Motor Starting Problem with Generator

sorry the motor is induction motor

Load on motor at start up? Time adjustment for delay of delta switch over?

Not a big problem, just increase more 2 seconds time at star condition.I believe it will help you out. And monitor the ammeter,voltmeter readings while the starter is shifting from Star to Delta.Another possibility can be if the readings are abnormal when changes to delta then must do check your delta contactor's contacts either latching properly or any demages are there, check it Last option is that go for softstarter or VFD.

1) While change over between star to delta, the current change to be smooth, this depends on setting of star delta timer, then there will not be any jerk and transition current will not affect the engine.

2) For any electrical transition current problem or voltage dip problem only the DG breaker should have tripped-Please examine

3) If the engine trips please findout the reason,the engine should not trip,

Normally the engine trips for the following abnormal conditions:

a) Low Lub oil pressure

b) High engine water temperature

c) Over speed

d) Low engine fuel Pressure

What type of motor is it(design A,B,C,D etc), determine starting kVA/hp?. If within limits check the engine,check cable size from gen to motor and other electrical parameters too.

What is the driven equipment and how it is connected to the motor?Star delta or any starter does not reduse starting current as is commonly mis understood even by engineers some times.It only reduses the time for which Starting current persists.Pl let us have load details .Only then a proper analysis can be carried out.

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.

Some one have suggested me to start the generator and the motor all together .that means i will change the starting system so that when the generator starts will automatically stars together.so that this will have the same effect as the soft starter with reduced voltage staring system .do you think it will work?

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

best regards

Try by reducing the timing between star and delta.

Please connect the motor to the mains and adjust the timer for smooth transition.

then connect the motor to the generator source and try.

The starting current of the motor should not be greater than 200 % of the Generator full load current, as a general rule.then this problem may crop up.

Further in your case there will be deration due to altitiude.

If the problem persists then you may have to change the starting method of the motor to soft starter.

Also let us know the cable size between the generator and the motor.

Why don't you try a closed transition star-delta starter?. Still you didn't tell us what is the load connected to the motor.

OP, the problem may require no more than some governor tuning. You have not described the nature of the load on the induction motor but I suspect it is rotary with a high moment of inertia and/or starting torque. A clue as to what is happening is your statement about the gen-set tripping a few seconds after the motor has accelerated but just before the transition.

Here's what may be happening, by increasing the start time you have accelerated the load beyond the point where its speed-torque curve crosses above that of the generator, thereby quickly unloading it. This transition can take place very rapidly and has the effect of rapidly unloading the prime mover which will then throttle back to prevent overspeeding.

Think of it terms of driving a car up a very steep hill, you floor the throttle to maintain speed and climb the hill, but when you reach the top and see that it's almost straight down on the other side you immediately pull your foot off and hope that the engine goes from wide open throttle to idle without redlining or stalling. There's probably a governor setting for minimum idle speed, try boosting it and see if that cures your problem. Think about it when you're on your drive there.

oh sorry for not telling u the load type

the motor is used as a surface pump for water

best regards

Pl furnish details .Is it a centrifugal or reciprocating pump.In any case a simple solution will be intoduce a fluid coupling between the motor and generator which will allow the motor to start practically unloaded.A scupe type will be better.Secondly are u starting the pump with discharge valve closed or openIf close the discharge valve and slowly open as the motor shifts to delta you may not have the problem.In that case u can avoid fluid coupling too.

Dear all

here are the result

first i have adjusted the potentiometer on the AVR (UFRO) .then the generator starts and run the motor properly .it changes to delta without any problem then after it works for one hour pumping water we stopped the generator and restart it .but at this time the generator takes the load but after 4 to 5 seconds the current starts to raise and the overload relay starts tripping before the connection is changed to delta .after observing this problem i reduced the time on the timer after that it starts working properly.I think the last problem is due to the back pressure from the water in the pipe.

thank you all again

best regards

If none of the above solves the problem, then call the <...gen-set...> manufacturer and arrange a site visit.