Locked rotor test for a 1000 HP DC motor
Locked rotor test for a 1000 HP DC motor
(OP)
The customer who is visiting my facility in a couple of days wants to test his new drive and he s bringing in his 4160 volt drive. We have a GDY-37 generator set coupled to a 1000 HP motor which is capable of running in 4160 volts with an FLA of 124 amps. Now the problem is that, the customer wants to see how a locked rotor condition would affect his drive. We haven't done locked rotor tests in our workshop and since am a new hire, i dont know how to manufacture a brake assembly for such a large motor. Can some1 please guide me on how to lock the rotor (possibly for a time of 15-25 seconds) for a 1000 hp machine?





RE: Locked rotor test for a 1000 HP DC motor
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
RE: Locked rotor test for a 1000 HP DC motor
I think for large motors, the locked rotor testing is typically done at reduced voltage and results are scaled up.
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
To make it more interesting, the motors had to be tested in groups. The largest group was 8 x 1300 HP motors on a common drive that had to be tested simultaneously. We didn't have a large enough set of vice grips although I have seen the shafts of large DC motors clamped for locked rotor tests.
We used jumpers across the brush holders to simulate locked rotor conditions. The drive really can't tell the difference between a jumper and a locked rotor. Yes there may be a slight error but it is conservative. The error may be reduced by selecting jumpers of a smaller gauge the the feed conductors. I would use jumpers sized at about 2/3 of the ampacity of the feeder conductors. This is the equivalent of sizing the feeders for conductors in a conduit, and sizing the jumpers for conductors in free air. The jumpers will be in free air so this will be safe and will reduce the already slight error.
PS, Lift the brushes!
Bill
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"Why not the best?"
Jimmy Carter
RE: Locked rotor test for a 1000 HP DC motor
Thyristor drives need the inductivity in the armature winding to perform properly. If you short-circuit the armature (jumpers), the current controller will not work as intended and your test will not say much about what really happens when rotor is locked.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Locked rotor test for a 1000 HP DC motor
Bill
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"Why not the best?"
Jimmy Carter
RE: Locked rotor test for a 1000 HP DC motor
You mention a 1000HP DC motor and then a 4160V drive...Sorry, there is no such thing as a 4160V DC motor, you must mean something else.
Why not send a sketch or dwg of the setup.
In any case as suggested by others, jumpering out the armature (rotor) and lifting the brushes of this (unfortunate) DC machine will result in zero torque, as there is then no current at all through the armature (rotor)...no need to lock the rotor, then.
It all sounds a bit flaky, why not explain more to us..before you melt down anything or hurt someone...
rasevskii
RE: Locked rotor test for a 1000 HP DC motor
Bill
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"Why not the best?"
Jimmy Carter
RE: Locked rotor test for a 1000 HP DC motor
Scott
I really am a good egg, I'm just a little scrambled!
RE: Locked rotor test for a 1000 HP DC motor
But the suggestion was made to disconnect the shunt field to do locked rotor testing. Even if you disconnect the shunt and series field on a shunt or compound motor there are still the small commutating poles in the armature circuit. I wouldn't want to take a chance without the shaft being mechanically locked.
Bill
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"Why not the best?"
Jimmy Carter
RE: Locked rotor test for a 1000 HP DC motor
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
RE: Locked rotor test for a 1000 HP DC motor
We all take safety seriously (although not every post needs to dwell on it).
I would be mad at myself if I had suggested something blatantly unsafe, and I think we all would rightly judge anyone who did so.
When Bill's recap indicated (with no bad intentions) that someone else (turns out to be me) had suggested to run the motor without field, I wanted to clarify the original context, which included plenty of cautions on my part.
It is time to move on to more productive things for both of us, I hope.
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
Sorry if i offended.
RE: Locked rotor test for a 1000 HP DC motor
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(2B)+(2B)' ?
RE: Locked rotor test for a 1000 HP DC motor
Before testing, you need to answer a few questions:
What is being tested? Is it the control's short-term capability to deliver locked rotor current? Does the control have a bypass contactor for 100% on-time, or is current electronically limited by current sensing and reducing on-time? If the control switches from 0% to 100%, does it need motor and distributed circuit inductance to achieve its switching ability?
Where I'm going with all of this is that if you're testing the control's current capability, and inductance isn't required, why don't you measure the cold DC resistance of the motor, make up a dummy resistive load and test the control without a motor, etc.?
NIKT1
PS: If you must test with a motor at full voltage, you will need a beefy means to lock the rotor. You will need some idea of the anticipated torque and design a means to lock the rotor more securely than a V-belt and pulley system. I have performed many DC motor tests(albeit at <=120 Volts) and we usually test at reduced voltage and with a substantial locking bar.