parallel utility for load bank 5

[ronnied]

I am working on an upgrade to sync 3 generators 2000kw each to an incoming utility with 4 feeders 4160v, the current system is not sync'd, and I want to use the utility instead of loadbanks for testing, can anyone tell me what will be needed?

 

[waross]

Synchronising experiences.
I found a situation in a small plant where the syncroscope was connected wrong. They used one 'scope and a selector switch for all 5 sets. The plant had two 600 kw sets and three 350 kw sets. For years they had been synchronizing at 30 deg. off true syncronism. I fixed it without measuring voltages but I estimated that there may have been 200 volts out of 480 volts across the breaker every time they synchronised. (Can you double check my estimate, please Gunnar? Thanks) The tip off was that after synchronizing, the synchroscope would snap to a position about 30 deg. off synchronism instead of pointing straight up.
A couple of years later an operator closed a breaker badly out of sync. and blew the coupling off a two bearing 350 kw generator. (All diesel, 1200 RPM).
respectfully

 

[ronnied]

Thanks for the details on paralleling, and how to use the plant rather than the utility for the loadbank, I will need to work on isolating load and not shutting down plant. As for the advise to find an expert, I did when I found you guys, and that will be me when I complete this project.

 

[itsmoked]

Thanks rbulsara.

Yes davidbeach; I recognize the need to twice drop some part of the plant. ronnied has never described what kind of plant he actually has but my thinking was if it is a 6MW plant he "might" be able to find 1.5-2MW that can tolerate two 10-20 second blinks per three generator load tests and get his full money's worth for his power generation,(which I suspect is his over riding desire[since he doesn't want to utilize the dumpster method]). Meanwhile avoiding the entire utility hassle.

Perhaps he has a 1MW motor and a large light load that can be dropped for the the switch over perhaps the load testing could start at 5AM and end at 1AM?? Something that naturally falls out of the plants circadian operation.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rbulsara]

If closed transition is emplyoed loads will NOT be dropped during a test. That is the real advantage of a closed transiton!!

You still need utility co.'s approval but it is much easier to obtain.

 

[davidbeach]

rbulsara, I suppose you are talking about closed transition transfer switches; what you say is true, as far as it goes. Using transfer switches, of what ever type, the load available is the load available, it may not be enough to fully load the generators. If the generators are paralleled to the utility, they can produce what ever power level is desired. Also, paralleling the generators to the utility, they can be ramped up and ramped back down, no sudden loading and unloading as would happen with transfer switches, closed transition or otherwise. Going from utility to generator with a closed transition transfer switch would block load the generator and the load would see the transient response of the generator to that block loading. Going back to the utility, the generators would experience a full load rejection (yeah, it happens with all generators connected through transfer switches) which is not a great thing to do to a generator more times than necessary.

 

[ScottyUK]

waross,

30[°] off synch on a 480V system would give a voltage mismatch of 2 x 277 x (sin 15[°]) = 143V. How did they manage 30[°] out with a wiring error? Probably lucky they didn't snap the crankshaft!

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I don't suffer from insanity. I enjoy it...

 

[waross]

Hi ScottyUK
I don't remember exactly, but I think they were using 277/120 volt, star connected transformers for the generator sensing and a 480/120 volt delta connected transformer for the bus sensing. That or something similar. The syncroscope would snap to 11 o-clock when they closed the breaker and they had been using it that way for over 5 years. The part that really amazed me is that they managed to blow a coupling off a couple of years after I fixed it. You have to remember, plant operators are paid very little in the third world and have virtually no training. No electrical training at all and on the job training rebuilding the diesels.
Thanks
Respectfully

 

[rbulsara]

davidbeach:

Closed transition can and is also done using breakers and protective relays and a synchoronizer (same as requirements as required for paralleling with utiltiy for extended time). Differerence betn ATS and breaker system is you can stay in parallel for longer time (several seconds vs. few milliseconds for ATS) and transfers large loads softly.

All I was saying was, if the guy is going to expend money to installe paralleling controls only for using utility as load bank, he can use the same controls for using the plant for the load bank and utility co. will be more agreeable to it.

 

[rbulsara]

If you want to know my honest feeling, if this were in the USA and this is an existing plant, installing a load bank would be much more economical and headache-free than intalling paralleling controls.

If paralleling controls already exist or this is new installation, then it is a differerent story.

 

[waross]

The rental price of a dumpster and a sack of salt won't buy much control gear. A forklift or truck mounted crane to support and control the depth of the scrap iron electrodes is handy as well.
respectfully

 

[itsmoked]

Waross; You might want to add the price of pool toys.

I still do like the simplicity.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi Keith
I learned of the method years ago when we were bidding a supply and instal job for a big standby generator. Thw specs called for a load test. The Gen-set supplier said, "That's easy we always rent a big dumpster (30 or 40 cubic yards, whole truck size) and buy a sack of salt.
We didn't get that job but I have used the method a couple of times since. Once was to load up a new set in which the rings weren't seated properly and were pumping oil badly. A day or so boiling water and the rings wore in and no more problem. Another time a supplier of a 280 kw set threatened to void the warranty if we used the set on light load early in it's life.
The compromise was a week of serious loading prior to putting the set in service. We used 6 plastic 50 gal. barrels and boiled water for 5 days. We used old truck leaf springs for electrodes.
If I ever have to do it again I will get some pool toys for the pictures. Forget the price, I'll pay for the toys.
Respectfully

 

[Tford]

Hi Waross,

Do you have any pictures that you will share of any of your boiler projects?

Cheers

 

[waross]

Sorry Tford
I don't have any pictures. Before I started I didn't know how hot the water was going to get. I was actually surprised to find that the 50 gallon plastic barrels would hold up to the boiling water. One setup was a 280 KVA genset at 120/208. As I remembered I used 2 barrels per phase. I topped up the water in the barrels about 3 times a day, and in the morning there would only be about 18" or 20" of water in the barrels. I had an oil pumping problem with a new 120/240 volt 18 KVA set. That only used one barrel. I would put my truck spring electrodes in the water and put the clamp meter on one of the cables. Then I would add salt to the water until I got enough current. Fortunately I am not subject to OHSHA.
respectfully

 

[Tford]

Thanks Waross! Enjoyed your posts.