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
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
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
Sure hope management has some deep pockets. This course is not going to be
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.
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
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
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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