wound rotors 1 - Electric motors & generators engineering - Eng-Tips
Jun. 05, 2025
wound rotors 1 - Electric motors & generators engineering - Eng-Tips
I have the option to get another 20 HP Baldor -
and I really do want to learn more about these
motor types. Quoting a previous post:
" Just got a 20hp Baldor -
286TZ frame, / rpm, spec: 10P46W694,
stk no.: 39H314BAH, 208/240/60 and 220/380/50.
Talked to manufacturer - seems that this was
OEM'd to a mixer company, IIRC. Other than
that, no other specs.
I was hoping that someone had run across this
particular type, and could give me some pointers.
All of the documentation I can find refers to
3-phase rotor and stator windings - note that this
one has only 2 slip-rings, hence only one rotor
winding (more like a 3-phase alternator).
From what I have found, starting a wound-rotor
motor with the armature shorted has a -%
starting current (as opposed to 500-800% on a
"standard" squirrel-cage). Is this also true
for this (single-winding) type?
What I need is practical application info, such as
how much resistance to use (near as I can tell so
far, about 3x the rotor resistance), when to switch
it out ( again, NAICT, at over 80% speed), and what
the effects of more slip have on operation.
It appears to my small mind that this could be the
equivalent of delta-Y start, without the massive
switching transient, and (because of more slip)
be more responsive to load variations when used as
an RPC idler.
I can probably interpolate values from a 3-phase
rotor type, if I could just find them. I realize
that this is a small motor for the type - most of
the literature I have found refers to 500HP+, but
any hints are welcome."
Can anyone help, or at least provide some pointers?
I do not mind experimenting, but is is difficult for
me to set up (I have access to 3-phase, but have to
make arrangements in advance, and anything I do will
be in their way until done).
Hi fsmyth,
If you have an electric motor with wound rotor with 2 slip rings, this is a Synchronous Motor, This is a special kind and needs to be powered IN THE ROTOR with DC Voltage.Then You have to use Two diferent power sources : AC for Stator and DC for Rotor, for the last you need an electronic device capable to convert AC Voltage in DC Voltage,This voltage is called FIELD VOLTAGE, But it is not random dc voltage because is a fixed voltage. For this Small motor can be 50 or 60 Volts but is better you try to investigate the Name Plate Field Voltage to be absolute sure.
I hope this can help you.
Regards
PETRONILA
Just an opinion FWIW, but I'm not convinced it isn't a synchronous motor. I have never heard of a 3 phase WRIM with a 1 phase rotor. Why? What purpose would it serve, even in a custom job for a mixer OEM? Before we assume it is some bizzare bastard child, try to think of why they would need to do it. Having something that special would have cost someone a lot of money to design it and have Baldor make it as a special just for them.
On the other hand, a high speed synchronous application could be plausible for a mixer OEM in that they may have required a precise fixed speed that could be maintained at varying loads with some additional precision over an induction motor without the need for a VFD since the speed was not going to vary [inhale after long sentence].
If it is a synchronous, it most likely has an amotrisseur winding that will get it to 90% speed without the field being energized. Starting current for that winding would be similar to that of an induction motor, 500-600% FLA. If it is a WRIM, some amount of rotor resistance would be necessary for any reasonable operation.
So here is your test procedure. leave the slip ring circuit open. Apply 3 phase voltage to only the stator and if it does not accelerate, it was some sort of bizzare WRIM. If in accelerates to 80-90% speed, it is Synch. Don't run it for long in either case.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
Hello fsmyth
Are you sure that the motr has slip rings and not a comutator? There are some motors out there that only have two brushes but they are onto a commutator rather than slip rings. These are often able to be speed controlled by moving the postion of the brushes as in the Schrage motors. In this case, you feed AC voltage into the armature via the brushes. - just thought.
Otherwise, there is no reason that would totally preclude the use of a single winding rotor that I am aware of except that I would expect that the effective coupling would be reduced and the motor would probably demonstrate a higher slip under running conditions. It may have a less peaky torque curve or something?
Best regards,
Mark Empson
Petronila,
That's interesting, did not know that. Thanks for posting it, you get a purple star. Makes the rotor connection sort of like a corner grounded delta then doesn't it? It seems to me that would make for unbalanced rotor currents, but maybe if it was only intended to be used for starting, never running, it might make sense on an OEM special design like that.
I'll need to file that information away in the "almost completely useless information" section of my brain, which is unfortunately already very full (and no, I am not being sarcastic, I am genuinely impressed that you knew that). I will undoubtedly forget my home address one day, but if anyone ever says they have a 2 slip ring WRIM, I'll be able to tell them why!
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
Already looked at the nameplate
Your figures match except:
Figure E shows (near as I can tell; the numbers are dim):
Line
1
2
3
connect
4-7-12
5-8-10
6-9-11
Figure F (your figure E):
Line
1
2
3
connect
4-7
5-8
6-9
11-10-12
and Figure A (which makes no sense a'tall):
Line-1-4-7-10
Line-2-5-8-11
Line-3-6-9-12
Fig. C is for 220v/50Hz and 240v/60Hz
Fig. B is for 208v/60Hz
Fig. E is for 380v/50Hz
I did find a FIG. A on another (75 HP) motor that shows
Line-1-12-6-7
Line-2-10-4-8
Line-3-11-5-9
(labeled as low voltage delta run, using Fig. B as Y start)
which makes more sense.
And thanks, but this has nothing to do with my original
question: what to do with the ROTOR winding?
Hello fsmyth,
Did you know the motor´s history? all the time this motor was running for long time in one machine? or you only find this motor and you don´t know nothing of it.
When you tell "I'll check it again, but I did check for shorted/grounded windings, and did not notice any continuity to the case" I have a few questions: Did you test continuity between the rings?(Take a Ohms reading) did you see any wires came out from the winding and connecting to the rings?
Let me know what you find.
Regards
Petronila
and I really do want to learn more about these
motor types. Quoting a previous post:
" Just got a 20hp Baldor -
286TZ frame, / rpm, spec: 10P46W694,
stk no.: 39H314BAH, 208/240/60 and 220/380/50.
Talked to manufacturer - seems that this was
OEM'd to a mixer company, IIRC. Other than
that, no other specs.
I was hoping that someone had run across this
particular type, and could give me some pointers.
All of the documentation I can find refers to
3-phase rotor and stator windings - note that this
one has only 2 slip-rings, hence only one rotor
winding (more like a 3-phase alternator).
From what I have found, starting a wound-rotor
motor with the armature shorted has a -%
starting current (as opposed to 500-800% on a
"standard" squirrel-cage). Is this also true
for this (single-winding) type?
What I need is practical application info, such as
how much resistance to use (near as I can tell so
far, about 3x the rotor resistance), when to switch
it out ( again, NAICT, at over 80% speed), and what
the effects of more slip have on operation.
It appears to my small mind that this could be the
equivalent of delta-Y start, without the massive
switching transient, and (because of more slip)
be more responsive to load variations when used as
an RPC idler.
I can probably interpolate values from a 3-phase
rotor type, if I could just find them. I realize
that this is a small motor for the type - most of
the literature I have found refers to 500HP+, but
any hints are welcome."
Can anyone help, or at least provide some pointers?
I do not mind experimenting, but is is difficult for
me to set up (I have access to 3-phase, but have to
make arrangements in advance, and anything I do will
be in their way until done).
Hi fsmyth,
If you have an electric motor with wound rotor with 2 slip rings, this is a Synchronous Motor, This is a special kind and needs to be powered IN THE ROTOR with DC Voltage.Then You have to use Two diferent power sources : AC for Stator and DC for Rotor, for the last you need an electronic device capable to convert AC Voltage in DC Voltage,This voltage is called FIELD VOLTAGE, But it is not random dc voltage because is a fixed voltage. For this Small motor can be 50 or 60 Volts but is better you try to investigate the Name Plate Field Voltage to be absolute sure.
I hope this can help you.
Regards
PETRONILA
Just an opinion FWIW, but I'm not convinced it isn't a synchronous motor. I have never heard of a 3 phase WRIM with a 1 phase rotor. Why? What purpose would it serve, even in a custom job for a mixer OEM? Before we assume it is some bizzare bastard child, try to think of why they would need to do it. Having something that special would have cost someone a lot of money to design it and have Baldor make it as a special just for them.
On the other hand, a high speed synchronous application could be plausible for a mixer OEM in that they may have required a precise fixed speed that could be maintained at varying loads with some additional precision over an induction motor without the need for a VFD since the speed was not going to vary [inhale after long sentence].
If it is a synchronous, it most likely has an amotrisseur winding that will get it to 90% speed without the field being energized. Starting current for that winding would be similar to that of an induction motor, 500-600% FLA. If it is a WRIM, some amount of rotor resistance would be necessary for any reasonable operation.
So here is your test procedure. leave the slip ring circuit open. Apply 3 phase voltage to only the stator and if it does not accelerate, it was some sort of bizzare WRIM. If in accelerates to 80-90% speed, it is Synch. Don't run it for long in either case.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
Hello fsmyth
Are you sure that the motr has slip rings and not a comutator? There are some motors out there that only have two brushes but they are onto a commutator rather than slip rings. These are often able to be speed controlled by moving the postion of the brushes as in the Schrage motors. In this case, you feed AC voltage into the armature via the brushes. - just thought.
Otherwise, there is no reason that would totally preclude the use of a single winding rotor that I am aware of except that I would expect that the effective coupling would be reduced and the motor would probably demonstrate a higher slip under running conditions. It may have a less peaky torque curve or something?
Best regards,
Mark Empson
Petronila,
That's interesting, did not know that. Thanks for posting it, you get a purple star. Makes the rotor connection sort of like a corner grounded delta then doesn't it? It seems to me that would make for unbalanced rotor currents, but maybe if it was only intended to be used for starting, never running, it might make sense on an OEM special design like that.
I'll need to file that information away in the "almost completely useless information" section of my brain, which is unfortunately already very full (and no, I am not being sarcastic, I am genuinely impressed that you knew that). I will undoubtedly forget my home address one day, but if anyone ever says they have a 2 slip ring WRIM, I'll be able to tell them why!
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla
Already looked at the nameplate
Your figures match except:
Figure E shows (near as I can tell; the numbers are dim):
Line
1
2
3
connect
4-7-12
5-8-10
6-9-11
Figure F (your figure E):
Line
1
2
3
connect
4-7
5-8
6-9
11-10-12
and Figure A (which makes no sense a'tall):
Line-1-4-7-10
Line-2-5-8-11
Line-3-6-9-12
Fig. C is for 220v/50Hz and 240v/60Hz
Fig. B is for 208v/60Hz
Fig. E is for 380v/50Hz
I did find a FIG. A on another (75 HP) motor that shows
Line-1-12-6-7
Line-2-10-4-8
Line-3-11-5-9
(labeled as low voltage delta run, using Fig. B as Y start)
which makes more sense.
And thanks, but this has nothing to do with my original
question: what to do with the ROTOR winding?
Hello fsmyth,
Did you know the motor´s history? all the time this motor was running for long time in one machine? or you only find this motor and you don´t know nothing of it.
When you tell "I'll check it again, but I did check for shorted/grounded windings, and did not notice any continuity to the case" I have a few questions: Did you test continuity between the rings?(Take a Ohms reading) did you see any wires came out from the winding and connecting to the rings?
Let me know what you find.
Regards
Petronila
Inductive Imbalance in a Wound Rotor Motor - CBM CONNECT®
Inductive Imbalance in a Wound Rotor Motor
Wound rotor motors are used for a variety of applications where high torque is needed at low speeds, such as conveyors, cranes, shredders, and more. Standing next to a hp wound rotor motor driving a shredder at a steel-recycling plant while an old car with a 454 big block engine gets shredded is something we should all experience.
If you want to learn more, please visit our website.
Testing wound rotor motors can be tricky depending on what and where you are testing. Different from a squirrel cage motor, a wound rotor motor has windings on the stator and rotor. This makes it similar to a transformer in that changes in the secondary (rotor) circuit can cause large influences to measurements taken on the primary (stator) windings.
Goto CHANGLI ELECTRIC MOTOR to know more.
For baseline or troubleshooting a wound rotor motor, we recommend testing the rotor circuit, resistor bank, and stator windings separately. If a large inductive imbalance is seen on the stator, remember that it could be caused by something changing in the rotor or resistor bank circuits.
Contamination between slip rings connected to the rotor circuit may create a false symptom on the stator winding. When the brushes are lifted, they are more likely to touch each other, possibly shorting out a phase of the resistor bank, which will also have a large influence on the stator winding, leading an analyst to suspect stator winding defects. Normally a wound rotor motor in the warehouse will have the brushes lifted, so look before you test.