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Dc motor series field with a regenerative dc drive
- Thread starter cccelcj
- Start date
Skogsgurra
Electrical
If you by series field mean a motor with just one field - and a series one. Like a traction motor, you cannot use it with a standard four quadrant thyristor rectifier. But you surely can use it with a specially designed thyristor rectifer. It is being done all the time in traction applications like trains and the like.
If, on the other hand, you mean a standard DC motor with a series field, then you have to tell if the series field is there to stabilize speed aka negative compounding or if it is there to improve load sharing, positive compounding, when several motors run off a common DC source.
In the former case (stabilizing), the series field weakens the main field when motoring and strengthens the main field when braking.
Strengthening the field when braking means increasing the EMF and that can make the thyristor rectifier trip on commutation error (meaning fuse and collector break down) if you are close to top speed.
If the series field is there to improve load sharing, increased load means increased field strength when motoring and reduced field when regenerating. That would be non-critical.
Answer: It depends. As usual.
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
If, on the other hand, you mean a standard DC motor with a series field, then you have to tell if the series field is there to stabilize speed aka negative compounding or if it is there to improve load sharing, positive compounding, when several motors run off a common DC source.
In the former case (stabilizing), the series field weakens the main field when motoring and strengthens the main field when braking.
Strengthening the field when braking means increasing the EMF and that can make the thyristor rectifier trip on commutation error (meaning fuse and collector break down) if you are close to top speed.
If the series field is there to improve load sharing, increased load means increased field strength when motoring and reduced field when regenerating. That would be non-critical.
Answer: It depends. As usual.
Gunnar Englund
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
- Moderator
- #3
Skogsgurra
Electrical
Not at all. They just weaken the field under the brushes. Not aware of them being a problem.
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
Gunnar Englund
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
- Thread starter
- #5
Yes, this is actually a shunt motor with a series field. I figured it to be a compund motor. However I have heard this motor being referred to as "stabilizing shunt". I do not know the difference. The drive could not be tuned because it was overrated for the motor which is very old. We ended up removing the regen drive and installing a drive with dynamic braking. The new drive is also now more closely matched to the motor.
- Moderator
- #7
Is that negative or differential compound for improved speed regulation and cumulative compound for better starting torque and better start current curve. It's been awhile since I worked with DC motors every day.
Bill
--------------------
"Why not the best?"
Jimmy Carter
Bill
--------------------
"Why not the best?"
Jimmy Carter
waross
Cumulative compounding is for better starting torque and maintaining a steady speed.
Differential compounding is rarely used since under overloads, the working flux will be reduced, the motor will tend to race taking in a still larger current. The point may be reached where the series field will overpower the shunt and the motor will reverse.
Cumulative compounding is for better starting torque and maintaining a steady speed.
Differential compounding is rarely used since under overloads, the working flux will be reduced, the motor will tend to race taking in a still larger current. The point may be reached where the series field will overpower the shunt and the motor will reverse.
- Thread starter
- #9
- Thread starter
- #10
The reason I asked was because on more than one drive (this one included), when the motor was stopped, it the went in reverse for maybe more than a complete revolution. could this have due to regenerative effect, or the series field overpowering the shunt field?
cccelcj
The motor reversal would depend on how powerful the differential series field is as compared to the shunt field and how much was the load current.
Is the shunt field supply switched off during regenerative braking ? That could explain the motor reversal.
The motor reversal would depend on how powerful the differential series field is as compared to the shunt field and how much was the load current.
Is the shunt field supply switched off during regenerative braking ? That could explain the motor reversal.
- Thread starter
- #12
Don't quite know what the drive is doing at the time. However, the drive that I just recently worked on was in field weakening at the time. Motor speed range is 400 - 1600. The drive top speed is set at 1200. Part of the problem I encountered while tuning is that there is no field data. The motor was tested in a motor shop with 240vdc on the field. The Reliance drive can only put out 150vdc. At 1200 rpm, I measured the field current to be .1 amp.
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