Generator Speed Shift 3

[gokmen]

Hello Friends, I have just joined this helpful site. I am an electronic engineer who is working as Operation and Maintenance Chief at a hospital. There are 2ea Alternators (SDMO-400V/50Hz/1000kVA) that are each driven by Diesel Engines (Cummins KTA50G1, 1500rpm/50Hz) as Emergency Power source for the building. The building's power demand is about 700kW. If any commercial power outage is detected both of the generators comes up and the generator-G1 connects to emergency busbar and first load group swithing to emergency side in 3 seconds. During this time generator-G2 decreases its speed and tries to synchronize to the emergency busbar. After the synchronization (about 30 seconds) period G2's C/B closes and coupling to emergency busbar is achieving. After this point G2 takes about 50% of the load on the busbar and other load groups connecting to emergency busbar sequentially. This is the scenario. Governor Setting is 1500 rpm with 1% droop for G1 and 1540 rpm with %3 droop. There are RG491 modules in each generator's control panels.
And the trouble I have on the Generator Sets is:
While G2 decreasing speed and trying to synchronize to G1, G1's speed begins to increase and after that G2 tries to increase the speed and catch the G1. Is that normal? What I think is G1 should remain at the adjusted speed at least untill G2 connects parallel and load sharing takes place.
Thank you very much for any help.

 

[nawao]

I suggest to set droop at same 3% in both gens. Adjust the speed of G2 in order to shorten synchro time "(about 30 seconds)" as short as possible.

 

[waross]

Turn off "isochronous mode" if it is on. Set the same droop on each generator or they will not share load changes properly.

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

 

[gokmen]

Good Morning. Thank you nawao and waross. I will apply your suggestions during the first generator operation. But I still have a question mark. Is G1 speed increase normal, especiallly while its droop at 1% and no load change on the busbar? My point is the theory of operation. Many thanks again.

 

[itsmoked]

If I understand your statement you're not actually getting synchronizations as these two varying speeds never safely match.

The two not paralleled should have no relation to each other.

Does this mean that that one generator running by itself will also incorrectly speed up too?

It should not be dong that in iso or droop mode! I'd say there is a governor or control "problem", not just a "setting" issue.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[gokmen]

Itsmoked, yes they never match and synchronoskop leds keep turning CCW. When they work stand alone or after manual syncronization speeds remains constant, this makes me think I have problem with the RG491. At the other hand, why RG491 should send speed correction to G1 during the synchro period (before G2 connects to the busbar). Have you guys ever used or adjusted RG491 ?

 

[nawao]

For a correct synchronisation synchronoscop leds should turn CW. You can also try to set G1 in isoch at 1500 rpm and G2 on droop at 3%, speed lightly above 1500 rpm. In isoch mode G1 must not vary its speed; different behaviour could mean an installation problem.

 

[gokmen]

Ok. I scheduled the test to Saturday. I will try this setting also .

 

[waross]

I'll sit this out until after your weekend testing.

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

 

[gokmen]

Well, the generator control system is very old and we had too many troubles during the adjustemnts. We had to replace some bad relays which controls the ATSs in the synchronisation panel and this forced us to work 10 hours. I did try this adjusments;
1- G1:1500rpm, 2%droop and G2:1510rpm, 2%droop
2- G2:1500rpm, 1%droop and G2:1510rpm, 3%droop
The problem was still there for both of the settings.
I could not try isoc operation of G1.

I will focus on RG491 which has certain percent control of the governors. Thanks for advices again, still open for your advices.

 

[gokmen]

Well, problem was resolved .
1. There was some bad timing relays in the control panels. I have replaced them.
2. I made this adjustments on the governors : 1515 rpm 2%droop gor G1 and 1530 rpm 2% droop for G2.
3. I have adjust the RG491 cards's freq. pots (these are governors remote pots which has control of 10% of governor speed setting) and power balance pots to middle position.
4. I did simulate a power outage and saw that the G1 connected to busbar as soon as it reached to 90% of rated speed while G2 speeding down. I have decreased the G1's remote speed pot (on RG491) counterclokwise and maintain a steady speed at 50.6Hz. Then waited G2 to synchronize. After synchronization i watched the load balance. I did increase G2's speed from remote pot untill the loads on bots sets are aqual. I have watch the parallel work for 30 mins. During this time i did put and remove some loads on the busbar, the equal load sharing automatically maintained. I turned off both of them and simulate another power outage. Everything was good and satisfactory except the long synchronization time. It takes about 2 mins. It is good for now but later i will work on shorten synchronization time by decreasing G2's governor speed ( this is what i think related with ). Thank again friends.