circulating current

Your AVR output voltages are not equal for load sharing therefore one is grabbing the load from the other and operating your reverse power trip on your supply breaker. Don't worry too much at this stage about you power factor, it's understandably very poor. Do what I've described below first and see how you get on.

Start by setting your NO-LOAD AVR voltage with the trimpot on the AVR to whatever you require (say 450V stator output), with the same instrument do the same to the other AVR's. Also check that the excitation equalising cables(s) between the AVR's is/are sound, it'll also go through connecting relays when you put both machines in parallel, it's not just the stators that are in parallel, the AVR's are in parallel too that's how you get load sharing - check that the relay contacts are good and not worn into a high resistance/bad connection.

I'm going to make the assumption that your prime mover's and engine governors are all working correctly, and that nobody has adjusted your compounding reactors, if that's the case you should be able to test run the alternators in parallel sucessfully..

Please correct me if im wrong, I think circulating current is not a problem...synchronizing of two generator has a settings. Must same frequency, voltage, phase. Most latest one has equipped with synchronizer to allow both generator all in right frequency, voltage and in phase before give a signal to share both. Reverse power happen when one of those stated are not the same. One will generate power and the other will load as motor. Here some point might help

1. Make sure the AVR of both Generator are working Properly

2. Check all the control wire of AVR might get loose, DC voltage supply, line to exciter

3. check all control wire from control panel to generator might loose or cut due to vibration

Hope this will help

Synchron...he hasn't a problem getting the alternators into parallel, his problem is keeping them there!

I agree with you, circulating current isn't a problem - until you have some. Frequency has to be slightly higher in the 'oncoming' machine to ensure that the alternator doesn't trip on reverse power as it goes into parallel and a load might be applied at the same time, and that all depends on your plant and control system setup. If the machines were out of phase when he paralleled I think he'd mention a different problem!!!

I'd like to think he knows how to parallel by hand, or at least has an auto synchro unit.

1) The reverse Power relay might trip due to motoring of one of the sets.It is not advisable.

2) The load sharing is not proportion to the rating of sets.

3) Droop setting is not correct.

4)Have you installed controller for proper load sharing ? If so what is the make ?

5) What is the rating of the set ?

6) What is make of Primemover ?

7) What is the governor ? Is it Electronics /Hydraulic ?

8) What is the make of alternator?

9) Does the alternator fitted with AVR?

10) Does the alternator fitted with quadrature current compensation CTs,are these connected ?

11) Dose the set trip immediatelly after synchronizing or after loading

12) Were the sets already commissioned and running or just commissioning ?

13) What is make of reverse power relay ? Is it reverse power relay or reverse kVAr relay

we can give proper solution/suggestion provided you give relavent inputs.

hi,ramivod

please contact me at the following address

issatalamas@hotmail.com

its 245kw marine generator,prime mover make-cateerpiller c9 series engine coupled with leroy somer alternator.

yes there is quadrature ct is fitted and connected.governor type - electronic.

the set is not tripping once itwas paralled after few seconds one generator losses its speed and goes to reverse power.

the set was commisioned earlier. dief controller controls the machine for all the protection system.

As I mentioned earlier, the 'oncoming' machine to the bus-bars has to be slightly faster - the synchroscope will indicate a clockwise rotation SLOWLY. You now have on the other hand, if I understand you correctly, that as soon as the machines are in parallel one machine slows down and sheds it's load operating the reverse power trip. That is correct and what I would expect to happen.

So do you have a mechanical problem with the governor? Is the fuel rack free to move? Are your fuel booster pumps working? Have you got fuel pressure up to the rail? Is the engine stopping or just slowing down? Does the engine recover it's running speed after the reverse power has operated? Have you done the AVR voltage checks that were mentioned earlier?

One liners ain't very helpful to anybody, expand your problem when you've sorted out the correct symptoms and tell us what checks you've done so far.

It Looks to me one of the controllers is not sending signal to the machine.Check connections between the controller and the machine.

The synchronizing, is it done manually or automatically through controller.Before synchronizing does the controller send signal for speed increase and decrease ?Your answers should be elaborate and you must give as much information as possible.One word quiz answers will not do for us to visualize the problem

Have you got control of your engine on the switchboard? If you run at 60Hz take the speed up to 63Hz then down to 57Hz (ON NO LOAD of course!) or keep the speed variation between the high/low frequency trips if you have them. Do this a couple of times to establish you have control - This is a fundamental check prior to paralleling and should be carried out every time.

If that doesn't work go back to the previous answer and work out why you have no electrical speed control.

To analyse the problem first we should know the following points.

1) What is the capacity of both the generators

2) Is the phenomenon is happening with only one generator or both.

3) What is the prime mover and its type of Governor(Electronic or hydraulic)

4) Are both the machines new.

5) Whether Low Forward power Relay is there in the system or not

6) If the Primover is equipped with Electronic Governer then please let us know the droop setting of both.

If above clarification is given then we can put our mind in to it.

Rangacharya

1) Check your voltage droop setting ( Should be equal)

2) Check your Droop CT Polarity

3)Are you using single neutral earthing system

4) Do you have automatic kW/ kVAr sharing. If not manually you have to adjust the voltage to equalise the reactive power after sync.

5) If you sync. two different make of alternators check the specs for parallel operation suitability

The problem seems to be as under please go through my comment and correct me if i am wrong.

As per the proceedings of this posting i under stand that when second generator is being synchronised it is tripping on reverse power.

The above phenomenon can happen if the minimum power set in the electronic governor with time should reach before reverse power relay operates. That is why in my earlier posting i had asked whether alternator is equipped with low forward power relay ( We may call it as I stage of reverse power). Always in an electronic governor there is a option to set for reaching minimum load without human intervention, other wise the operator has to be quick enough to take the load before it trips.

Please check your electronic governor (If it is installed) for this setting.

We faced similar problem of STG tripping on Low Forward Power relay instead of Reverse Power.

The minimum load setting will be 10% of Rated Capacity that means it will be 1.5 MW for 15 MW machine. When the machine is synchronised then load goes automatically to 1.5 MW without human intervention.

rangacharya

Forgetting the checks on rating/setting etc of equipment, I will suggest to check if your incoming generator RPM is bit higher but within synchronising limit, to pickup some load at the moment of synchronising.Let me know the result.