convert a slip ring motor into a variable voltage transformer?
convert a slip ring motor into a variable voltage transformer?
(OP)
Someone told me it is possible to convert a slip ring motor into a variable voltage transformer? If so what would be the set-up? We often have problems running up larger AC induction motors unloaded (380v/50Hz). Our present test bench doesn't cope too well when running motors over 250kw





RE: convert a slip ring motor into a variable voltage transformer?
Google "induction regulator" to see examples.
The first one that turns up is quite good: http://www.geocities.com/cindulkar/lab17.pdf
You need an electrician with good knowledge to do this.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: convert a slip ring motor into a variable voltage transformer?
Pardon my somewhat limited (and rusty) electrical knowledge. I checked out the diagram you kindly linked. To me it didn't seem far away from an auto transformer of sorts. I am assuming (depending on the voltage ratios) that either the rotor or stator could be used as a primary, would that be correct? Could a similar setup be used as a variable voltage test output for motors up to say 400kW? (providing we can find a suitable slip ring motor).
RE: convert a slip ring motor into a variable voltage transformer?
It does not work like an autotransformer. The action depends on the rotor voltage being phase rotated to buck or boost the line voltage. You can have any voltage in-between, depending how you rotate the rotor. For 0 - 200 % of line voltage, you need rotor voltage = line voltage.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: convert a slip ring motor into a variable voltage transformer?
I think I'm with you so far (or at least I hope I am). Imagine a S/R motor having a 400v stator & 230v rotor. We could in theory hook-up the rotor as primary 230v & get a stator output 0-460v variable at the same frequency? What then happens to the stator/rotor nameplate currents? are these to be regarded as maximum input/output values or is that too much to hope for.
RE: convert a slip ring motor into a variable voltage transformer?
1- Torque developed by the rotor when the load and rotor current increase. How will you keep the rotor locked and how it will be moved to adjust the desired voltage?
2- If the stator voltage is fed into the rotor winding neutral. Do the rotor winding and brush/slip rings have enough insulation to handle the increased voltage. Normally the rotor voltage is designed, constructed and insulated for a fraction of the stator voltage.
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
For 2 poles the geometric degrees (G°) are the same as the electrical degrees (E°). For 8 poles to displace 90°E you move 90/8/2 = 22.5 ° geometric.
WRIM = Wound Rotor Induction Motor.
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
Wound rotor induction motor
"is it feasible?"
I have seen a motor repair shop that had a WRIM permanently set up to provide a variable voltage source for testing a variety of motors.
"My intuition tells me that the rotor would have to be securely locked with a hefty gear reducer, motor drive, limit switches, etc"
That sounds similar to the setup I saw. They had a gearbox connected to control rotor position.... low speed high torque side was connected to the WRIM, the other side was connected to a small high speed low torque reversible motor used for control. Don't remember about braking.
"What I am not sure of is the actual polar movement required to vary from min to max secondary output. If this movement is small then why not just dispense with the rings/current collectors & mount appropriate cable connections instead?"
The angle of movement for full change of voltage is small... I think it is the span of one pole or less. The setup I saw had hardwired lugged connections between rotor and stationary power supply as you said.
The EASA Technical Manual has a detailed writeup on converting a slip ring motor for use as a variable voltage source. A great reference if you can get your hands on it, but pretty expensive. Most motor repair shops in the US have a copy.
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RE: convert a slip ring motor into a variable voltage transformer?
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Eng-tips forums: The best place on the web for engineering discussions.
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: convert a slip ring motor into a variable voltage transformer?
the other thing to be aware of is overheating. The motor will be designed to cope with the full current at rated speed - at zero speed there is no cooling. You could add some blowers or fit some thermpcouples to the rotor. It depends on how long you want to test for.
These method is alos used for exciters on variable speed synchronous motors where excitation isrequroed at zero speed.
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
RE: convert a slip ring motor into a variable voltage transformer?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: convert a slip ring motor into a variable voltage transformer?
Small world huh!