Parallelling Remote Generators 1

[EEJaime]

Gentlemen,

I have a situation wherein I will be parallelling two 1500kW generators to feed the Emergency Power system at an airport terminal. The problem is that due to space and security issues, the client wants to locate the parallelling switchgear inside the building and the two generators outside in a secured yard. The distance is approximately 150' between the two areas.

Can any of you see problems with this installation? I normally like to locate these adjacent each other for maintenance and testing issues.

Do you see any Code/Safety/Operational/Synchronisation or other technical problems with this? I can't think of anything other than the testing issue.
Thank you and regards,
Jim Murillo

 

[ScottyUK]

I don't forsee any technical problem with synchronising. If the generator doesn't have a local breaker then it's worth extending the diff scheme protecting the generator to include the cable. Pay extra attention to the grounding arrangements.

Can't comment on US code issues.


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If we learn from our mistakes I'm getting a great education!

 

[BigIanH]

I would agree with Scotty, but would always recommend a "local" breaker for isolation as well as protection.

Not that 150' is a huge distance, but you may want to take the generator voltage sensing point from the actual synch breaker rather than from the alternator.

 

[38ChevyGuy]

We have a number of installations like this, and although one would like everything to be together, there is certainly nothing wrong with it. Just be sure to run the power and control cables in concrete encased duct bank, for physical protection.

 

[ScottyUK]

I agree that sensing at the breaker is a good idea: it will help the AVR maintain a more constant voltage at the bus. Downside with having a second breaker in series is trying to get the protection to coordinate. Provided there is a good "lock out, tag out" procedure in place I have no problem working with a remote breaker providing the isolation point. On big utility class machines it is inevitable that this will be the case.


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If we learn from our mistakes I'm getting a great education!

 

[EEJaime]

Excellent points gentlemen, Thank you.
EEJaime

 

[FreddyNurk]

To add to ScottyUK's comments regarding coordination of protection, if you must do it that way with two breakers, be very sure of all the monitoring points, both for paralleling and mains failure (as I assume the application is). Coordination of breakers so that their status is always known is critical, else you can end up with systems 'seeing' a dead bus somewhere it isn't, or vice versa.

Also, in my experience, the switchgear is often better placed inside a clean air conditioned room, rather than mounted on the generator where its subjected to vibration and dust. Again, as ScottyUK has said, a proper 'lock out, tag out' system takes care of some of the issues involved regarding remote switchgear.

 

[Rodmcm]

There is no reason why you cannot have a simple breaker with overcurrent protection at the generator to protect the cables and the synch breaker inside. Another option is a simple breaker inside and the synch breaker at the generator which is my preferred option for smaller generators as the complete synch controls can be included on the generator. If it is MV though extending the protection around the generator is a cheaper option.

 

[alehman]

I've also used a fused switch at the generator in this scenario. Include it in the differential zone.

Alan
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"It’s always fun to do the impossible." - Walt Disney

 

[ScottyUK]

Re. last two posts:

If you do either of these things then pay very close attention to the interlocking between the local switch or breaker and the synchronising gear. Fit blown fuse indicators and tie them into the synchroniser logic too. If carefully designed then it will be benign enough, but there's definitely scope for an out-of-sync breaker closure if you aren't careful. I know procedure should prevent anyone operating the breaker while the set is running, but the hazard is better engineered out completely than proceduralised. I would definitely not want to be inside the generator enclosure during a bad sync: bits of con-rod bursting out of the block ain't funny when you are standing next to it.


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If we learn from our mistakes I'm getting a great education!

 

[EEJaime]

Next to it? I wouldn't want to be anywhere near! Thank you all for your very informative options. I think I like the non-intelligent breaker at the unit with the sync breaker in the parallelling switchgear indoors with proper lock-out hardware and procedures.

Thank you all again,
EEJaime