Generator Paralelling

[joan271273]

Does anyone have experience with paralelling a Cummins 1500 KW with a CAT of similar size and generator pitch.

The Cummins use the Power Commader PCC and the Cat has a Woodward governor.

Someone state that the use of Cummins ISLI card would make this paralelling achievable and glitch free, but other seem not to agree.

Help!!!

 

[peebee]

I don't have any experience with that specific application, but generally, I'd recommend picking one vendor and asking them to change out the controls on the other's generator so that both match.

 

[joan271273]

I am having problems with this approach as everyone is giving me a different picture ( ++$$$$). I am trying to educate myself a bit in this case to be sure I am not getting hosed

 

[RajT]

You should have absolutely no problem with paralleling the two sets as the governor and AVR characteristics of both the sets would be identicle irrespective of different makes.

 

[DougMSOE]

As a former operator of stationary and marine diesel/CT/GT I will offer this. As long as you have a synchro-scope or a 3 dark lamp system, you should be able to do this glitch-free, in manual. As a designer of these systems, some very simple auto sync chech/synchronizing/loading will get you there every time.
Slightly to the side of this discussion, I have seen in my 30+ years as an engineer too many people try to solve the problem with high tech stuff. I have no problem with this this as long as YOU understand how the tech stuff works, and in a pinch YOU could perform the same task that you want the tech stuff to do.
Nuf said!

 

[peterb]

As I understand it, the question really is how to ensure that the units operate together when paralleled. This is a function of the governer setup and SHOULD be no problem, assuming that the governers in question have the required features. For example, if you set both units to operate in droop mode, the droop setting will determine the load sharing. Or you could set one unit for kW control, etc.

Of course, you will also need to ensure that the AVRs are set to share reactive loading correctly.

 

[joan271273]

The generators are for standby purpose in a continous process facility.

One of the issues might be is that is that the CUMMINS units will be on site in a permanent way and the CAT is from a fleet of mobile type units.

 

[TheBlacksmith]

Put them both in droop, with the same droop percentage settings and they should parallel and share load fine. Different droop setting could cause the machine with less droop to hog the load and exceed its rating. If the CAt is a mobile, it would probably be easiest to adjust it to match the permanently installed unit.

Blacksmith

 

[60cps]

there is a little more info that you could provide to nail this down. you said the pitch of the generators is close..that isn't good enough. typically cummins generators are 2/3 pitch and cat are optimum pitch. this causes circulating current problems if the neutrals/ grounds are connected to a common point. the last ditch effort would be to float the cat neutral/ground or put a reactor in the line isolating the neutral/ground, ps you didn't say if this was delta or wye. get the serial number of the generator, call your local cat dealer and have him verify the pitch. second, the load share lines cannot be connected because cat uses 0 to 3 vac as their load share signal. cummins uses a 0 to 1 ma signal on their governor. the simple way to do this hookup would be to make sure the voltage droop is the same % on each regulator. than set the largest generator in isoc and the other in droop (governors. this will allow the isoc unit to be the base load unit and the droop generator will float with the load. oh yah, make sure your sync lights are wired correctly (if you have any)if the cat is a power module, there will be sync lights on the panel I think you might be in a bind from the beginning if you manual parallel because i think the power command controller does not have a manual parallel feature so the cat unit will have to parallel to the cummins unit. the neat thing about the isoc /droop setup is not having to worry about a load share gov. there are methods of isoc parallel but as an earlier responder said, it is $$$$$$ you have to convert one or the other load share sig. probably 10,000 or more depending on how much protective relaying you want.

 

[joan271273]

60cps

1.- The units are identical in pitch.
2.- They are both Y connection.
3.- I will look at the CAT panel.

Any idea about the ISLI card from Cummins , any experience.

 

[peterb]

One comment, 60cps -
The unit that is set for isochronous operation will be the one to take the load swings. The droop unit will supply constant load if the frequency stays constant - and the frequency is maintained by the isochronous unit.

 

[60cps]

no info on the isli card. peterb was correct on the speed droop gen being base load and the isoc taking the swing. sorry about that. let's go back to the original inquiry. why are you mixing two mfg. for this project? unless you are getting the cat unit at a fire sale price or the customer already owns the cat, i would suggest you, either way (spend the 10-20k for control compatability interfaces or look for a cheap cummins unit, there are gobs of them sitting out there NEW). don't mess with droop paralleling if you don't have to. if you can keep the system isoc all the way, you and your customer will be a lot happier. there is a tremendous difference between being able to DO something and doing it efficently, and operationally sound.

 

[peebee]

I agree heartily.