Mechanical repairs required to a 3 MW, 11 KV standby generator engine. Then
genset also operates on a triad system.
The control side will be isolated to ensure that the prime mover does not
start during repairs.
Is there a need for electrical isolation of the HV alternator & busbar
breaker during repairs? No work will be carried out on the electrical side.
Not qiute the right group, but before working on HV equipment I would be
looking for a permit to work and proof of isolation from all poits of
supply. If you do not know this then maybe you should not be working on the
Yes! Accidents, when they happen, occur not because one thing went wrong
but because two or three things went wrong. It might be a change of
staff, a fitter or engineer who says 'Whilst we've got it out of
service.....', or even a moment of complete idiocy on the part of the
person doing the work. Like it not, it does happen, and the very first
thing the HSE will look at is the procedures in place.
I'd go so far as to consider some form of permit to work on the set.
Something that specifies how the set is isolated, how it is inhibited
from start up in the event of a mains failure during the works, and most
importantly, specifying the *exact* limits of the work.
Isolating the control side alone is totally inadequate. To prevent the
possibility of the unit motoring, you need to be absolutely certain
that there is no possibility of the unit becoming energised. You should
wind out the breaker unit, lock it out and lodge the keys with a
To prevent any possibility of the unit being accidentally cranked over,
whatever method of providing the cranking power should be removed. If
air, remove a section of pipe, if battery (unlikely) remove the leads.
Again lodge these items with a responsible person.
Simply turning them off is not adequate, as they can just as easily be
turned back on.
You will also require suitable notices to be displayed on the equipment
where these isolations have taken place, indicating that it has been
disconnected and that the equipment is being worked on.
All of this needs to be carefully documented before you start and each
item ticked off as it is done and witnessed. I am surprised that there
is no 'permit to work' system in place, for such large and dangerous
Thanks guys for the replies. A detailed switching schedule will be prepared
before isolation. Breaker will be off & racked down. Isolation & earthing
It was the mechanical components I was querying as no work will be performed
on the electrical side. But this will still be isolated. Of course, safety
locks & caution signs will be placed where necessary.
In addition to the HV isolation & PT isolation, the compressor air line will
be removed, fuel line as well. Battery negative lead will be removed and LV
control panel isolated.
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