Generator Breaker Selection

I was not aware that only highly professional questions will be answered and me as a starter in this area might come up with such simple questions if I came across a problem and I have seen ur this type of 'homework question reply' in so many comments. So pls if u r genious in this field don't hurt others attitude for learning thr' such sites.U can see students around u surfg for timepass, dont hurt anyone with such repies.

It is not about being a genius, it is about making sure that the right information is given out to right people for the right reasons. CR4 has been getting a few posted questions lately that appear to be coming from poorly-trained consultants or designers who are trying to use CR4 as a source of design information for commercial and industrial sites such as power stations and buildings. As you can imagine this is not acceptable and has the potential to put a great many peoples lives at risk, nor is asking the answers to homework questions. As your question looked like one of the above it was answered as one of the above (others have just ignored the post rather than responding like I have).

If it was nether of the above (which appears to be the case), could you please provide some more information on why you are asking such a specific question? Are you starting work in a consultancy company and this is where these very specific details came from?

If you are wondering why I was so harsh, I work in this field and asking these questions is like asking "how to build a bomb".

As Iam a student I can't imagine competitions among consultants.

As part of my project I came across this, so I came to know about this site for my clarification. I came across two SC ratings 44KA and 63 KA for Generator breaker, to decide that I asked that question with no aim to misuse CR4.

Ok, lets simplify your original question so that the answer is clear. You have a generator and a transformer with a breaker between them. The generator can produce a certain maximum amount of current under a fault (the fault current rating of the generator). The transformer also has a maximum fault current rating, along with an impedance due to its construction, winding configuration, etc. The fault Voltage is ignored as you are interested only in the fault current, the fault duration is also ignored at this time for simplicity.

The main points are "which way will the current flow in the event of a fault?" and "where will the fault most likely occur to cause the current to flow?"

The quick and simple answer is that the generator will produce the current, which will flow thru the breaker towards the transformer. The most likely points a fault could occur are AFTER the breaker, either due to a short circuit or similar on the primary winding of the transformer (giving you the worst case fault), or on the secondary side of the transformer (with the transformer impedance limiting the current). Faults on the wiring causing a short circuit are going to be less likely.

What about a fault between the generator and the breaker? In this case the fault current could flow back thru the breaker (by being supplied by the transformer in reverse), however two important points mean you don't really need to worry about this case.

1) The current will be LOWER due to transformer impedance and the fact that the generator is also supplying most of the current into the fault (lower impedance path in parallel with the transformer path).

and

2) If this rather unfortunate incident occurs, you have far more important problems to worry about as your very large and expensive generator and cabling has likely destroyed itself (and likely a small area around it) due to excessive mechanical force on the windings (due to the fault current) and overheating).

Hope that gives you a clearer idea.