Prevention of Generator Shutdown Due to Fault

Please explain how generation of 683kVA is supposed to support a load of 1025kVA.

the load is only reaching a peak demand of 350kv.. and only 2 units are being used in the operation for some time and then the other unit is turned on to make one unit rest. this is the cycle of the operation on our distribution system. only 2 units are generating at a time.

What is the nature of the fault?

for example a single line to ground fault, a double line to ground fault and a line to line fault, this makes the generator sets shutdown. is there a way to extinguish the fault without the fault current reaching the generator sets?

by the way during faults, our fuse cut outs are down. but still the the generatos sets shut down. is there any type of fuse links which are acting faster than type K of AB Chance?

Line to ground faults can be disconnected using residual current circuit breakers, which have been discussed in these columns any number of times before. Their job is to disconnect the fault when one occurs downstream of them, like any other protective device. With good system design, only the affected part of the system will shut off, leaving other users powered and the generators running.

A line-to-line fault is best cured by having overload circuit breakers, correctly sized and selected, that discriminate between the minimum current needed to disconnect the faulty circuit and the maximum current needed to trip the generation off. Once operated, the faulty circuit is disconnected safely leaving other users supplied with power and the generation still running.

It sounds as though investment in a system review and follow-up recommendations by a qualified Electrical Engineering Consultant locally would be money well spent. Basically, hire someone who can look at it and sort it.

thank you sir. actually, i have known this idea before but we can't still afford to provide such protection system.. in our urban areas, we provide such expensive protection system. but this problem we have is in our remote areas where power transformers are still not available to supply power.

i just wanted to know if there are better ways to suppress this problem or any how to prevent it with the use of less expensive protection such as fuse cut outs.

"Can't afford"?

Whatever happened to "can't afford not to"?

Then look at loss of revenue from customers due to faults, and the investment needed to avoid them. Go for cases that show an easy payback.

Not-for-profit doesn't mean no-investment.

Oops. Easy pay-back first. The initial savings made then pay for the longer-to-pay-back investments.

With investment money so cheap in these low-interest-rates times, generating business cases (pardon the pun) for investments is so easy.

You're assuming that the transformer load rating is the whole circuit load rating. Now it might be the actual anticipated total load. If it is then there's nothing that can be done. For whenever the total load gets connected, the generator protection system will hopefully prevent the generators from being damaged.

Now if the total load is actually less than the available power from this generator set then the circuit breakers (fuses) can be sized to be less than what the transformers can support (if full power was available). This way a real fault will have the breaker as the weakest link instead of the generator protection system.

Eh? That is the solution.

Indeed. Until the OP explained it no other question could be asked.

I feel the time taken by fuses to isolate will be too long and that might be causing the generators to trip due to overload before the fuse melts.

Shouldn't you go for the faster isolators - relay+ breakers?

i guess you were pointing out same idea as with sir PWSLACK. can there be any more unexpensive ideas?

Yeah, Sorry PWS, the credit goes to you. .

CR4, is a team effort, AP2!

What is the cost of not doing it (rhetorical question)?

On second thought -

You may have faults at generating station (and its wiring/ bus upto transformers)

Individual transformers

Single transmission line

Distribution points.

If it is anywhere in the transmission line, assuming it is not on ring loop, then how does it really matter whether your generator works or not?

Even in your single line-earth fault or line-line fault, you can not isolate the faulty phase and let other phase run in a 3 phase generator. So even if everything is protected by as I mentioned, your system can not be switched on till the fault is rectified.

If it is a ring loop of course then you should have sufficient number of breakers, strategically placed to isolate the faulty section. But then I am not sure about your configuration.

yes i guess thats it. finally..

i think we have a problem on fuse sizing. we have a coordinated fusing system but i guess its the fuse rating that we are having problem with

That's why a fresh pair of (qualified) eyes is needed.

One thing I didn't see is what form of protection is tripping the gen-sets. There may be an opportunity to make this relaying less sensitive to long distance faults by making sure that the relaying is properly tuned. If everything is ok then the next step is to consider the use of a distance relay, an inverse current vs time relay or a combination of both, the idea being to discriminate between a generator or close in bus fault. If this is too expensive then consider increasing the trip time delay or adding a simple time delay relay in the generator trip circuit (at the risk of not acting fast enough if there is a legitimate generator, transformer, or close-in fault).

If you can provide more info on what's tripping the generator it would help all of us see the true nature of your problem.

Good grief! That would be far too expensive!

I think we're on a chewing gum and a bit of string budget here. Any expense spared.

thank you sir for the comment. the genset shuts down during faults. its built in circuit breaker is enable during this condition. the circuit breaker is set to the full load rating of the generator

This is a protection and coordination problem. Your generator side protective devices must have a time discrimination in operation with respect to the load side protective device.

Though the transformer ratings are larger, than combined generator rating, there may not be any problem due to this.

Consider using relays instead of fuse. I am afraid, unlike relays fuse may not reset its operation.

you should provide single line protection drawing. after that only your question can be answered