Handbook of Electrical Installation Practice - BeKnowledge

68 Handbook of Electrical Installation Practice
400V this would require two 4-core cables of 240mm 2 in parallel (assuming a
requirement for a neutral). The cost of 1000m of such cable would be in the region
of £14600. While in theory the same power could be conveyed at 11kV by a 3-core,
6mm 2 cable, in practice the smallest available cable for this voltage is likely to be
3-core, 25mm 2 . Nevertheless the cost of 500m of this cable would still only be in the
region of £3000. A transformer would be needed at the remote end and a 500kVA
oil-filled transformer would cost approximately £4700.The 11kV system would thus
show an approximate saving of almost £7000 over the 400V system for what is quite
a modest power distribution requirement. (These calculations are based on prices
at December 2001.)
INTAKE ARRANGEMENTS
While low voltage intake arrangements are generally simple single feeders there are
many possible configurations for the interface between the consumer and the DNO
on high voltage supplies. Some of the more common arrangements are described
below.
The exact point of demarcation between the consumer and the DNO should be
the subject of formal agreement. It becomes particularly important, and sometimes
contentious, in the event of faults and the allocation of repair costs and may sometimes
be pin-pointed down to the cable lugs and the bolts securing them inside a
cable box. The simplest arrangement is for a single transformer to be owned by the
consumer with the h.v. switchgear supplying it owned and operated by the DNO, as
shown in Fig. 3.1. This arrangement relieves the consumer of any high voltage
switching duties but makes him completely dependent on the DNO for making live
the transformer or isolating it for maintenance. (Facilities are usually provided to
Fig. 3.1 A single high voltage intake with h.v. switchgear under control of the DNO.