Handbook of Electrical Installation Practice - BeKnowledge

32 Handbook of Electrical Installation Practice
hourly market meter provision is seen as a default function of the distributor, which
is to be responsible for supplying meters as at present unless the supplier advises
that he would take this on via his own meter operator. Meter reading and data processing
are currently carried out by the data collector; default meter reading is seen
as the responsibility of the supplier. Ex-PES MSPs exist which can cover the whole
range of services, but there are also some companies which operate in one or two
areas only; for example, meter reading companies. Figure 1.13 illustrates this new
structure. Some PESs sold their MSP businesses and there is likely to be future rationalisation
and consolidation.
Requirements for accuracy of metering
In UK legal metrology, product standards published by BSI are used as the basis
for approval by the Electricity Metering Examining Service and for accuracy levels
for certification testing. Meter standards relate to class, e.g. a Class 2 meter has a
reference accuracy of ±2%. Standards exist for Classes 0.2, 0.5, 1 and 2 meters, both
electromechanical and electronic.
So-called ‘whole current meters’ are suitable only for voltages at 400/230V and
currents of up to 100A. Instrument transformers are necessary to match base meters
to higher voltage and/or higher current supplies. Standards exist for various classes
of voltage and current transformers, which typically operate on secondary values of
110V and 5A respectively.
The metering equipment at customers’ premises was specified in national Codes
of Practice at privatisation. That for supplies of 1MW and above required fourquadrant
metering to Class 0.5 accuracy (Class 0.2 above 10MW). The Code for
100kW metering equipment reduced the requirements to Class 2 accuracy, measuring
only import active and lagging reactive energy. The code and the agreed procedures
are still relevant and now form part of the NETA Balancing and Settlement
Code.