Generator EFLI values

Hi All,

Apologies if this has been answered previously & forgive me for my lack of knowledge on generators.. However we are currently involved in a project on a new school building that has a 275Kva backup generator. Due to delays with the DNO, The generator is likely to supply the building on a permanent basis until at least the end of the year. 

It's currently situated around 20 m from the building and we have parallel 95 m4 core SWAs from the generator to the ATS switch. 

We have a specialist earthing company coming in to give us an earth array for the generator & They seem to think they can give us around 1 ohm resistance. 

What i can't quite grasp, Is whether I'm right thinking that that one ohm value on the earth array has nothing to do with the loop Impedance we will be getting to the building as this Should solely be based on our L-E resistance back to the star point of the generator? 

If I am completely missing something & our Ze value at the building when fed via the generator will be 1ohm minimum, then we need to ensure correct final circuit protection (IE 30mA RCBOs) on the majority of final circuits that will exceed the maximum ZS values to meet disconnection times.

Any advice would be greatly appreciated.

Thanks,

Tim

Parents
  • A couple of things to think through.....

    Generators come in two flavours - 'prime' & 'standby' and as such have different ratings. A 'prime' set is capable of delivering its rated output full time. A 'standby' set is not - it will be rated for a number of hours. I suspect your set may be a standby rated one and will not be capable of delivering the power you expect full-time.

    Is this is intended to run 24/7 until the mains is connected ? What about servicing? It will need to be to be serviced approx once a month.

    Fuel will be a headache. If this generator is running at anything close to full load its going to be drinking close to 1 litre/min. ie. around 400 litres for a 8 hours day. Considering that red diesel cant be used to run gensets anymore & with the current cost of white diesel - somebody needs to be thinking in terms of £500+ per day for fuel......

Reply
  • A couple of things to think through.....

    Generators come in two flavours - 'prime' & 'standby' and as such have different ratings. A 'prime' set is capable of delivering its rated output full time. A 'standby' set is not - it will be rated for a number of hours. I suspect your set may be a standby rated one and will not be capable of delivering the power you expect full-time.

    Is this is intended to run 24/7 until the mains is connected ? What about servicing? It will need to be to be serviced approx once a month.

    Fuel will be a headache. If this generator is running at anything close to full load its going to be drinking close to 1 litre/min. ie. around 400 litres for a 8 hours day. Considering that red diesel cant be used to run gensets anymore & with the current cost of white diesel - somebody needs to be thinking in terms of £500+ per day for fuel......

Children
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