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motor with softstart
2

motor with softstart

motor with softstart

(OP)
I got a motor 690 V 15 kw 50 hz, for moving a compressor with a load demand on 12,6 kw and 73 Nm, and speed 1750rpm and 60 hz, and my question is this motor suitable for this application, the idea is to start up with a soft start, and the load on compressor increase with speed... in 750 rpm it´´s about a 50 % of nominal load....my calculations says that with the new speed i got a torque on 85,6 Nm...and i think it´´ll be enough...how do you see? remember that after reaching nominal speed the soft start will be by passed....
thanks  

RE: motor with softstart

Quote:

load on compressor increase with speed.
Is the unloader broken? At this size compressor the unloader may be an automatic mechanical device. If an automatic unloader loads the compressor at too low a speed it may stall. If that may be the case set the soft start to accelerate as fast as possible. The compressor may need to be turning fast enough to have some flywheel effect before the unloader loads the compressor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: motor with softstart

(OP)
thaks... "i said that load on compressor increase with speed", this is what i saw in the manual given by Bitzer.... but i didn´´t test it...still on study phase...just i want to know if it´´ll be enough... or if i forget something on my calculations
 

RE: motor with softstart

Let me see:
Your motor's full-load torque = 15kW X 9550/1750rpm = 81.85 Nm.
Your load torque requirement is 73 Nm @ 1750rpm (13.37kW at shaft, not 12.6 kW as you posted).
You have just enough motor power if your motor is 89% efficient. Most compressors do not load up immediately but follow what Bill said, you need to bring the motor up to speed before the loader valve kicks in.

RE: motor with softstart

Hi burnt. At 15 kW, many of the unloaders blow off the trapped gas on shutdown, but allow the compressor to begin pumping almost immediately. You may have only two or three revolutions before the compressor is trying to pump full out.
We have both said it but one more time, get up to speed fast if you have an automatic unloader.
Bigger compressors are more forgiving.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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