Generator Amps Needed: Siemens Soft Starter Sirius 3RW44 to Start 230 kw Motor?

I have some doubts about the entire rationale here, but I don't yet see the total picture. The pump motor is about 38% of the genset kw capacity, so I am surprised that it won't start, especially with a soft starter. Does this genset have other loads on it? If so, maybe they could be disabled momentarily while starting the big motor, and then brought back on line.

You don't mention the FLA of the motor, which should be about 450A; rough guess. Once again, it seems that the genset's rated 1140A should be able to handle this on a soft start.

If the pump is the only load on the engine, why not skip all the electrical confetti and just drive the pump directly? No motor, no starter, substantial money savings.

This is the only load on the generator. The startup amps on a direct drive is definitely too high for the generator (apparently "typically five to six times the full load amps (FLA) of the motor"), so we need a "soft start". I am not sure what the FLA would be on this motor. The plate on the motor has 415A. I assume this is the amps required to run the electric motor.

well you can test your gensets load carrying capacity on saorate load bank, may be your genset is not able to take load its rated for?

may have some problem in alternator chek its no load full load voltages and currents, if all is well than its not genset problem

I don know much abt siemens soft starter , but i know abt ABB or schneider soft starters....i believe they r very much similar............check this link on soft starter common settings.....u may get some hint....

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/2985284834bcff7fc1256f3a00274038/$File/1SFC132002M0201.pdf

I am surprised that Siemens engineers failed to setup a softstarter.

750KW genset is more than enough to start a 230KW motor with a softstart .....You or the comission engineer should check carrefully the parameters of the softstart, you may set a longer start time with a current limit within the safe limit of the generator, when driving a pump, special setting of the sofstart should be performed, enabling a high torque at startup.

if still failed, you should consider using a VVF in lieu of softstart, starting current will be as low as the nominal current of the motor...

I am very familiar with the Siemens 3RW44 soft starter and I can tell you from here what the likely problem is.

If it is tripping at 110% current, that says to me that someone selected your soft starter as a "light duty" application, even though the Siemens literature doesn't specifically state that; and therein lies the flaw. The 3RW44 can be purchased based upon the expected starting duty of the load application. You have to pay careful attention to the specifications pages of their catalog, not just the selection guide, which is optimized to offer the least expensive option.

So the problem has nothing to do with the generator size, that should be plenty of capacity to do the job. The problem is, someone probably selected the cheapest sizing selection for the stated motor power and the soft starter itself is incapable of delivering enough power for a long enough time to suit your needs and is shutting down to protect itself.

You didn't state the size (part number) of the 3RW44 nor the type of "pump" you are trying to start; not all pumps have the same requirements. If you let me know all of the information you have I can tell you which starter you should have used.

If it turns out you have the right version after all, then the other less likely situation is that you have an older (or cheap) generator with an AVR (Automatic Voltage regulator) that is being affected by the harmonics created by the soft starter when ramping the motor. This used to be a very common problem, but years ago the generator mfrs figured out that they had to add filtering to the AVR circuit. Old units may not have that filtering, cheap ones sometimes don't bother as well.

Hi JRaef:

Siemens technician has the soft as 3RW4447-6BC34.

The pump is a floating pump connected to the motor by a chain. Pump is the axial flow type, so drives water and has no suction head. 2.7 m3/sec delivery, 5 m total dynamic head, 480 rpm.

OK, so that unit is rated for, at best, 432A but that's at 40C, 10 second maximum ramp at 300% current limit. If the ambient is 50C, it's only rated for 385A under the same starting conditions. If the ramp time goes out to 15 seconds, it's rating drops to 402A @ 40C / 385@50C and at 30 seconds ramp time it can only take 285A@40C / 260A@50C.

But from your post in another forum it is tripping on Over Voltage, so more likely it's a problem with the AVR filtering in my opinion.

Thanks so for for this help. I have made more ground here in 2 days than in the last 4 months!

I am waiting for the AVR specification from the generator supplier.