DC motors

Hi Guys
Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor.
Thank you Regards smitha
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What are you trying to do?
I have found that testing can be done with out removing the motor if you have the right equipment. Having the spare 20 kw drive around is just not an opinoin where I work.
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I need to write a test plan/ procedure how in vaious methods we can bench test a 20Kw motor rated with 260-350 volts. we have motor in our lab so we need to test the performance of that. do you have any suggesstions for that thanks regards
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not an

Your going to need something substantial to bolt it down. Torque on a 25 hp motor can surprise ya. Next your going to need a load. I suggest a generator and resistive heaters in stages that can be switched on and off at will. This load should be go beyond the service factor of the motor. The lab should be able to be cooled and heated along with the humidity levels so that you can actually see real life applications. Motors are installed in some pretty dirty, ugly hot and humid places. All that has to be taken into consideration. Your going to need some calibrated test equipment. Volts, amps, rpm, megger, possibly a hi pot. I have used a hi pot on low voltage motors because that is the method that the engineer asked for, usually you do not.
Your going to need a calibrated power supply so you can do high and low voltage.
Sure hope management has some deep pockets. This course is not going to be cheap. http://www.avotraining.com/training/index.asp
http://www.reliabilityweb.com/fa/motor_testing.htm
http://www.magtrol.com/motortesting /
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The first thing to do is check whether the motor is a self excited one either a externally excited one. Once you have the information you might write down the equations which define the motor. On a second step you might measure the resistance value between the wirings available to control it. You might work out the speed and torque constants. Speed and torque can be indepently controlled in case you got a externally excited motor.Otherwise you just can control one of them.

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Guess it depends what you mean by 'bench test'. Certainly insulation resistance checks and correct wiring checks are easy enough.
A good 'bench inspection' would include the brushes for signs of chatter, arcing, proper seating, etc. The bars and mica would be inspected for 'fins', dragging, excess wear and other problems.
Bearings and such for excessive 'play' either axially, or radially.
If the rotor is pulled, a simple compass along with a small current source can be used on the field windings to verify correct polarity (more than once I've found two adjacent shunt coils with the same magnetic polarity after being rewound by others ;-). Also the correct relationship/markings for any series winding and interpoles (if any).
Finally, after satisfying myself that these things are correct, I'd start *considering* powering up the unit. But DC motors like the size you're talking about require specific starter/controllers. Connect the thing directly across the line and you'll ruin it. The starter must be sure to apply full field current and series starting resistance that gets shorted out as the motor accelerates (either simple time-delay, or armature-current-sensing are common). Once fully started, then and only then allow field reduction.
Or... If the unit uses a modern solid-state control, then it would need to be available 'at the bench' to start the motor.
As others have said, be sure to provide adequate mounting. A 150 lbm motor left loose will jerk itself across the shop and break somebodies leg in just a second.
Now, if you still want to start it up 'on the bench', you might consider a dyno to load it. Obviously, the more load on the motor, the more torque is exerted on the mounting. So bolt the thing down using *all* the mounting bolts.
daestrom P.S. NEVER try to start a shunt or compound motor without field current. And NEVER start a strictly series motor with no load attached.
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