Synchronizing Cummins-Onan and Caterpillar Units

[joan271273]

I have a set of three (3) 1,275 kW Cummins Onan Stand By Gen Sets that will need to be able to work ( synchronize,share load,etc ) with three (3) trailer mounted Caterpillar Standby gen sets of similar size.

Now according to the engineer working On SITE this is not possible per the vendors and has not be accomplished anywhere else.

The site was purchased with Cummins units but the company back up fleet uses Caterpillar units.

Any knowledge on this.

 

[Juzu]

In principle there should be no problem if the units have governors than can be programed to work in paralel mode (non isochronous). Then yuo have to adjust the "drop"of the units to share the load.

 

[meihm]

Matching Alternator Pitch?

 

[alehman]

Newer Cummins generator sets configured for parallel opeartion typically use a proprietary electronic control system they call PowerCommand. Most of the "intelligence" is integrated into the proprietary contoller on each genset. The PowerCommand system controls synchronizing, generator circuit breaker operation, and load sharing.

Caterpillar on the other hand normally provides basic speed control and voltage regulators only. Synchronizing is performed by separate controls typically installed in the paralleling switchgear. This is the more "standard" arrangement.

I've never seen it done, but I've been told by Cummins engineers that the PowerCommand controller can be "dumbed down" to operate in a mode compatible with Cat and other 3rd party switchgear suppliers. You will need to get Cummins, Cat and your switchgear supplier coordinated, but it should be doable.

 

[ravi2002]

I agree with both of the above comments. But in spite of the intelligent controllers, and presently we are using advanced load controllers of digitised versions, and from my commissioning experience, please try the following:

First try to reduce the load connected to these generator sets to about 50~60% that too should be gradually increased later.

Manually try them in droop mode. Definitely should work. If there is fluctuation, try to adjust the gain (inside the controllers, I think should be PID loop, or PI loop)"K" of thr frequency control and voltage control. Some how, the first step is to run them manually, before setting it to automatic mode. (The PID setting adjustment has few methods, but try the trial and error method, starting with "P" first, then add "I" next, and if required add "D&quot

Further to remind you that in modern controlers, manual mode is always droop curve mode. automatic mode could be isochronous or droop depending on your setting.

Once parallel, increase the load and check stability. If you can take the reading of KW and KVAR of each unit, to identify the problem in frequency control or voltage control.

Hope it is of some help to you.

Good luck!

 

[Juzu]

If you have a Power Command Control system, there is no doubt that it is possible to put the Cummnis genset in parallel with other units. I have been project manager of a proyect in wich first one Cummnis unit was put into paralle with 3 other machines of different sizes and brands and 5 months later we put one more unit in parallel.

 

[genRman]

Joan271273,
meihem makes a good if brief comment.
I would suggest the correct method to use for investigating the possibilites of paralleling different types of genset would be to refer to the manufacturer of each genset, quoting type, serial number of the genset and the generator.
to my knowledge, Cummins / onan sets have (for the most part) generators with a 2/3rds pitch winding, where as caterpiller sets using, for example, marathon generators may a 5/6ths pitch winding.
In this case ( or any other where different winding pitches are expected to be paralleled) it is important to understand :
1. if generator neutrals are going to be interconnected
2. if each generator is provided with a full phase rated neutral
3. will you need a neutral current limiting device, such as a wound ferrite core choke assembly fitted to either of the dissimilar generators.

Failure to take the aproriate steps could result in a high level of circulating neutral current between dissimilar pitch generators.

If the genset people don't know, get the details of the generator manufacturer & call them direct, applications departments worth their salt usually hold an array of good, useful data, and coupled with the experience of an applications Engineer, can lead to problem less parallel operation.

 

[joan271273]

Thanks for the great input. Can you provide soem clarifications:

ALEHMAN: What do you mean by "dumbed down".
JUZU: What particular steps did you take in your case, or what were the main issues that you had to oevrcome.
GENRMAN: Do you have some sample calcs for these , or a web site that explains these a bit.

 

[PAFred]

This can be done how ever I would recommend using a droop type system rather than isochronis. That is providing that all of the gen sets are of the same pitch winding else you would really need to use a transformer between the different systems to simplify things although this would cost you some bucks!