wound rotors 1

[fsmyth]

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, 1425/1675 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 1000-1400%
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).

<als>

 

[petronila]

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

 

[electricpete]

I don't think it's syncronous. The nameplate speed is 1425/1675 rpm

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[fsmyth]

electricpete: I agree, since the slip calculates out to
look about right for this frame and general construction.

There are no values or mention of the field/armature
currents or voltages on the nameplate (otherwise, I
would experiment). As an addendum, one of the motors
had a few inches of AWG#8 wire left connected to the
slip rings. Not that that means a lot, probably.
<als>

 

[jraef]

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

 

[macmckim]

From my knowledge of Baldor - they do not mfg a WRM.

For single phase design they still mfg a repulsion induction motor for high torque applications. This type of motor has brushes and commutator (no slip rings) - up to 15 to 20HP maximum size.

As Fsmyth application is a mixer, I think the Baldor motor he has is just an induction motor, design D based on the 1675RPM (high slip/high torque). This would make sense for a mixer application. The voltages shown does not indicate any wound rotor voltage or amperage.

 

[jraef]

Then how do you explain the slip rings?

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[fsmyth]

Small update - I talked to a fellow at the place the
motor was made for; he did not recognize it, but said
he would look for the specs. Not optimistic here; the
original manufacturer was bought out by a larger concern.
It apparently was part of a _pump_ assembly, not a mixer.
It is a design D, class F.
at 220v 50Hz 52Amps Code E
at 380v 50Hz 30Amps Code E
at 208v 60Hz 55.4Amps Code F
at 240v 60Hz 48Amps Code F
with 12 leads (dual windings) and
2 (two) slip rings on the armature.
<als>

 

[powerjunx]

i never seen a WRIM made by BALDOR, when i was in field service for several years with that i agree to macmckim and since, a frame 286T series are usually TEFC SCIM.

in order to explain the slip ring, FSMYTH must detailed the motor construction and built..

..TELL US what is the internal contruction of the unit, the wire, the leads, etc all visual observation.

 

[Marke]

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

http://www.lmphotonics.com

 

[fsmyth]

Pretty sure about the slip rings. It is sorta hard
to confuse them with commutator bars.
<als>

 

[petronila]

Hello FSMITH,

I think this could help:

Older wound-rotor motors sometimes ground one rotor lead to the shaft.
That might be the case here. If so, it should be a conventional
wound-rotor motor but with one less slipring.

Regards

Petronila

 

[jraef]

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

 

[fsmyth]

I'll check it again, but I did check for shorted/grounded windings, and did not notice any continuity to the case.
Sounds like poor practice, unless the bearings are insulated.
And then there should be some method of contacting the shaft.
(There is not, on this motor; the slip rings are in an
enclosed end bell, with no shaft wiper).
<als>

 

[electricpete]

Well, I guess I'm not sure why there is an assumption that the rotor has to be a 3-phase circuit. It has to have the same number of poles as the stator field, but that can be accomplished with a single-phase multiple-pole winding on the rotor, right?

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[electricpete]

I realize that most wound rotor motors also have a 3-phase rotor but I wonder why it has to be that way.

I don't think there would be any problem with start torque. The forward rotating stator field would create a forward and reverse field in the stationary rotor. The reverse field cannot create any torque because it has not reverse rotating stator field to interact with (unlike single-phase motor). So only the forward rotating rotor field will interact with forward rotating stator field and no starting torque problems, even with rotor starionary.

I suspect there could be some torque oscillation.

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[mtrmkr]

FSMYTH - here you go. Look at the nameplate and find

FIG B
connect
10-11-12
4-5-6
Line 1-7
Line 2-8
Line 3-9

FIG C
connect
Line 1-12
Line 2-10
Line 3-11
7-4
8-5
9-6

FIG E
connect
Line
1
2
3
connect
7-4
8-5
9-6
10-11-12

interchange any two line leads to reverse rotation

FYI the OEM is still strong and kicking

 

[fsmyth]

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?

<als>

 

[petronila]

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

 

[Marke]

Hello fsmyth

Lets assume that we can use it as a single phse output rotor and you want to start it as a normal induction motor.
We need to determine the rotor characteristics so that we can calculate the value of resistance to connect to the rotor.

We need to find out what the open circuit rotor voltage is, and what the short circuit rotor current is. If there is no information on the nameplate, we will need to make measurements.

This can be done by connecting the stator as per usual for the line voltage you will use with the rotor stationary and the rotor winding disconnected. (open circuit) Measure the voltage on the rotor slip rings. (the rotor should not develop any torque!!)

Next connect the stator to a low voltage with the rotor locked and measure the short circuit rotor current. This will be approximately equal to the full voltage rotor short circuit current reduced by the voltage reduction ratio.
i.e. if the measurement is made with a stator voltage of 10% of line voltage, the measured rotor short circuit current will be about 10% of the full voltage short circuit current.

Best regards,

Mark Empson

http://www.lmphotonics.com