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parallel utility for load bank
5

parallel utility for load bank

parallel utility for load bank

(OP)
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?

RE: parallel utility for load bank

The generator controls will need the capability of controlling the watts and vars out of the generator; machines intended only to supply standby load, whether paralleled with other standby generators or only stand alone, may not have this capability.

An autosynchronizer that can synchronize the group of generators to the utility.  Right now your installation is likely to have individual autosynchronizers that sync the second and third generators to the first generator, but without the capability of controlling the whole group.

Protection at the point of common coupling that meets the requirements of the serving utility.  Since that point of common coupling doesn't exist now, that protection is unlikely to exist.  IEEE 1547 applies in the US and probably Canada and would be a useful starting point elsewhere.  I not know what IEC standard(s) would be a starting point in that part of the world.

An interconnection agreement with the serving utility.  The agreement will include the protection requirements, but will have a number of other requirement that can vary from utility to utility and region to region.

RE: parallel utility for load bank

I am not sure what you mean by "Sync" Do you mean running in parallel or load sharing? Are you trying to improve load sharing on standby generators? What type of governors do you have?
To connect to the utility:
You will need a synchroscope to be able to synchronize with the utility. One synchroscope and a three way selector switch is the cheapest.
You will need a wattmeter on each generator to monitor the loading. This is probably included in the generator instrumentation.
You will need an ammeter on each generator to monitor the current. This is probably included in the generator instrumentation.
You will need a voltmeter on the mains and on each generator to set the voltage. This is probably included in the generator instrumentation.
YOU WILL NEED THE PERMISSION OF THE UTILITY.
The utility will probably have additional requirements.
When the utility turns you down;-
Consider a couple of dumpsters filled with salty water. Use leaf springs from a heavy truck for electrodes. Obtain the springs at the scrap yard. It's a very economical load bank for a one time use. Be prepared to use lots of water.
I've boiled a lot of water this way.
Note; If load sharing is a problem, the solution is often to sdjust the "Droop" characteristic of the governors. This can be donw one machine at a time. If these are standby sets and you can connect one at a time to the utility and call it peak sharing you can set the droop quite easily.
good luck
yours

RE: parallel utility for load bank

First thing needed is the utiltiy company's approval. Start there you will see how soon this idea comes to an end.

RE: parallel utility for load bank

(OP)
I hear a lot of people talk like the utility will not allow paralleling but at my company we have gotten approvals, but never used it. However, the people here believe too that the day we ask for it we will get "what did you say, or I can't hear you, or your are breaking up call back later, etc." Is that what you guys are saying?

RE: parallel utility for load bank

Hello ronnied
I agree, many companies are selling power to the utilities.
Getting permission may be fairly straightforward. That doesn't mean it will be fast or cheap.
Your proposal will most likely have to be evaluated.
The utility will have protection requirements to protect their system in the event of a fault. They will probably re-assess the available fault current levels in their system in the area that will be affected by the extra available current from your generator. The Utility will certainly demand that you install a protective  relay system and that won't be cheap.
The utility may well allow paralleling and backfeeding, but the conditions that must be met make it very unlikely that the utility will even consider it for a few hours or days of load testing.
Rent one or more 40 cubic yard dumpsters (The big ones, 20 feet long) buy a 50 lb. sack of salt and 10 rolls of "Duck" tape to seal the tailgate. Use scrap iron for electrodes.
Plan on having a hose for makeup water. you are going to be boiling a lot of water.
respectfully

RE: parallel utility for load bank

It all depends on the utility.  Some make it easy, other make it difficult.  If you have an interconnect agreement with your utility, go for it; if the agreement is in place and you comply with your requirements, they will not keep you from running in parallel.

RE: parallel utility for load bank

I have worked on many systems like you are describing, and placed many into service.  Other facilities could not succeed for the reasons already mentioned.  

One facility could not parallel with the utility because their circuit breaker closing device was too slow.  The generators would get out of synch in the 5-7 seconds it took the breaker poles to close after the the synchronizer sent the clsoe signal.  Replacing the breaker was too expensive so the project was abandoned.

Others failed because the cost of converting a transfer switch to a circuit breaker was too high.

At another facility the resulitng short circuit duty with both the utilty and the generators on line was greater than the equipment ratings, so the project was halted.

Another one paralleled fine, but the protection system coordination was lousy.  Relays and fuses that coordinated well with current flow in one direction did not coordinate at all with power flow the other way.

Two other systems paralleled OK with the uility at 4160 kV with no problem until a ground fault occurred.  The wye-wye step up transformers and solidly grounded generators caused selectivity problems and dumped the hospital for every minor utility system fault.  Another one tripped the emergency room feeders due to circulating neutral currents between the utility transformer and the generator.

One new plant paralleled fine through the A bus several times, then blew the gear apart when they tried to synch to the "B" bus through the tie breaker.  A phasing problem  in the controls and the "B" transformer was not picked up by the engineer. (We were called in after the smoke was let out.)

So - talk to the utility, check your generator controls, check the short circuit ratings, do a load flow study, check the protective relay settings and review them with the utility.  Then check it all again and hire a good startup and testing team to verify everything.

RE: parallel utility for load bank

(OP)
Can you explain how to do the procedures you have referenced and provide the Manufacturers part numbers for the components/equipment you recommend?    
The test procedure to use the utility load was to save money over buying load banks, so I can not use the salt water test, but it will be a good reference for another project.

RE: parallel utility for load bank

Selling power to the utility is different than using them as "Load Banks".

We do a lot of paralleling with the utitliy. But that is not what OP asked.

RE: parallel utility for load bank

While many of our members have first hand experience  paralleling with utilities, it is the utility who dictates the protection that is required. Then, there is a lot of engineering required to select, adjust and co-ordinate the various protection devices.
This is not something that you can safely or legally do without co-ordination with the power company.
The utility will notice and investigate if you try to sneak 3 two kilowatt loads onto the system.
yours

RE: parallel utility for load bank

2
Don't you hate when you do that waross?
I do it all the time.cry

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: parallel utility for load bank

Hi Keith
I should have finished my coffee before posting.
 I stand corrected. You can probably get away with sneaking 2 kilowatt loads on to the system indefinitely. Your 2 Megawatt loads most likely will be noticed.
respectfully

RE: parallel utility for load bank

(OP)
I guess I was unclear; I am not trying to get around the utility. The plant has failing loadbanks and are considering purchasing new, but someone said if we were paralleling with the utility we did not need to purchase the loadbanks just use the utility - is this islanding?
I was asking for more details of what to look for or ask for when talking to the manufacturers of the new components you all said I would need like the master sync, or autosync and 3way switch. Also, how can I perform task like short-circuit calcualtions, or protective relay coordination without an expensive program?
Finally, can anyone explain manual sync using the Operator Window technique and a sync check relay, it is supposed to be a dummyproof method to sync the gensets to each other and/or the utility, and how should that work with the gensets in a 2+1 configuration?

RE: parallel utility for load bank

1> If you are paralleling with the utility already, just open the governors up a little and you will back feed and load up the sets.
2> Synchronizing. The basic method is synchronizing lights. The next step is a synchroscope. This tells the operator whether the unit coming online is running fast or slow, and when the phase relationship is right for synchronizing. Both these methods check phase relationships only. It is the responsibility of the operator to check that the voltages are equal before closing. There are relays to completely automate this procedure and also check and adjust the voltages.
"Also, how can I perform task like short-circuit calcualtions, or protective relay coordination without an expensive program?" This is a little more than we may be able to teach you in this forum. Much of the shortcircuit calculations will be preformend by the utility engineers to determine how the added capacity will affect the utility system. If you are already paralleling, this will have already been done.
You need to talk to an expert.
The first experts will be the engineers at the utility. They will tell you what they require for protection. Then you will need an engineer to design and install the system.
I understand that you may be in a position such that you have to gather a lot of basic information and pricing before you can get authorization to spend any money. There are still experts available that will help you at no cost. They are called "Sales Reps."
First, talk to the utility, then, start looking for sales reps for information and pricing on the equipment.
A quick run through, you will need a breaker or contactor to connect the plant to the utility. You will need a breaker or contactor to connect the plant to the genset. This is fairly straight forward. Now if you close both breakers at the same time, you are paralleled.
When the plant was originally designed, short circuit calculations were done to ensure that all the breaker were selected and co-ordinated so that a serious short curcuit could be interupted without any of the breakers failing.
Now, if you add 6 megawatts of power to the system by paralleling, the available fault current increases for the system. The original calculations for both your plant and for neighboring industrial plants is no longer valid. This maens that with your generators on-line, a serious short circuit at another plant may result in a breaker exploding rather than interupting the current.
Among other things, the utility will now meter current in both directions.
Paralleling is done one step at a time. Once a set is paralleled with the system it is part of the system. Then the next set is paralleled with the system.
You don't parallel all three sets and then connect them as a group to the system. There is another recent thread where a gentleman is trying to do some tests with unloaded gensets in parallel. To find out why you don't want to parallel unloaded generators check out thread238-153502
I hope this helps
yours

RE: parallel utility for load bank

What you are talking about - "just" using the utility as a "loadbank" - will be at least as expensive (in my guesstimate) as buying one new load bank you share between the four units.

Assuming the utility allows it, it's likely that you'll have to present a grounded source to the utility (that means a wye-delta or some other grounding source for the high-side of your utility connection), that you'll need distance relays (not cheap), bus differential relays and many other protective functions for both the utility and your generators that you probably do not currently have, you may have ground-fault concerns, available fault-current concerns, you may need different utility and generator control switchgear, you'll need power-factor and generator loading controls, special synchronizing controls, probably a PLC or set of PLC's to control this whole deal, plus a whole new set of safeties designed to trip your plant and/or generators off line in case of a fault.

There are good reasons to go through all these steps, I would not think "load banking" would be one of them.  The cost is not justified.

RE: parallel utility for load bank

tommom, in general all good points except that it is highly unlikely that a distance relay would be required.  Utilities don't, in my experience, use distance on distribution circuits and IEEE 1547 does not require distance for an interconnect.

RE: parallel utility for load bank

Why can't you just use your "plant" as a load bank??  Find a reasonable chunk of your plant, something/area under 2000kW and isolate it.  Run it with one of your three generators then as time passes start the next generator, parallel them and drop the first.
    
Step through each one as needed.  This lets you get the full value for your electricity whereas the utility will probably discount what you send to them. You shouldn't need much else perhaps some work to properly section part of your plant.  You wouldn't need any permissions from the utility.

You could possibly use tommom's PLC suggestion to shut down the part of your plant briefly and bring it back up on the generator.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: parallel utility for load bank

A star for Keith (itsmoked).  duh, why did not I think of that?

Utiltiy co. is more likely to accept a closed trasition (soft) transfer than someone feeding back power to them at their convenience. And you need the same parallleing protective relaying, only slightly less complicated than runninng in parallel with utiltiy for extended time.




RE: parallel utility for load bank

The problem with using the plant as the load is the need to drop the plant twice, often unacceptable.  I fully understand the desire for using the utility as the load, the plant would actually supply at least the bulk of the load, if not all of it, but it is necessary to parallel to the utility to get to the plant load.  Having the ability to parallel to the utility also makes it possible to come back from a utility outage without the need for a second interruption (the first being when the utility dropped out); a parallelable system can also be smoothly moved from the utility to local generation as a storm avoidance measure.  All valid reasons to want to parallel, but the paralleling has to be done correctly.  This forum probably isn't the best place to learn how to do that however.  There have statements from ronnied that suggest he (she?) is getting in over his head and should really engage the services of a local consultant who understands the details of parallel operation with the utility and the requirements of the specific serving utility.

RE: parallel utility for load bank

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

RE: parallel utility for load bank

(OP)
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.  

RE: parallel utility for load bank

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

RE: parallel utility for load bank

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.

RE: parallel utility for load bank

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.

RE: parallel utility for load bank

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!

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

RE: parallel utility for load bank

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

RE: parallel utility for load bank

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.

RE: parallel utility for load bank

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.

RE: parallel utility for load bank

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

RE: parallel utility for load bank

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

I still do like the simplicity.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: parallel utility for load bank

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

RE: parallel utility for load bank

Hi Waross,

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

Cheers

RE: parallel utility for load bank

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

RE: parallel utility for load bank

Thanks Waross! Enjoyed your posts.

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