On Sun, 6 Mar 2005 15:30:50 -0500, "ATP*" wrote:


"Don Foreman" wrote in message
.. .
On Sun, 06 Mar 2005 16:52:53 GMT, "Karl Townsend"
remove .NOT to reply wrote:

If there's anyone out there with Total Recall, you might remember I've had
a
lot of trouble with my irrigation well. Its a 20 hp single phase and they
aren't made or serviced anymore. I have to move up to three phase.

I've bought a 50 hp VFD drive and a 75KVA transformer to produce 440 three
phase. Before I buy and install a new 30 hp. pump, I want to test this
under
load. I have a 30 hp motor, I'm looking for ideas on how to create 30 hp
of
mechanical resistance and know I have that much load.

For how long? 30 HP is over 22 KW, a fair amount of heat.

For short-duration tests, you might use an automotive drum or disc
brake. You can measure torque with a spring scale. At 1750 RPM,
torque would be about 90 lbf-ft so a 1-foot arm and a 100 lb spring
scale would be about right.

Most VFD's will read out torque, current draw, etc.. I suppose it's all
derived from the speed and current draw, in any case there should be enough
information to determine whether the VFD/Transformer combo can handle the
load. I would monitor the voltage output of the transformer during the test.
You can reduce the voltage output from the VFD, within its range. I don't
know if it would react quickly enough to stabilize dips in the transformer
output.

I forgot about the VFD. I don't think you'll get anywhere near 30 HP
out of a nominally 30HP motor slowed that much with a VFD. It's
current (and current-produced heat) that determines the power rating
of an induction motor. You can run it slower by dropping the
frequency, but since torque is proportional to current the torque
can't rise much -- so you have less power because power = torque *
speed.