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.

 

[electricpete]

I knew I made a typo error 1.2 nanoseconds after i hit submit. I meant:

The group physically adjacent to any pole-phase group will belong to a different phase


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[waross]

Hey electricpete; You had it with
"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."
Your right on track here.

If you can find zero volts on the other two leads, that is the connection.
If you can't find zero volts, move your jumper to x3-x5 and try again.
There is one right connection and 5 wrong ones. This procedure finds the right one quite easily.

 

[aolalde]

Electricpete; I hope this answer yor question:
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.

1- Since the neutral is internally connected, exciting a pair of terminals like 1&2 or 2&3 or 3&1 will excite at least two interconnected pole-phase groups (the minimum for a 2 pole case with 6 pole-phase groups).
2- The exciting current will circulate through the “first lead connected” phase groups then trough the neutral connection will apply a reversed polarity current trough the “exit lead” phase connected groups.
3- The current pulse is the same in all pole phase groups since the circuit is series connected by the neutral point.
4- Applying the superposition theory, the flux produced by each pole-phase group matches the phase angle of those pole-phase groups with the same geometrical position.
5- Again the induction on the corresponding pole-phase groups will be the vectorial addition of the neutral connected phases.
6- Since rotor and stator lamination create a good magnetic conductor, all the coils will experience some induction but only the combination in phase will have the maximum induction and corresponding polarity.
7- That is very ease to be tested if you have any (correct) 9 leads standard motor, a small battery and a Simpson multimeter. Connect 4,5 &6 to make the second neutral. Check the induction in 7-8 , 8-9 & 9-7 when 1-2 are excited.

 

[waross]

When the motor is running on one set of windings, it acts as an induction generator. The rotating field will induce a voltage in the second winding that is close to line voltage and in the same phase relation.

 

[aolalde]

I agree with your post Waross; that is a way to find the phase sequence and matching leads. But my personal opinion is that the test with live voltage could be very hazardous, when it is made out of an appropriate test set.

 

[waross]

hi aolalde
I agree with you.
But connecting a part winding motor incorrectly is dangerous and expensive.
Having someone hold the moter down with his foot while you juggle 6 bare leads is not the way to go.
I would limit the hazard as much as I could.
Four leads would be connected to starter terminals, no problem.
I would tape up one of the other leads and tape my voltmeter lead to the last lead.
Another option is to connect all the leads to the starter, but make sure that the second contactor cannot close.
Remove and tape the coil wires.
The contactor is at this time being used as a safe point lo "Land" the second set of leads.
Then put a small jumper across ONE of the poles of the second contactor. Check the voltage across the other two poles. Check directly and cross check. If need be, shut down and change the connections. Repeat until successful.
BTW This is a good field test to verify the correct connection of any start winding motor before energising the first time.
It would have saved us some embarrasemnnt on a new installation once. There was some confussion between 6-7-8- and 7-8-9. Temporary field applied numbers on the leads from the controllers to the motors. Wires labelled 7-8-9 were misread as 6-7-8
One person connected the motors and another connected the controllers.
A mix of British equipment and North American equipment and numbering formats. Two new 40 HP motors went back to the distributor for repairs.

 

[ePOWEReng]

aolalde -- what your are saying makes sense, but after doing some testing with a similar motor the wyes seem to be out of phase from each other by 60 degrees so when applying a voltage on b-c on WYE1 the induced voltage is largest on a-c on WYE2.

 

[petronila]

Hello All,

I have some doubts about this question, I am agree is a part winding motor but I not sure about the two wyes connection, if you have 6 External leads how can we sure if the internal connections are not deltas??

And HOLDS Sayds "The two wyes are completely electrically disconnected" this minds the first half is not connected with the second half, in the case of the two halves will be connected in Wyes, the neutral points are not connected.

One alternative is using a surge test: arbitrarily number 1 set as 1-2-3, the other set as 7-8-9. Then parallel 1-7, 2-8, 3-9 and surge test it. Keep swapping the pair combinations until you get a good surge test. That will be the correct 1-7, 2-8, 3-9, If you don´t have a Surge tester
the other alternative is Use low voltage 3-phase AC and compare the current balance. The amperage will be unbalanced until you get the right combination.

The other method that could work is : dissamble the motor Apply DC to 2 leads of 1 circuit, use a compass to find the groups associated with that phase. Repeat with the other set of 3 leads, to find the pair of leads that complete the poles of that phase. Tag one set as 1-2, the other set
as 7-8. Now you know the remaining leads are 3 and 9, respectively.


Regards

Petronila.

 

[ePOWEReng]

We designed the have the engineering design drawing from the motor, so we know it is a Wye-Wye motor. It is a single-voltage, single-speed, three phase motor with six leads. The wyes do not show continuity.

 

[ePOWEReng]

Sorry I meant to say we have the engineering design drawings, so we know it is a wye-wye motor.

 

[ePOWEReng]

Thanks Petronila. We have done a surge test on this motor. That works good for the case that one lead is switched, but in the case that all leads are mis-paired the surge test passes the test when it should fail. i.e. connecting WYE1A-WYE2B, WYE1B-WYE2C, and WYE1C-WYE2A passes the surge test when it should fail.

 

[waross]

Hi petronila
Wye Vs. Delta. Good point, You can tell the difference with a resistance test. Check the resistance between T1 and T2. Check the resistance between T1 and T2-T3. The ratio will be different from Delta to Wye.
For a part winding start it doesn't matter if it's Wye or Delta.
Consider a 9 lead motor. the only connection between the 1-2-3, 4-5-6 group is at the starter. There can be no connection between the Y points because the 6-7-8 group has an internal Y connection that is not accesable. In the part winding start motor, the 4-5-6 Star connection is also internal and inaccessable.
A note on the compass method from some one who has actually used it;
On Wye,when you connect to T1, T2, it is difficult to tell with a compass which pole is winding 1 and which pole is winding 2, However, the place where there ISN'T a pole is probably winding 3.

 

[petronila]

HOLD did you try this??

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 marks the second winding half : power wire 1 is lead winding No. 7, Power wire 2 is lead wire No. 8 and power wire 3 is lead wire No. 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

 

[ePOWEReng]

Petronila,

Thanks for the help on this. This induction machine is operated as a generator in a hazardous/explosion environment. Additionally any tests that require getting to the inner parts of the motor are expensive as gas has to be purged first. What we are trying to find is a test that can be done using the six leads that are available at the junction box without applying a voltage near rated (6600 Volts) to the machine. I agree that your test would be a good solution in most induction motors. Any other ideas??

Thanks.

 

[waross]

Hi holds6448
Is the starter in a more benign location? You should have the same six leads at the starter as at the motor. I would do all testing at the starter.
I would modify my first suggestion a little.
Connect all six leads to the starter. Disconnect the coil on the second starter. Apply 208 V or 480 V three phase to the starter.
Depending on the physical arrangement of the windings, you may be able to identify the second set of leads by the transformer principal. If not, you will have to use a voltage high enough to spin the motor.
Do not energise the second set of windings, but jumper one pole of the second contactor and check the voltages across the two open poles on the second contactor. Look for the combination of connections that gives the lowest voltages across the open poles.
If you can use a voltage low enough that the test current is less than fulll load current you have a pretty good safety margin. Be aware that the current may be much more than normal with a wrong connection.
Keep us posted on your progress.
yours

 

[aolalde]

hold6448

You never mentioned that it was an Induction Generator and the line to line voltage being 6600 Volts. The test I gave to you applies an "inductive kick" with a low voltage battery and was intended for 230 or 460 volts motor.

The test you are doing is with steady AC.

You should apply 3 phases 60 HZ 220 or 440 volts to one wye system ( name it randomly T1,T2&T3).
To get voltage reference connect a jumper between T1 and watever terminal of the second system. Mesure the voltage between the other two remaining leads against T2 and T3, if a combination result in almost zero volts on each pair, you are done.
T7 is the one with the jumper to T1, T8 is the one with almost zero volts to T2 and the other is T9 (almost zero to T3).
If that selection does not work change the jumper from T1 to another lead of the second wye system until the condition above is reached and so on, remember that a jumper for reference is very important other way your two independent systems are floating randomly.

 

[waross]

Hi aolalde
Thanks for the support. I think we have the solution.

 

[vehazle]

Unfortunately it is not possible to apply any significant voltage/amperage to the generator. This is due to the fact that it is designed to run inside a can, submerged at very low temperatures. To get access to the 6 leads the machine must be drained and warmed-up. In this state any significant current will potentially damage the machine. Additionally this is being done a site that has rules that severely limit higher voltages.

It has been decided that the machine will be pulled out completely and taken to a workshop. One idea that came-up was using a phase rotation meter. The question with this is would it only confirm the the correct order of phases in each wye or can it also confirm the correct pairing between the wyes (a1-a2, etc)?

For reference, we tried the following test on a spare generator of the same design, but with known correct phase marking. I have been told that the orientation of the wyes are such that one wye is rotated 60degrees from the other. Essentially if you imagine a typed "Y", you have one upright and one inverted.

Apply a small voltage/amps to wye1 as indicated. Measure induced voltage on wye2.
Apply 25VAC/1.8amps to Wye1 a1-b1, induced voltage results: a2-b2=3.36V,b2-c2=1.71V,c2-a2=1.66V.

Apply 25VAC/2.4amps to Wye1 b1-c1, induced voltage results: a2-b2=2.00V,b2-c2=10.80V,c2-a2=8.80V.

Apply 25VAC/2.4amps to Wye1 c1-a1, induced voltage results: a2-b2=2.10V,b2-c2=8.75V,c2-a2=10.89V.

Then apply power on wye2 and measure on wye 1:
Apply 25VAC/1.8amps to Wye2 a2-b2, induced voltage results: a1-b1=3.36V,b1-c1=1.50V,c1-a1=1.70V.

Apply 25VAC/2.3amps to Wye2 b2-c2, induced voltage results: a1-b1=2.10V,b1-c1=10.90V,c1-a1=8.80V.

Apply 25VAC/2.3amps to Wye2 c2-a2, induced voltage results: a1-b1=2.10V,b1-c1=8.80V,c1-a1=10.90V.

The results were not quite what was predicted. It was thought that for each wye1 phase energized, there would be one wye2 phase voltage that would be 1.5-2 times higher than the others. Any ideas on why the results did not come out as expected? I do not know why the first phase powered, used less amperage as I was not present at the actual testing. I would imagine voltage magnitudes would be different, but the relation between the three wye2 phase voltages should be consistent.

Any help would be appreciated, especially regarding the use of the phase rotation meter.

Thanks

 

[waross]

Hi vehazle
Your results are a little surprising.
Re the inverted Wye. If this is correct you have a six phase machine which I doubt. My really old books show 6 and 12 phase connections for smoothing the ripple on rectifier feeds.
What is the power output or horse power?
Can you tell us how the machine is connected, how is it powered? Is it turned by a turbine and feed power into the line?
What type of controls and starters do you have?
Are all six leads connected to the line at once or are there two contactors, one for each winding.
If this is an induction generator phase rotation is important.
Readings are somewhat as I expected and somewhat not.
Remember, when you apply 3 phase to A1-B1-C1, there is a 120 deg. phase displacement between the three coils.
When you apply single phase to A1-B1, these two coil currents are in phase. You have two windings (A and B) in series with C tapped to the center point of the other two windings. Your Y is now a T. That is why the A-B voltges almost equal the B-C and C-A voltages.
I don't know the number of poles in the machine or the winding arrangement. Remember also that you're Making a transformer out of the motor when you do this test and you do not know the physical relationship of the coils exactly.
As for your test, When you energise A1-B1, you get the highest voltage across A2-B2, but you won't know which is which. However, the lead left over must be C2. Repeat the process.
Seeing as this is a generator, can you spin the unit to test it? After the leads are identified, try spinning the unit with 25 volts on A1-B1 and try your phase rotation meter on A2-B2-C2
If you can arrange 25 volts three phase, that may give you a good test that you can have confidence in to identify the leads. I wouold try the phase rotation meter on the spinning machine with single phase on the other winding. Otherwise the test may reflect the connection of the first winding rather than the direction of rotation.
yours

 

[vehazle]

Thanks for the input waross.

In answer to your questions:

-it is an induction machine: 3ph/1000kw/3300V/50hz. As for the connections the 2 wyes of the generator are connected to busbars where they are paired (generator side:line side), a1-a2:A, b1-b2:B, c1-c2:C. It is connected by a VFD to line and powered by a turbine.

As for the inverted wye the best way I can explain is to imagine the Y inverted Y where you have along the top points, a2,a1,c2 and along the bottom, b1,b2,c1. Now this is how it was described to me, I cannot verify it 100%.

I suspect that the winding arrangement is such that the a1,a2 windings are next to each other in the same quandrant, since I think they would oppose each other if they werent physically side by side.

Could you elaborate a bit more on the nature of the voltages that we actually measured? I am not quite sure what the relative voltages (not neccesarily magnitudes but relative)measured on wye2 should be expected for each application of voltage on wye1. Can they even be predicted without detailed knowledge of the winding locations?

Could you also elaborate a bit on the phase rotation meter? I am not quite clear on what exactly to do and look for.

Testing online with the VFD is not possible (ie motoring)nor testing with the process spinning the turbine. The machine will be in the workshop in a day or two. It will be possible to spin the rotor by hand when it is out.

Sorry for seeming somewhat lost, but electrical is obviously not my strong point.

Thanks in advance.