Generator circuit breaker

[AusLee]

Hi,

Can you please give me a concrete example how to set the currents and time delays on an air circuit breaker protecting a generator?

I know that when you have a cable, the "characteristic" is an inverse curve, but what does the "characteristic" of a generator look like?

Thanks.

 

[Zogzog]

All the info about your system needs to be known, I suggest you have a PE determine this for you.

 

[davidbeach]

The instruction manual for a good generator protection relay should be able to provide considerable guidance, but you still have to know a great deal about the machine.

 

[AusLee]

I have all the parameters:

T'd = 0.51404 s
T'd0 = 7.1960 s
T"d = 0.0118 s
T"d0 = 0.0145
Te = 0.2225
Ta = 0.0608

Instantaneous LLL fault: 23589 A
Instantaneous LL fault: 20718 A
Instantaneous LN fault: 29952 A (I thought LLL would be highest)

Rated current: 3615 A

 

[davidbeach]

Actually, you don't have all the parameters, and if you thought that LLL would be the highest fault current you probably don't understand generators all that well. I'd echo what Zogzog said and recommend that you have someone more familiar with generator protection assist.

 

[AusLee]

I have more parameters, which ones exactly do you want?

 

[davidbeach]

It doesn't matter, no one here will, nor should be trusted if they do, provide your settings; that's not the purpose of the site. Then there's the whole question of what the rest of the system looks like, settings wise, as seen from the generator. Beyond that, there are no right answers per se, plenty of wrong answers, and a bunch of different answers that are all acceptable. But none of it in a vacuum as it would be looking at just the generator. Find someone locally who can see the whole picture, which nobody here can, and who can provide guidance.

If you want to come back with specific questions, and lots of supporting material as to how you have approached the problem, I'm sure you can get plenty of discussion. At this point, though, the problem is too wide open to be meaningfully solved here.

 

[AusLee]

The application is straight forward: the building is isolated. There is no mains supply. The generator is the only supply. There is only one generator straight connected to the MDB.

 

[alehman]

The generator will have a damage curve and a fault decrement curve. You'll need to get both of those from the manufacturer. Then take a look at the IEEE Buff Book as a staring point on how to go about setting the breaker. There are lots of consideration and unfortunately there's not a simple answer.

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

 

[slavag]

Hi AusLee.
What Alehman said!!!!.
ONLY, ONLY generator mnf. can give you answer !!!!
It's really hard Q.
It's not only simple O/C 50,51 protection, probably you need also 51V protection.
Try ask generator mnf..
Good Luck.
Slava

 

[AusLee]

Hi alehman,

The manufacturer gave me the data in the PDF file attached to the following link:

http://files.engineering.com/getfil...4ddc-a333-d78d5ecfb3f7&file=GeneratorData.pdf

What should i look at?

Thank you.

 

[alehman]

I suggested you obtain the thermal damage curve and fault decrement curve. Neither of those are included.

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