MV generator coordination

[lielec11]

I was tasked with providing proof of selective coordination for the NYC Advisory Board on a project involving MV generators. I have attached a portion of the single line diagram.

My (stupid) question is shouldn't the "future load" breakers set at 600AT be lower than the 400AT generator input breakers? Otherwise it seems the generator input relays might trip first isolating the gens?

Edit: Not sure why I have so many issues attaching or inserting image files, they always come in so small! How can I get the full size image?

To explain, the gen input breakers are on the bottom of the image which connect to a paralleling gear. The paralleling gear then feeds an MV switchgear with a main and "Future" load breakers.

 

[Ingenieur]

will both gens run simultaeously?

if so each will suppy 1/2 the fault current
so there 'effective' relative rating to the 600 is 800
the time settings are important too

 

[ron]

The oneline resolution is bad, so I can't figure out what is shown, but if the generators are paralleled, then each gen will only contribute a portion of the source current so you cannot coordinate an individual gen breaker with a load breaker.

We are in the process of voting out the Advisory Board so maybe wait until they go away, then you only have to show the Building Dept.

 

[lielec11]

See below for image re-sized

 

[kingpb]

First off, there is no such thing as a MV breaker (4160V) that are 600AF/400AT, or any other size given in AF/AT. 5KV class switchgear will have minimum size breakers capable of 1200A. The protection relays will need to be set based on a coordination study.

It looks as if 2 generators are permanently installed with ability to bring in a trailer mounted unit as a third. The sum total of all three units running in parallel is going to be less than 1200A. So, your gen paralleling bus and upstream devices appear to be sized properly. Although if the third unit may not actually be there, the fault current tripping may need to be considered on the two units in parallel. The current should still be well above the rated running, but typically in MV relays, (SEL) you will have multiple setting groups. This would be a good application for use; i.e. one unit running, two units running, or three units running.

The total "Future" loads need to be limited to whatever the EG can supply if that's what the EG's are intended for. You can have 3000A worth of load, but if EG's are supplying them you will need load shedding or EG's will go into load rejection.

There seems to be a lot of "Future" indicated, so without knowing the particulars of what is wanted or intended, it's difficult to say what the set-up should be.