1. Introduction

In today&#;s world, special focus is on the production of electric vehicles (EV) and hybrid electric vehicles (HEV) to extenuate the reasons of environmental pollution. High efficiency and torque density are the traits due to which permanent magnet (PM) motors are traditionally used for these applications. However, PM motors for traction applications exhibit lower efficiency at low load conditions. Additionally, the substantial increase in the cost of PM materials creates a need to find an alternative for traction applications such as EVs. Hence, many machines operating on the magnet-less principle are widely considered as another possible option.

Link to ZCL

In References [ 1 2 ], the comparative analysis of the interior permanent magnet synchronous machine (IPMSM) and induction machine (IM) is performed for the HEV application driven by IPMSM of the Toyota Prius. In Reference [ 3 ], a switched reluctance machine (SRM) is compared with the Toyota Prius machine for HEV applications. In Reference [ 4 ], a SRM is designed to achieve competitive torque and efficiency compared to the Toyota Prius IMPSM. In Reference [ 5 ], the comparison is performed between IM, IPMSM and surface mounted permanent magnet synchronous machines (SPMSM). For the fair comparison, machine dimensions, inverter size, and the vehicle specifications were kept the same. In Reference [ 6 ], the comparison between the ferrite PM-assisted synchronous reluctance machine and the IPMSM was performed for EV applications. In this research, the feasibility of replacing the IPMSM with a ferrite PM-assisted synchronous reluctance machine was investigated based on the Toyota Prius system. However, WRSMs are not yet seriously compared with the PM machines for traction application. In this paper, WRSM was designed and analyzed to show the suitability of the conventional WRSM for traction applications.

In Reference [ 7 ], a conventional WRSM was studied and analyzed to compare its performance with a PMSM. When the performance was analyzed, it was observed that PMSM cou;d be replaced as an alternative with the conventional WRSM in EV applications.

We can infer that the main trait of WRSM is that it can adjust the excitation current without drawing reactive power. With this ability, even if the voltage source of the inverter is unable to adjust the torque and power factor, WRSM can achieve this feat. This ability is not present in PM machines because the permanent magnets exhibit the properties of a constant source of excitation and their excitation cannot be controlled. For traction applications, this lack of excitation control creates problems in the design of PM machines.

The efficiency of the WRSM is marginally less than the PM machines because of the additional losses in the field winding of WRSM. Additionally, the per unit field winding resistance is only 1/4 to 1/10 than that of the resistance of phase winding of the stator, therefore, the efficiency of the two machines differs by only a few percent at rated load conditions. However, WRSM has the ability to adjust the field excitation, which allows the WRSM an added advantage in optimizing the efficiency of the WRSM above and below the rated load conditions. In addition, there are three control variables including the direct-axis current (

id

), quadrature-axis current (

iq

), and the field current (

if

) in WRSM, which allow more optimization possibilities compared to the PM machines, which have only two control variables;

id

and

iq

. The ability of field excitation control and flexible control with three variables makes WRSM more suitable for numerous applications, among which the most significant could be the EV applications

9,12,13,14,15,16,17,18,19,20,21,22,23,

However, in the conventional WRSM, the excitation is provided to the field winding of the rotor for the generation of the rotor flux through the external dc supply using the brushes and slip-rings assembly. Because of this issue, the WRSM was not considered as a suitable candidate for EV applications. However, it is important to note that much research based on brushless topologies for WRSM are in progress to overcome this problem. One of the approaches to overcome this problem is to use a rotary transformer operating at high frequency [ 8 10 ]. Other research towards the brushless excitation is to utilize the synchronous machine as a device for self-excitation and torque production [ 11 24 ].

In Reference [ 11 ], the high winding space harmonics are utilized to excite the rotor field winding. A tooth concentrated winding is placed on the stator and the rotor, and it does not require any additional auxiliary winding for the brushless operation. In Reference [ 12 ], a PM-less synchronous machine has been studied. In this topology, space harmonics power was utilized for the field magnetization instead of permanent magnets.

14,15,16,17,18,15,16,17,18,

In References [ 13 19 ], the brushless operation of WRSMs was accomplished by generating and employing the fundamental and sub-harmonic components in the MMF for the stator. For the generation of the sub-harmonic component, winding at the stator was specially arranged in these brushless topologies. In Reference [ 13 ], two parallel distributed windings with two layers were placed at the periphery of the stator and each winding was supplied using a separate three-phase inverter. In this topology, two inverters were used which is the core issue of this brushless topology, and it results in high size and cost. To overcome this issue, single-inverter fed sub-harmonically excited brushless topologies were presented in [ 14 19 ].

21,22,

In References [ 20 23 ], for the brushless operation of WRSMs, a third-harmonic component was utilized in the magneto-motive force for the stator. In order to carry out brushless operations of WRSM, the third harmonic component of MMF for the stator of the spatial domain was utilized in [ 20 ]. In this brushless method, two inverters supplied the current into the open winding, which is three phase and placed on the stator. The components of the current supplied by the first and second inverter are fundamental and third harmonic, respectively. The third harmonic component of MMF induces the voltage in the harmonic winding. The rectification of the induced voltage in harmonic winding is performed, and then subsequently, the dc current is fed to the field winding of the rotor for the brushless excitation.

In Reference [ 21 ], for the excitation, the field winding of the rotor, a zero-sequence current, albeit controllable, is generated for the excitation of the rotor field winding by connecting in parallel the thyristor switches and three-phase stator winding which helps when switching during the positive as well as the negative half cycles. The voltage in the harmonic winding is induced using the third harmonic component which is produced from the zero-sequence current, and then the dc current is given to the field winding after the rectification of the said component. From these research, it is obvious that the solution towards the brushless excitation system is very promising. In the aforementioned, third-harmonically excited machines, third harmonic is generated and then utilized for the brushless operation.

In Reference [ 22 ], the why-delta configuration of the stator winding is utilized to operate the machine on a brushless principle, which was produced due to the delta coil set in the stator winding. In Reference [ 23 ], a PM-less synchronous machine was studied. In this topology, a separate inverter was used to generate the third harmonic through time-division multiplexing technique, which was later used for the brushless operation of the WRSM. All the aforementioned brushless WRSMs have the issue of a low starting torque, which makes them unsuitable for practical applications.

In this paper we present the suitability of the conventional WRSM for EV applications. Section 2 describes the WRSM design and 2-D finite element analysis (FEA) of the basic model of the WRSM. Section 3 presents the rotor pole shape optimization for the improvement of the torque and the reduction in the torque ripple for the machine. Moreover, based on the performance, the comparative analysis is performed for the optimal model of WRSM and basic model of WRSM. In Section 4 , the wide speed range operation of the optimal model based WRSM is analyzed. The conclusion of this work is then presented in Section 5

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wound rotors

wound rotors

fsmyth

(Electrical)

(OP)

26 Jul 05 09:17

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).

<als>

Replies continue below

Recommended for you

RE: wound rotors

petronila

(Electrical)

1 Aug 05 19:13

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  

RE: wound rotors

electricpete

(Electrical)

1 Aug 05 20:20

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

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RE: wound rotors

fsmyth

(Electrical)

(OP)

2 Aug 05 06:17

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>

RE: wound rotors

jraef

(Electrical)

2 Aug 05 14:35

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.

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

RE: wound rotors

macmckim

(Electrical)

3 Aug 05 23:41

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 RPM (high slip/high torque). This would make sense for a mixer application.  The voltages shown does not indicate any wound rotor voltage or amperage.

RE: wound rotors

jraef

(Electrical)

4 Aug 05 02:55

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

RE: wound rotors

fsmyth

(Electrical)

(OP)

4 Aug 05 08:56

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>

RE: wound rotors

powerjunx

(Electrical)

4 Aug 05 08:59

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.

RE: wound rotors

Marke

(Electrical)

4 Aug 05 15:29

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,

Hello fsmythAre 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

RE: wound rotors

fsmyth

(Electrical)

(OP)

4 Aug 05 18:22

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

RE: wound rotors

petronila

(Electrical)

10 Aug 05 16:56

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

If you want to learn more, please visit our website Synchronous Motor for Ball Mill.

RE: wound rotors

jraef

(Electrical)

10 Aug 05 20:13
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!

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

RE: wound rotors

fsmyth

(Electrical)

(OP)

12 Aug 05 09:30

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>

RE: wound rotors

electricpete

(Electrical)

13 Aug 05 14:56

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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RE: wound rotors

electricpete

(Electrical)

13 Aug 05 17:27

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.

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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RE: wound rotors

mtrmkr

(Mechanical)

24 Aug 05 10:48

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

RE: wound rotors

fsmyth

(Electrical)

(OP)

24 Aug 05 11:37

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>

RE: wound rotors

petronila

(Electrical)

30 Aug 05 12:58

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   
  

RE: wound rotors

Marke

(Electrical)

30 Aug 05 15:00

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,

Hello fsmythLets 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

RE: wound rotors

shagooo

(Electrical)

24 Sep 05 09:17

Just a quick addition to this thread, if it's still going.  Years back I encountered wound rotor motors with the rotor being connected to a series of large wattage resistors.  There were also from one to four contactors across banks of these resistors that when energized, would short out the resistors.  This was used to control the speed of large cranes and hoists.

Just my 2 cents

RE: wound rotors

electricpete

(Electrical)

24 Sep 05 11:36

Shagoo - How many slip rings?

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RE: wound rotors

CJCPE

(Electrical)

24 Sep 05 14:01

I wonder if it is possible that a 3-phase rotor winding is connected to a 3-phase bridge rectifier mounted on the rotor and feeding DC to the slip rings. The DC from the slip rings could then be connected to a chopper and resistor for speed control or to a regenerative SCR bridge for speed control with slip energy recovery.

It is also possible that the motor is mounted to the housing of an eddy current clutch and the slip rings are for energizing the clutch field. The clutch assembly would be a lot larger than a regular end bell, but a lot of people don't realize that they are looking at two machines coupled together when they see an eddy current drive.

Both of these types of equipment were often used with pumps as a means of flow control before adjustable frequency drives took over that market.

RE: wound rotors

fsmyth

(Electrical)

(OP)

26 Sep 05 09:42

Thanks, CJ.
From the bit that I know and have read lately about
motors, I see a couple of possibilities:
a) the rotor is fed some value of D.C. in order to
generate a constant rotor field (like a D.C. motor),
or b) a resistor is placed across the rotor winding
while starting, and shorted when up to speed, and
c) resistors are used to control slip and thus also
possibly the efficiency of the motor when running.
I lean heavier to the b) option, since there is no
information on the nameplate refering to the rotor.

If the rings go to a brake, the winding(s) are
internal to the motor housing (which I doubt, since
the housing appears to be the proper size for a
motor of this rating - a 286T).
 The end bell is only large enough to contain the
brush holders (if you are referring to the small added
tin globe-like enclosure added to one end of the
shaft). Both ends of the motor housing, if that is
what you are referring to as end bells, are identical.

I am beginning to be more interested in these motors
as generators, if only I could find out a bit more on
the normal operating modes and ratings.

<als>

 

RE: wound rotors

jraef

(Electrical)

26 Sep 05 16:43

Wound Rotor Induction Motors are a completely diferent animal. The only similarity is that the both have slip rings. This is what Pertonila was refereing to way back on Aug. 1. If I'm not mistaken, applying DC to the rotor of a WRIM makes it into a Brake!

I think perhaps there is some confusion here between Wound Rotor Induction Motors and Sychronous Motors. Both have slip rings, but in a Sychronous motor they are used to apply DC to the rotor to change the field strength. This has nothing to do with speed control, it is used to change the power factor of the motor, and can even make the motor run at a leading power factor in order to correct a facility's PF from other induction motors on line at the same time. Synchronous motors are also more easilly capable of being used as generators since the field is separately excited, unlike induction motors, including WR induction motors.Wound Rotor Induction Motors are a completely diferent animal. The only similarity is that the both have slip rings. This is what Pertonila was refereing to way back on Aug. 1. If I'm not mistaken, applying DC to the rotor of a WRIM makes it into a Brake!

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

edison123 (Electrical) 26 Sep 05 21:31

Applying DC to the WRIM rotor (after it has reached full speed), will make it a synchronous motor. These are special motors called as synchronous-induction motor, which start as induction motors and run as synchs.

Applying DC to the stator makes it a brake - Dynamic braking.

jraef,Applying DC to the WRIM rotor (after it has reached full speed), will make it a synchronous motor. These are special motors called as synchronous-induction motor, which start as induction motors and run as synchs.Applying DC to the stator makes it a brake - Dynamic braking.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

davidbeach (Electrical) 27 Sep 05 01:05

Quote (edison123):

Applying DC to the stator makes it a brake - Dynamic braking.

I beg to disagree.  Not about the brake part of it, but about the dynamic braking part.  Dynamic braking is when a motor is driven by the load (becoming a generator) and the output power is dumped into a resistor (or other load) in a controlled manner, thus extracting energy from the load.  If the power produced in this manner is pushed back into the power system instead of being dumped, it is regenerative braking.

There comes a point at which the shaft is turning too slowly for effective dynamic or regenerative braking, at that point the DC to the stator would work better as a brake.  What you get when you apply DC to the stator of a synchronous motor is a motor with a synchronous speed of 0.

I beg to disagree. Not about the brake part of it, but about the dynamic braking part. Dynamic braking is when a motor is driven by the load (becoming a generator) and the output power is dumped into a resistor (or other load) in a controlled manner, thus extracting energy from the load. If the power produced in this manner is pushed back into the power system instead of being dumped, it is regenerative braking.There comes a point at which the shaft is turning too slowly for effective dynamic or regenerative braking, at that point the DC to the stator would work better as a brake. What you get when you apply DC to the stator of a synchronous motor is a motor with a synchronous speed of 0.

RE: wound rotors

edison123 (Electrical) 27 Sep 05 03:14

regenerative braking is different from dynamic braking.

regenerative braking involves hypersynchrounous speed (negative slip) and will be ineffective when the motor reaches synch speed.

Dynamic braking involves applying DC to the stator immediately after disconnecting the 3 phase supply. With slipring motors, resistances can be introduced in the rotor winding ckt to get better braking upto standstill.

davidbeach,regenerative braking is different from dynamic braking.regenerative braking involves hypersynchrounous speed (negative slip) and will be ineffective when the motor reaches synch speed.Dynamic braking involves applying DC to the stator immediately after disconnecting the 3 phase supply. With slipring motors, resistances can be introduced in the rotor winding ckt to get better braking upto standstill.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

jraef (Electrical) 27 Sep 05 04:05

Quote:

Applying DC to the WRIM rotor (after it has reached full speed), will make it a synchronous motor. These are special motors called as synchronous-induction motor, which start as induction motors and run as synchs.

So what is the difference between this and a Synchronous motor which uses it's amortisseur winding (induction machine) to get it up to pull-in speed? Semantics? Being that up until reading this thread I had never heard of a WRIM with single phase rotor windings, is that what you are refering to? Maybe that is what this motor is then.

So what is the difference between this and a Synchronous motor which uses it's amortisseur winding (induction machine) to get it up to pull-in speed? Semantics? Being that up until reading this thread I had never heard of a WRIM with single phase rotor windings, is that what you are refering to? Maybe that is what this motor is then.

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RE: wound rotors

edison123 (Electrical) 27 Sep 05 05:03

Two types of synchronous-induction motors. One is salient pole with amortisseur/damper winding start. This starts as sq cage motor using the damper winding and salient poles take over during synch run.

The other is wrim which starts with three phase rotor winding connected to rotor resistances and then near synch speed, with DC is applied to the rotor (with two of the shorted at line ends) to make it run as synch motor.

I have rewound both types of motors.

All these types of motors and electric braking are well described in 'Performance and design of alternating machines' by MG Say.

Regarding this thread, I also have not heard of in theory or in practice 'single phase rotor' in a 3 phase stator.

No jraef, it ain't semantics.Two types of synchronous-induction motors. One is salient pole with amortisseur/damper winding start. This starts as sq cage motor using the damper winding and salient poles take over during synch run.The other is wrim which starts with three phase rotor winding connected to rotor resistances and then near synch speed, with DC is applied to the rotor (with two of the shorted at line ends) to make it run as synch motor.I have rewound both types of motors.All these types of motors and electric braking are well described in 'Performance and design of alternating machines' by MG Say.Regarding this thread, I also have not heard of in theory or in practice 'single phase rotor' in a 3 phase stator.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

fsmyth (Electrical)

(OP)

27 Sep 05 08:47

Well, what do you think I have here? (Specs posted
previously).  The motor looks physically like any
other 286T frame, with the addition of the housing
containing the sliprings at one end.  I certainly
admit to not knowing enough about winding motors or
identifying rotor types, but I have read some of
what is available, and have found nothing that
resembles this motor.  Plenty of 3-phase rotor stuff,
but nothing on single-winding rotors except on
synchronous motors.  Would posting pitchurs help :)
<als>

(In case I have not posted it before, calls to
Baldor were not very informative, and the manufacturer
to which it was OEM'd has been absorbed by another, and
documentation apparently lost or non-existant).

RE: wound rotors

CJCPE (Electrical) 27 Sep 05 11:31

Pictures might help.

The nameplate data seems quite inconsistant with the idea that this is any kind of synchronous motor.

I think it would be worth the effort to ohmeter across the sliprings in both directions to see if there could be a rectifier in there.

RE: wound rotors

davidbeach (Electrical) 27 Sep 05 13:20

Dynamic braking is used by diesel-electric locomotives and they can be in dynamic braking for long periods of time bringing a train down a mountain grade.  DC injection wouldn't work well in DC traction motors, but even with AC induction traction motors, there is no way that the rotor could absorb all of that energy.

edison123, I've never seen dynamic braking defined the way you are defining it. Check Allen Bradley's description here: http://www.ab.com/drives/techpapers/RegenOverview01.pdf . They talk about pulling energy off the DC bus of a drive when the load is turning faster than the motor would would be. The energy is being absorbed from the load, converted to electrical energy by the motor acting as a generator, and being dumped as heat across a resistor. Dynamic braking does not heat the rotor any more than operating as a motor does and can be a long term operation. The DC injection braking you describe can only be used for very short periods as it dumps the energy into heating the rotor.Dynamic braking is used by diesel-electric locomotives and they can be in dynamic braking for long periods of time bringing a train down a mountain grade. DC injection wouldn't work well in DC traction motors, but even with AC induction traction motors, there is no way that the rotor could absorb all of that energy.

RE: wound rotors

CJCPE (Electrical) 27 Sep 05 15:56

I agree that "DC injection braking" or just "DC braking" are the more common and correct terms for applying DC to the stator. However I have ocassionally seen it called "DC dynamic braking."

RE: wound rotors

edison123 (Electrical) 27 Sep 05 16:57

when you say "I've never seen dynamic braking defined the way you are defining it", do you mean the definition or the process ? If it is former, may be it is then "semantics" (as jraef says). If you mean there is no such process (of applying DC to the stator winding to brake), then I disagree.

I have read the AB paper and it seems to be "regenerative braking" i.e. load driving the motor (supersynchronous speed). You may also see the book I mentioned.

I agree that not all motors can be braked electrically (dynamic braking, regenerative breaking & plugging) since electrical braking will overheat the rotor.

davidbeach,when you say "I've never seen dynamic braking defined the way you are defining it", do you mean the definition or the process ? If it is former, may be it is then "semantics" (as jraef says). If you mean there is no such process (of applying DC to the stator winding to brake), then I disagree.I have read the AB paper and it seems to be "regenerative braking" i.e. load driving the motor (supersynchronous speed). You may also see the book I mentioned.I agree that not all motors can be braked electrically (dynamic braking, regenerative breaking & plugging) since electrical braking will overheat the rotor.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

davidbeach (Electrical) 27 Sep 05 18:50

edison123,

Two basic types of electric braking:

Internal energy absorption and external energy absorption.

The DC injection method is an internal energy absorption method, the energy given up by the rotating load is dissipated in the rotor of the motor.  This method can only be used to bring a load to a stop, it can not be used as a means of speed control for overhauling loads.  This type of braking is principally applicable for induction motors.

Dynamic braking and regenerative braking are examples of external energy absorption methods, the main difference between the two is that in dynamic braking the energy is wasted as heat in resistor grids while in regenerative braking the released energy is returned to the supply system.  These methods can be used with DC, AC induction, and AC synchronous motors.  These methods can also be used for continuous braking - speed control - of overhauling loads.  Examples of overhauling loads can be elevators in one direction, mine hoist applications, locomotives, and undoubtedly many others.  With currents within normal operational ranges, there is no more motor heating, rotor or stator, than there would be operating as a motor.

Maybe some of it is semantics, but names for things work better if everybody uses them the same way.  DC injection is a means of braking an induction motor, but it isn't dynamic braking; to say dynamic braking while meaning DC injection doesn't convey to the listener/reader what you are talking about.

RE: wound rotors

edison123 (Electrical) 27 Sep 05 19:24

I agree that we disagree. Let's leave it at that.

davidbeach,I agree that we disagree. Let's leave it at that.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

Farkel (Electrical) 29 Sep 05 16:09

Maybe, just maybe the slip rings feed some other device as a secondary circuit like in a transformer.

RE: wound rotors

LionelHutz (Electrical) 30 Sep 05 09:15

I've never seen a 1-phase wound rotor in a motor before. I don't think this is what you have there.

Generally, for a wound rotor the rotor voltage is inversely proportional to the speed and the rotor current is proportional to the percent load. So if you've got a motor running at 80% speed and 70% load the voltage is 0.2 x rated and the current is 0.7 times rated. Use this voltage and current to calculate the resistance you need. It's not really this simple since you need to include the wiring and rotor resistance but it's a close approximation.

"The other is wrim which starts with three phase rotor winding connected to rotor resistances and then near synch speed, with DC is applied to the rotor (with two of the shorted at line ends) to make it run as synch motor."

I've never seen a synchronous motor with a 3-phase rotor. We've built field controls for 100's of synchronous motors and I've never run across that before.

The only brush type synchronous machines I've ever seen use a squirrel cage type of winding in the pole faces along with adding a resistor to the field winding when starting.

RE: wound rotors

edison123 (Electrical) 30 Sep 05 09:28

AEG (Germany) supplied such synch motors with wrim windings ( KW rating)and I have personally rewound six of them. The theory is in the book I've mentioned before.

lionelhertz,AEG (Germany) supplied such synch motors with wrim windings ( KW rating)and I have personally rewound six of them. The theory is in the book I've mentioned before.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

LionelHutz (Electrical) 30 Sep 05 10:00

I know it would work edison, I'm just saying a motor operating like that is not a normal synchronous motor. I suspect those motors were custom built for one specific application where they couldn't build a typical synchronous motor that could start the load.

RE: wound rotors

edison123 (Electrical) 30 Sep 05 10:08

I just posted to show that such motors do exist and do work.

Yep. They were for a specific application of a cement mill with a high starting torque requirement.I just posted to show that such motors do exist and do work.

* Anyone who goes to see a psychiatrist ought to have his head examined *

RE: wound rotors

shagooo (Electrical) 30 Sep 05 10:59

Electricpete - I think they had three, can't be 100%positive.  Typically these motors were used for the high torque applications (high duty cycle, short burst usage)and usually were screamin hot.  I would imagine the most durable motors made.  
I have also seen the eddy current brakes used with cranes and hoists.  These were powered seperately and the same resistor bank/contactor configuration was used but, inversely(and only on the lower command).  When the lower button was pushed, minimal braking was needed, as you increased the speed, the brake was working close to make so the load and motor would not "run away".
Interesting thread for an unuasual motor, working on those old cranes and hoist gave insight to speed control and braking amonst other system back in the day.

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