase matching. So scratch my idea.

If this is a wound rotor motor, then one can energise the rotor and measure the phase match by measuring the induced voltages between the two sets of winding as you say.

Most sure method would be to dismantle the motor and physically trace the leads.



* Homer Wisdom - "Operator, Give me the number for 911" *

 

[ccjersey]

How would it work to induce a voltage in the second wye by applying dc to the first one?

I am used to seeing 9 lead wye connected dual voltage motors, so 6 circuits 1-4,2-5,3-6,7-(10),8-(11),9-(12) (10,11,12 permanently connected wye)

So if you apply dc to lead 1 and lead 2 of one wye and measure with a volt meter on second wye to find the lead pair with most induced voltage with the correct polarity, that should be the parallel circuit 7-8 shouldn't it. Repeat for the other combinations 2-3 to find 8-9 and then 3-1 and 9-7. by the time you do the second set you should know if the first pair was 7-8 or 8-7.

I would try it if it were mine, and then bump it, but you're on you own,'cause I don't know if it will work.

 

[fsmyth]

Both Y neutrals inaccessable? Sounds odd, but if true, then
the hardest part of the job has been done already (finding
the polarity of the second set).
The following is completely speculative, since I have never
tried it, but if I had to do it, I believe that I would
run the motor on one set, then check voltages while moving
a single wire from the un-energized set from one incoming
phase to the next, through a suitable dropping resistor
(a light bulb or two, or three, enough to make up the same
value as the phase-phase voltage). Repeat for each wire on
the set being checked.
In other words, treat it as a Y-Y transformer.
<als>

 

[fsmyth]

See the thread "motor burn out". You may have the type of
motor that Waross is describing.
<als>

 

[electricpete]

"How would it work to induce a voltage in the second wye by applying dc to the first one? "

My suggestion was to apply 3-phase ac voltage to the first winding and run the motor no-load. That creates a syncronous rotating field which induces voltages in the other winding.


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[DickDV]

Sounds like this is one of those 12 lead part winding motors. Both independent windings are wye connected and one is for starting and both together are for running.

How to sort out the leads is beyond me. I have trouble enough when there is a good connection list!!!

Be careful not to confuse this 12 lead motor with a far more common 12 lead which is dual voltage. The connections are completely different.

 

[electricpete]

Good point Dick and others. We really need to understand the connection/purpose of these windings (at least I do). What leads you to believe it is a wye/wye? What does the nameplate say?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[petronila]

Hello Hold 6468,

I think some concepts expressed above are usefull.

I really think this is a PART WINDING MOTOR.In the U.S the winding leads are marked with 1,2 ,3 for the first half-winding and 7,8,9 for the second half.

With a meter find the two winding halfs, label the leads of the first half winding with 1,2 and 3. uncouple the motor, With a half rated voltage energize the first half winding NOTE THE ROTATION.turn off the motor and label each power wire with 1,2,3 in the same order of winding marks. (1 with 1, 2 with 2 and 3 with 3). Conect the power to the second winding half, the power wires marks 1,2,and 3 will remain, enrgize and note the rotation if is the same replace the power wire marks: 1 for 7, 2 for 8 and 3 for 9 and mark the winding leads in same order (7,8,9). If NOT turn off the motor and Interchange power wires 1 and 2, the motor will change the rotation direction and the leads of second half winding will be marked like: power wire 2 is lead winding 7, power wire 1 is lead winding 8 and power wire 3 is lead winding 9.

Now with all windings leads marked you can run the motor with a half rated voltage too, conect power Line 1 to 1-7, power Line2 to 2-8 and power Line3 to 3-9 energize and note the motor must run Ok with out strange noise and low current.

Regards

Petronila

 

[sreid]

Assuming that the motor is as hold6448 says (two independent wye's), I would visulize the windings as the primary an secondaries of a transformer. You could then excite two phases of one winding with, say, a 1 kHz sine wave and 'scope both the windings. The secondary windings that are in phase with the excitation and about the same amplitude will determine the matching phases.

 

[petronila]

Hold6468,

I think, with only six external leads is very hard to guarantee the motor is internal conected in stars. You could find deltas too. In one or other connection you are gonne find continuity between three windings leads.

Regards

Petronila

 

[aolalde]

As I understand the two neutral points are internal but without inter-connection, see drawing below.
That is a simple case and inductive kick will identify the corresponding leads. The two winding halves behave as transformers with the three phases interconnected in wye.
Identify the two halves with an ohm-meter by continuity. Separate two sets of three leads.
Select any set of three terminals and assign randomly T1, T2 and T3.
From the very same set, take one pair of marked leads randomly and apply a kick with 9 volts battery.
Check the induced voltage on the un-identified half, while the battery is “making”. One pair will show maximum induction (approximately double as compared to the other two pair combinations).
Maximum induction and positive polarity will correspond to the energized lead numbers.
Use an analogical type (needle) DC millivoltmeter.
For the example the positive terminal corresponds to T3 and the negative to T2

 

[waross]

It sure sounds like a part winding start motor.
Half voltage may be a good idea if half voltage is available, but a part winding start motor is designed to start and run on full voltage on the winding.
Connect one of the three leads of the second set to lead #1 of the first set of leads. Now you should have two leads unconnected. Measure the voltage from each of these to lead 2 and lead 3. If you read close to zero volts that is your connection.
If you can't find close to zero volts on both free leads, de-energise, move the lead that was connected to lead #1 to lead #2 and try again.

Put another way. label the groups #1,#2,#3, and #7,#8,#9.
Connect #1,#2, and #3 to the starter.
Connect #7 to #1 on the starter.
Energise.
Check the voltage from #8 to #2 and #3
Check the voltage from #9 to #2 and #3
The combination that results in close to zero volts is the Correct connection.
If you can't get zero volts, move #7 to #2 and retry. #8 and #9 will now be checked to #1 and #3.
If you still can't get zero volts, move #7 to #3 and try again.
This procedure is valid for both Wye and Delta part winding start motors.
Good luck.

 

[electricpete]

aolalde - why would we think that the pair with the max magnetic coupling is the same phase? The group physically adjacent to any pole-phase group will belong to a different group.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.