motor starting problem with generator 1

[bedane]

hi all
we have installed 130 kw motor with a star -delta starting system to be driven by 280 kva new generator.but when we test the motor with the gen-set . the motor starts to run but the engine will stop running when the delta contactor closes.( with out the generator breaker tripping ),
the geset supplies only the motor no other load
the altitude here is around 2400 above see level.but i have seen on the generator manufacturer catalog it says it can work with the above stated rating without any deration for up to 3000m above see level.

is this the rating compatibility problem b/n the generator and the motor.
can it be adjusted without changing both machines.
best regards

 

[davidbeach]

You'll never have good luck with an open transition wye-delta starter, don't bother trying to adjust it. If you can convert it to closed transition, you'll do better. You may well find your best results with across the line start. If you can unload the motor for starting, you could direct connect it to the generator and start the motor by ramping up the generator. No inrush at all.

 

[Steven1984]

You could try using a soft starter, this will limit the voltage drop seen by the generator and will also reduce the stresses on the motor and load.

 

[iop95]

May be 2 problems; one is control unit of diesel engine, it's not fast enough to allow such step load increasing. Check if you can adjust parameters of control unit (99% a PID regulator); second (or cumulative to first) is air density at 2400 altitude which is about 26% smaller than at sea level and may be a problem to assure enough compression for a cold diesel engine with high step load. Regarding manufacturer catalog derating, this may be true for nominal regime and with respect to maxim allowed engine temperature and not with respect to transient loads stability speed.

 

[burnt2x]

What David said. A one-on-one direct connection: motor connected to generator right at the very start; the moment the generator builds up voltage the voltage goes straight to the motor. Motor spins as the generator speeds up. The same effect as a soft starter,IMO.

 

[waross]

Just going DOL may do the trick. If the motor slows down the generator, the UFRO function will reduce the voltage and ramp the voltage back up as the speed recovers.
Step #2 Direct connected DOL before starting the generator. This will probably work with a PMG generator. It may work with an output powered AVR.
Step #3 You may have to use a UPS to supply power to the AVR. Then the UFRO function may emulate the action of a VFD.
Note: If you have an AVR with common power and sense terminals you will have to change it out for an AVR with separate sense and power terminals.
TLA's:
AVR Automatic Voltage regulator.
DOL Direct On-Line.
PMG Permanent Magnet Generator (A small alternator which supplies power to the AVR.)
TLA Three Letter Acronym.
UFRO Under Frequency Roll Off.
UPS Un-interrupt-able Power Supply.
VFD Variable Frequency Drive.

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

 

[bedane]

Dear all
thankyou so much for your fast and good answers.
based on your suggestions i have told the technicians there at the site to do some of the suggestion you gave me and
when we tried to increase the time on the timer we have found out the engine stops after the voltage and frequency drops before changing to delta ( within two or three seconds before the motor reaches its full speed while it is on the star connection) i.e we were mistaken earlier to say the engine stops when the starter changes to delta.
I am going to the site in the remote area 500 km from where i am now,the day after tomorrow to check the last possible options and make the last decision
do you still think it is possible to adjust the generator or the motor starter so that we can use the existing system?
or do we have to change the star delta starter with the solid state starter or vfd starter?can this starter work ?which one is better for this problem?
If this is not possible we are planning to change the generator which will be very expensive.
Based on you suggestion I will start the generator and the motor all together .with the star delta starter connected but with the generator starter key as a starter first if it doesnt work. I will try it as DOL.
i will also try to adjust the AVR based on your suggestion

I would be glad to receive all the possible option which i can try at the site .
best regards

 

[rasevskii]

As waross has said, it depends on what type of excitation system the genset has. If it has a PMG supplied AVR system you are in better luck than if the AVR and excitation system is supplied from the stator voltage which will be very low on start-up as the DOL connected motor looks like a short circuit as seen by the generator.

From the spec of the genset you should be able to go to the genset OEM to get info on how the excitation system works. This should be done before going to the remote site.

Also what type of control system the genset has. "Catserveng" our resident genset expert may be able to give some expert advice if you know he OEM and model.

BTW what is the motor driving? Is this an unloaded start?

rasevskii

 

[waross]

Check the engine controls of the generator. From your description it sounds as if the generator engine is stopping. If the engine controls have a low speed shutdown you may have to disable it.

Based on you suggestion I will start the generator and the motor all together .with the star delta starter connected but with the generator starter key as a starter first if it doesnt work. I will try it as DOL.

I didn't see that suggestion anywhere. Oh well.
You will have to have the star delta starter pulled in or blocked in mechanically. The controls may not work to pull it in electrically when the frequency and voltage are low as the generator ramps up.
I doubt that a soft start or a VFD will be suitable. The harmonics that they create often interact badly with the AVR.
Take a UPS, about 500 or 750 VA.
Arrange the star delta switch for DOL starting.
Supply the starter with the UPS.
Supply the AVR with the UPS.
Check that the genset does not have any low frequency shutdowns. Disable them for starting.
Check that the gen set does not have any circuits that disable the generator output until the generator comes up to speed. Disable them if need by.
With the motor direct connected to the gen set and the AVR powered by the UPS. Start the genset and the motor should start with it.
Is this a newer gen set? If the gen-set is more than 20 years old, the AVR may not have UFRO and you may have to fit a new AVR.
If the gen-set has a PMG, it may work but you may have to change to an output powered AVR.

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