Handbook of Electrical Installation Practice - BeKnowledge

28 Handbook of Electrical Installation Practice
the unit protected circuits to act as a ring-buster and limit supply failure in the event
of a busbar fault.
CONSUMERS’ SUBSTATIONS
In order to control and transform an h.v. supply, the consumer needs one or more
substations. They have to be designed to meet the regulations which apply for the
particular location. Regulations cover such matters as fire protection, safety, means
of escape, etc. To ensure that these are complied with it is advisable to employ an
experienced consultant. The work of installing and maintaining h.v. equipment is a
specialist activity and DNOs are generally prepared to quote for such work.
The main consumer switchboard is fed by the local DNO through its service
circuit-breaker with associated metering. At first sight it sounds attractive to use a
composite DNO/consumers’ switchboard, but taking all things into consideration it
is probably better to have the local DNO’s switchgear in a separate switchroom.
The single switchboard poses problems of meeting both specifications and of agreeing
the supplier. There are problems of authorisation of entry and of keys and security
locking. By providing an intervening brick wall and a short through-connection
the problem of co-ordination is much reduced and the cost is recovered in terms of
reduced overheads and a faster completion.
The consumer needs to have some of his staff authorised to operate the h.v. gear
and for this they require training. Depending on the equipment and layout it may
be appropriate for this to be done by the plant manufacturers but it may also be
appropriate for some training in safety procedures to be given by the local DNO.
Many have training establishments for their own staff and they may be prepared to
give the required training for an appropriate fee.
H.V. OR L.V. SUPPLY?
The local DNO generally charges slightly less for supplies at h.v. than at l.v., the difference
being determined by what it estimates to be the extra cost of transforming
and distributing the l.v. Providing all the supply is to be transformed to l.v. at a point
where the local DNO could equally well do it with its standard range of equipment,
then it probably pays to take a supply at l.v., since the local DNO has the advantage
of economy of scale in its activities and can exchange plant to match the load
most economically. Where economies can be made by deploying transformers
around the site or by using equipment at a higher voltage, this will tip the balance
in favour of the use of h.v.
METERING
Metering of bulk supplies
Metered values of supplies generated (by generating set) are summated and aggregated
as to each generating company. Supplies taken by suppliers are likewise