Synchronize Generators To Utility 4

[SyncCheck]

Hello all,

I need to synchronize 4 CAT C9 generators to a bus and then synchronize the bus to utility.

I am useing a Woodward SPMD synchronizer & load sharing module on each generator.

Now here is the part that I am haveing problems with
how do I synchronize the bus to utility?

I was thinking of useing an SPMD on the utility side and use the speed output from the utility SPMD and parallel it to all to the load share modules on each generator and then the generators would actively sync to utility.

Any ideas?

The transfer would be fast because all what I need to do is a bumpless transfer from generators to utility,(kind of like a closed transition transfer switch)

If you need any more info let me know.

Thanks for all the help

 

[waross]

The easiest way is to go to droop mode on the generators.
Why can't you sync the bus to the utility with one generator and then add the others?

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

 

[SyncCheck]

Hi Bill thanks for the reply,

The generators are for a hospital,when their is a black out the generators go online and synchronize together and pick up the load for the hospital.

The problem is when the utility is restored I need to transfer the hospital load from the generators to utility in a bumpless transfer.

I know that their are closed transition transfer switches out their, but thay just wait for the 2 sources to come in phase with each other and this can take minutes...

I need to actively synchronize the generators with utility so I can do a fast bumpless closed transition transfer and then shut down the generators.

Any ideas?

Thanks

 

[rbulsara]

Bill already gave you the idea, that is how it is normally done.

Besides that you will need permission from the utility company and if they do allow it, you will most likely need additional inter-tie protection (relays).



Rafiq Bulsara

http://www.srengineersct.com

 

[SyncCheck]

Already have permission from the utility company to synchronize and already have protective relays.

if thats how its normally done what are you going to do about the load, what if you cant bring the load down?

 

[catserveng]

Closed transition return to utility is normally limited to being paralleled less than one second, then tripping off the gens, as long as the utility supply is stable, you shouldn't have a problem.

Depending on your site and utility they may allow a longer return transition. Depending on the model of SPM-D you got, some have a load share feature. But since this is a hospital application, you may want to find someone in your area familiar with paralleling controls.

I've done a few systems where the local utility allowed us 2 minutes to ramp transition the site load back to the utility. But this system could also parallel to grid and export for demand response, so all the controls were in place for that as well.

You can also ask you local Woodward Rep, he may be able to tell you if your SPM-D's can have one across the main and sync the gens. The Woodward DSLC platform used an MSLC (Master), and the newer EasyGens can be configured for Mains breaker control.

Again, strongly urge you to get the right help, learning this while trying to do it for a hospital could be a rough road for lots of people, you included.

Hope that helps.

 

[waross]

Two questions here. One is picking up the load, the other is transferring back to the utility when utility power returns.
I don't see waiting for a minute or two for a sync to be an issue. If it is, tweak your frequency setting a little.
You may want to consider ramping your frequency setting or your throttle control down slowly after connecting to the utility. This will avoid dumping a block load on the utility.
Ideally, you would be a little above the utility frequency by a cycle or 1 1/2 cycles. When you want to transfer, start to ramp the throttles down and connect to the utility at about 1/2 cycle below the utility frequency. Keep ramping down the throttles until you have shed most of the load to the utility. Then open the generator breakers and let the engines run a few minutes to cool the turbos down before stopping.
I say throttles because that's the end result you want. You may do it be frequency adjustment or some other method.
With droop controls, you would ramp down the frequency settings. Not sure with a load control panel. Some other method may need to be used. Dropping the frequency setting on droop governors will first shed the load before actually dropping the frequency. If you drop the actual frequency with a load control panel, you may go into reverse power trips which will probably not make for a smooth transition.
Said another way; As you drop the frequency setting on a droop governor with 3% droop, the set will transfer load to the utility as the frequency drops and reach zero load at a setting of 58.2Hz. (60 Hz minus 3%x60 Hz.)
If a load control panel commands a frequency drop you may be immediately into reverse power mode.

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

 

[rmw]

I only ever put one hospital in the black. Of course I put the whole city where it was located in the black with it too when I tripped their larger generating plant (which took out the smaller generating plant). It is not a good feeling.

I wasn't too much worried about all the folks without air conditioning on a hot summer afternoon, but I still (that was 35 years ago) think about who might have been on the operating table at that moment on a hear/lung machine or something similar. I doubt that the hospital had back up power back then. Not a good feeling.

The city had a black start CT and soon got it on line but it took them the better part of an hour to do it (air starter on the diesel starter engine for the CT depended on plant air from the plant I had just tripped which was black with the rest of the (islanded) city. It took a sewer dept Smith 75 (cfm) compressor to do the trick of supplying the starting air and it took the sewer department the better part of an hour to get there with it. I still remember the sight of the sewer dept pickup truck coming through the gate of the plant with the compressor in tow and up on one wheel as it made the curve into the plant as if it were yesterday.

Not a good feeling.

rmw

 

[rbulsara]

synccheck:

If you already have a system and permission in place, I wonder what makes you ask this question? Are you at the commissioning stage of the system? or this system was already working and now you have a problem?

In either case you need to bring in someone intimately familiar with the system at the site, including the mfrs and also involve the design engineer.

What you want to do is routinely done, that does not mean it is done without experts involved. This is not something you want to do with remote general advice.





Rafiq Bulsara

http://www.srengineersct.com

 

[SyncCheck]

Rafiq, I am in the design stage right now and looking at what would be the best way to achieve this...

I am still looking at diffrent controllers to do the job easyer and use less of the PLC for control.

I will keep you all updated on my progress.

Thank you to every one on this form for your advice

 

[nawao]

Synchronising a group of generators back to the grid is not a good option.
I fully agree with above catserveng advice.
Since all sensitive equipment in a hospital must be supplied through UPS, why is needed a bumpless transfer?

 

[SyncCheck]

nawao,

Yes I have UPS systems all over the hospital and that is not the problem...

I just dont want to have the lights flicker nor do I want to dump and spike the power grid with a 1 MW load.

 

[davidbeach]

During start up, the gen bus is your reference for synchronizing; when you want to go back to the utility use the utility as your reference, switching with a multipole relay.

On the other hand, I wouldn't go back to the utility for 20-30 minutes so what does it matter if passive synchronization takes an extra couple of minutes?

 

[SyncCheck]

That is what I am trying to do,have the generators synchronize to utility and when the bus is on utility I trip the generator breakers and cool down.

The reason why I want to actively synchronize to utility is in the case of low fuel so I can quickly transfer and unload to utility...

I have synchronize generators before but never to utility,looking for a controller or a solid scheme on how to do this,I know about the dangers of synchronizing to utility so that is why I am triping the generator breakers after 100mS.

I am looking at some Woodward controllers and it looks like some of the controllers can do this but their is no good information on their web site.

Will try to get a manual or talk to some one at Woodward on Monday..thinking of useing the SPM-D 21 (2 breaker control)has any one worked with this?

Thanks

 

[catserveng]

The SPM family of controllers are pretty good, sometimes the setup can be a challenge.

However, the SPM series is designed to parallel a single unit across one or two breakers, and maybe do load share. What they don't do is to work with a master to bring a multiple generator generation bus in parallel with a utility. The workhorse system Woodward had was the DSLC/MSLC system, I have put a large number of these systems in and it will do what you want. Two problems, they are expensive and they are going out of production soon.

The GCP-30 controller has a version with CANBUS to do multiple unit communications, but this controller is also being replaced.

The easyGen system is the current offering and will do what you need, maybe still pricey, and will take a bit of work to get things tuned up to work properly for a multi unit paralleled standby system.

Many switchgear vendors offer their own system, usually PLC based, I tend to not like those type systems are you are pretty much stuck with having to use the switchgear companies rep to make any changes. Likely the CAT dealer you're buying the C9's from could offer you a CAT Switchgear solution, but personally I'm not a big fan of theirs either.

What are you doing for switchgear? I hope you're not considering the C9's with unit mounted breakers and doing some remote controls. Some folks tried that and it was cheap, but the breakers had early hour failures.

Also wondering why 4 C9's? Two C15's or a C32 would certainly make a less complex system, plus take up less space.

Hope that helps.

 

[davidbeach]

If you start the outage with 72 hours of fuel and refuel every 24-48 hours, how do you get to such a low fuel condition that 2-3 minutes will make any difference? If you can get into that condition you have far bigger worries to take care of than how to synchronize to the utility.

 

[SyncCheck]

Hi catserveng,

The reason of why I am useing 4 CAT C9 insted of 1 big generator is because this hospital use to be in 2 sections and now thay are merging and adding more sections and turning the hospital in to one big hospital,the existing stand by generators were CAT C9 and are fairly new and had specific locations in the hospital so just putting 1 big generator in was not an option.(I tryed to convince them on putting in a 1MW genset but thay did not want to rewire the power system)

All the generators have an on board GCB and I am not useing that,I am useing Cutler Hammer Magnum DS power breakers,I agree with you on the breakers thats the worse thing to do...

Would the easyGen controller be overkill? I am not trying to stay on the grid for long I just want to do an active closed transition so I can transfer load with out a blackout or bump, the genstes wont be on the grid for more then a few mS.

davidbeach,

All generators have 24HR day tanks ,I have sized the backup power system to have 150KW of reserve overload capability but if 1 genset was to go down I would have to load shed most of the HVAC MCC's because that exceeds the overload.I have all the generators alarm and low fuel relays comming back to the PLC so if the utility is on and I have an alarm I can do a fast transfer any thing else I give the utility 10 minutes to stabilize...

Thanks

 

[burnt2x]

David,
I really think your common sense is running perfectly well! A star for you!
SyncCheck,
Think out of the box and KISS it (Keep It Stupidly Simple)! Please make a good refuelling procedure and avoid getting your day tanks dry. No need to synch your units with the utility, IMO.

 

[catserveng]

If all you're trying to do is get back to utility fast there may some other options as others have discussed. Maybe a couple of other questions to ask.

Ever going to be a desire to get off the grid before an outage? Say in response to a high demand, looming weather or a utility problem? Sometimes having the option to get off the grid "bumpless" can drive your decision process.

What is the end users expectations of the emergency power system? Going to do it all in auto? Does it need or require plant staff to be involved for return to grid? How are determining the grid is stable and ok to return too?

More systems are going in the direction you are trying too, with paralleling of smaller units and ability to close to grid, but it comes with a price of higher complexity, different maintenance demands, and skill levels needed by plant operations staff. You also have to regularly test the entire system, not just the annual full load test on each gen set.

I'm still thinking you really need to find a local source of expertise in paralleling systems and get them directly involved if this is the path you want to go with.

 

[davidbeach]

I don't know where you are but only 24hr worth of fuel is probably a code violation and is certainly engineering malpractice. Last I checked (it's been several years since I was doing hospitals) 72 hours of fuel was the minimum requirement and I wouldn't be surprised if it has gone to 96. 24 hours is certainly no where near enough fuel. Solve the big problems before you worry about the minor details.