Leads of a three phase induction wye-wye motor
Leads of a three phase induction wye-wye motor
(OP)
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.





RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
Maybe if you can get a peak at the connection end that would also give some clue?
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RE: Leads of a three phase induction wye-wye motor
* Homer Wisdom - "Operator, Give me the number for 911" *
RE: Leads of a three phase induction wye-wye motor
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?
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RE: Leads of a three phase induction wye-wye motor
The answer: Double compared to applied phase-phase voltage. Sqrt(3) compared to applied phase-phase voltage.
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RE: Leads of a three phase induction wye-wye motor
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).
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RE: Leads of a three phase induction wye-wye motor
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" *
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
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>
RE: Leads of a three phase induction wye-wye motor
motor that Waross is describing.
<als>
RE: Leads of a three phase induction wye-wye motor
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.
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RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
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RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye 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.
RE: Leads of a three phase induction wye-wye motor
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RE: Leads of a three phase induction wye-wye motor
The group physically adjacent to any pole-phase group will belong to a different phase
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RE: Leads of a three phase induction wye-wye motor
"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.
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
Thanks for the support. I think we have the solution.
RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye motor
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
RE: Leads of a three phase induction wye-wye motor
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.
RE: Leads of a three phase induction wye-wye motor
First the phase rotation meter. The ones that I have used are typically quite small and rugged. There are three coloured leads, and two lights. One old model has two small (1/2" Dia.) windows with a movable target thaat apears in one or the other window. You connect the three leads to the circuit under test and one or the other light illuminates to indicate A-B-C or C-B-A.
Inverted Y, This does not seem compatible with connecting A1-A2, B1-B2, C1-C2, I suspect a misunderstanding or a typo.
Maybe others will have some ideas.
There is another test meter that is often found in company with the phase rotation meter. The two are often used together when starting motors for the first time, when the direction of rotation is critical, or a large number of motors are involved.
This is the motor rotation meter, or indicator. It has three leads that are connected to the motor leads. The motor under test is turned by hand and the indicator shows the correct connections, A-B-C or B-C-A to achieve that rotation.
Voltages. If you can arrange three phase 25 volt testing in the shop, you MAY get better results.
Single phase testing with 25 volts. Imagine a Tee that is labled A1, B1 across the top, and C1 on the bottom. That is the electrical connection you have with a single phase voltage applied across A1-B1.
As you can see, C1 is tied to the center point. Electrically, the C phase winding is 90 deg out of phase with the A-B connection, however, with a three phase rotating machine connected as a single phase transformer, I honestly don't know what to expect.
However your readings seem to indicate that the physical position is such that virtually no voltage is being induced in the "C" winding, and it is reading the voltage at the center point of the A-B pair. However, I don't quite trust the readings.
I would have more confidence in a test with three phase 25 volts in the shop. If you can apply enough voltage in the shop that the machine rotates, I would trust the tests even more. If you can arrange a pony motor to spin the generator in the shop you can probably get a good test.
Let us know how the testing progresses.
yours
RE: Leads of a three phase induction wye-wye motor
I think if you can´t find the problem with all above explanations, and with a surge test, the better way is dissambling the machine and testing the stator winding in a shop, i think the winding could be damage.
Regards
Petronila.
RE: Leads of a three phase induction wye-wye motor
RE: Leads of a three phase induction wye-wye motor
The voltage induced in the unconnected winding is either adding or subtracting from the voltages that would be seen on the unconnected winding if no voltage was induced in it.
Still, the unconnected winding is the one that is identified at each step in the test.
RE: Leads of a three phase induction wye-wye motor
As it turns out the test using a single phase AC voltage on wye1 and measuring the induced voltages on wye2 worked as it was intended. The problem was that the spare generator that we found the strange readings was not exactly the same design as the generator in question.
The generator we were having problems with was manufactured within the last few years by another manufacturer than the spare generator which was built about 8 years ago. The newer, problematic generator was connected in a weaved or laced (not sure of the correct terminology) pattern whereas the older, spare generator was built in a lapped (again not sure of the correct terminology).
I will attempt to clarify in this text format.
For the problem generator in the weaved/laced configuration, imagine as I described above as an upright Y and and inverted Y. From left to right at the top you have a2,c1,b2 and along the bottom b1,c2,a1.
For the older, spare generator in the lapped configuration, imagine something like "3E" where from top to bottom on the "3" you have a1,b1,c1 and on the "E" you have c2,b2,a2.
In either case the corresponding phases on each wye are 180deg apart but the directions are opposite from eachother when looking down the axis of the generator, ie a1 is away from you and a2 is towards you. This gives you a North pole and a south pole on opposite sides.
If you care to take the time to draw these two scenarios out and sketch the wye phasing check procedure you will see that the laced/weave configuration is quite symmetrical whereas the lapped configuration is only symmetrical for one combination. This explains why we obtained the strange readings on the spare generator.
The wye phasing check procedure was developed with the manufacturer of the newer generator with the laced/weaved pattern and we did not know at the time that there could be another method for the coil connections so we were suprised by the results from the spare generator in the lapped configuration. The key to figuring out that there were two different constructions was that we have yet another generator at this site that was originally built about 8 years ago by the first manufacturer. We performed the wye phasing check on this generator and obtain the symmetric results that were predicted. This initially really confused us until we found out that this third generator was sent back to the second generator manufacturer for rewinding. During this rewind the second manufacturer changed the coil connections from the lapped to the laced/weave configuration. After some discussions with the engineers at both manufacturers we determined the source of the discrepancy between predicted results and the those obtained on the spare generator.
Ultimately we performed the check on the problem generator and determined that the leads were indeed marked incorrectly and hence were connected incorrectly which were the source of the problem.
I wanted to post a follow-up in case it could help someone else in the future and to thank everyone here for their suggestions and help. I also want to thank Hold6448 and his team for helping to figure this problem out.