Category: PRI Excerpts From The Metering
Essentials Handbook An Introduction To Metering Basics
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PRI
Introduction - The Metering Essentials Handbook - An
Introduction to Metering Basics
The booklet is designed to be a basic introduction to
the subject of electricity sub-metering and not a definitive guide to
installing any specific meter.
Tenant Billing Meters - Your Responsibilities
This is a subject that seems to cause a great deal of
confusion but the position is clear. In accordance with Schedule 7 of
the 1989 Electricity Act, any reading used to bill a customer or tenant
must be taken from a meter approved by Ofgem.
According to Ofgem:
“In the commercial environment, the landlord may take
a supply as a customer of an electricity supplier. Where the landlord
installs a sub-meter for re-supply to his tenants, he becomes the
authorised electricity supplier under Schedule 7(1)(10) of the
Electricity Act. He is authorised by exemption (Class B: Resale –
schedule 4 of the exemptions order, SI 3270/2001) and his tenants become
his customers. Generally, no meter shall be used for
ascertaining the quantity of electricity supplied by an authorised
supplier to a customer unless the meter is
a - of an approved pattern or construction & is installed in an approved
manner according to the regulations; &
b - is certified by a meter examiner or other person authorised to
certify meters” The landlord can be exempt from b. -
the requirement for certification - if the landlord has agreement in
writing with his tenant before the meter is used (Schedule 7(2)(2)).
However, there is no exemption for a. as “It is an offence for an
authorised supplier to supply electricity through a meter that is not of
an approved pattern”. What are the Implications?
This rules out almost all panel mounted sub-meters as
very few have been approved.
How can you be sure a meter is approved? You need to
be careful here because it is not unknown for some suppliers to claim
approval when they don’t have it. The simple way you can be sure is to
ask for a copy of their “Certificate of Approval”.
CoP5 Meters (Code of Practice 5)
All sites rated above 100kW but below 1MW will have a
CoP5 meter installed for billing purposes. These are special meters that
record and store 30 minute load survey data. This data is collected
daily via a communications link by an approved data collector. The data
is then used to create the customer bill and the charges the electricity
suppliers have to pay for using the network to deliver the electricity.
The data is owned by the supply company but the customer has the right
to access and collect the data at no additional cost (some supply
companies charge to provide the data in a convenient format). To access
the data directly your Meter Operator will need to put a customer
password into the meter and you will need agreement from your supplier.
The meter manufacturer or a third-party will be able to supply suitable
software to access the data but note that you are only allowed to
collect the data between midday and midnight as the rest of the day is
reserved for data collection for billing and settlement purposes.
Above 1MW CoP3 meters are used and these operate in a
very similar way to CoP5 meters. Elements of
Sub-metering
The term ‘secondary’ or ‘sub-meter’ usually refers to
commercial or industrial applications downstream of the main billing
meter. Safety
Because of the dangerous voltages involved any
invasive work must only be carried out by suitably qualified staff or
contractors in accordance with current health and safety regulations.
Wiring Regulations
BS7671 came into force on 1st April 2006 and covers
harmonised colours and alphanumeric marking of cables, conductors and
terminals in new electrical installations. It is now not permissible to
install equipment or wiring in the UK using the ‘old’ colours (red,
yellow & blue for phases, black for neutral). All conductors and
terminals must be marked ‘L1’, ‘L2’, and ‘L3’. Conductors can be
colour-coded either with ‘new’ colours (brown, black & grey for phases,
blue for neutral), or brown for all phases, blue for neutral.
Types, Characteristics & Applications
There are three main designs of fixed electricity
meter: surface-mounted for fixing to a wall or on the front of an
enclosure, panel-mounted for installing in the front of an electrical
panel and DIN-rail-mounted for mounting in the back of a control panel.
In addition to the mounting format, meters may have differing
characteristics, according to the application: Basic –
kWh meter with display and kWh pulse output, used on switchgear for
outgoing supplies and for connection to a monitoring system. Used widely
for compliance with Building Regulations L2.
Multi-function – Multi-parameter meter with pulsed
outputs and a range of communication options. Often used on the incoming
supply to switchgear to provide additional information for the
electrical engineer. This type of meter can be connected to a
power-monitoring or energy-monitoring system.
Power Quality – These specialised meters are used to
capture transient events and identify problems such as harmonics.
Load Profile – These meters store half-hourly load survey data for local
or remote collection. Some have the ability to accept pulsed inputs from
other devices such as gas and water and can be the basis of a very
cost-effective monitoring system. Web-enabled – Yes,
it had to happen; meters with built in web servers that can be read via
your data network or via the internet using a standard browser.
Accuracy & Standards
Class 1 accuracy is usually all that is required for
sub-metering applications. Select a meter that meets a good
international standard such as IEC/BS EN 61036 but more importantly buy
your meter from a reputable manufacturer or supplier that can provide
after-sales support for the life of the meter.
For power quality meters use the international
standard EN50160.
Communication Options
Pulsed Output – As a minimum the meter should have a
kWh pulsed output. Meters that also offer a second output for kVAh or
kvarh will allow power factor and kVA or kvar Maximum Demand to be
monitored.
Pulse counting is relatively crude and long-term
accuracy from a remote monitoring system cannot be guaranteed.
Analogue Signals – These signals can be fed into SCADA systems for
continuous monitoring of voltage and current etc.
Serial – Here data is passed from the meter to a PC
in response to a question.
This type of communications is superior to pulses
because the data is authenticated meaning the reading from the
monitoring system will always match the meter. Serial
Bus – RS485 Modbus is a very common, low cost way of communicating with
a large number of meters over long distances.
Electrical Connections
The majority of sub meters sold in the UK are 230V,
3-phase, 4-wire, connected via current transformers for circuits above
100 A rating. In this configuration of three phases and a neutral, three
CTs are required, one for each phase. If the meter has internal CTs the
secondary lead from each CT can be commoned and earthed, reducing the
amount of cabling needed. Not all low-voltage
three-phase supplies have a neutral. Systems such as 400V 3-phase 3-wire
motor controllers require only two CTs for accurate measurement.
High-voltage systems are also 3-phase 3-wire but voltage transformers
are used in addition to the current transformers, voltage transformers
are used to reduce the voltage to 110V.
Most industrial HV applications are 11kV although
other voltages (33kV, 66kV etc) are still used on some sites.
Building Regulations L2
These new regulations came into effect in 2002 and
are intended to improve the monitoring of energy consumption within
buildings with a view to reducing carbon emissions. The regulations
relate to new buildings or major refurbishment.
Section 3.4 states “Reasonable provision would be to enable at least 90%
of the estimated annual energy consumption of each fuel to be accounted
for.” An appropriate metering strategy needs to be put
in place and detailed in the building log book. Guidance regarding an
“appropriate meter scheme” is provided as shown below.
Separate metering is required for each of the following:
-
Each separate building or tenanted areas over
500m2 (Please note if the tenant meter is also to be used to
generate the bill, an Ofgem approved meter must be used)
-
Boilers / CHP plant 50kW & above
-
Chillers 20 kW & above
-
Electric humidifiers 10 kW & above
-
Motor Control Centres, pumps & fans above 10 kW
-
Electrical distribution boards, circuits above 50
kW
-
Any process load that is to be excluded from the
benchmarking process
All three phase supplies of 75A and above will need
to be metered. For single phase supplies the current rating will need to
be above 200A before metering is needed unless the supply is for
chillers or pumps etc as detailed above.
Energy Performance of Buildings Directive (EPBD)
The European Union Energy Performance of Buildings
Directive was published in the Official Journal on the 4th January 2003.
The overall objective of the Directive is to:
'Promote the improvement of energy performance of buildings within the
Community taking into account outdoor climatic and local conditions, as
well as indoor climate requirements and cost-effectiveness'.
Each EU member state is required to transpose the Directive into law by
the beginning of 2006 with a further three years being allowed for full
implementation of specific articles. Enhanced Capital
Allowances (ECA)
As part of the Government’s commitment to reducing
CO2 emissions, businesses investing in certain energy-saving
technologies can benefit from a significant tax break (100% first year
capital allowance). For further information visit the ECA website at
www.eca.gov.uk Carbon Reduction Commitment (CRC)
The Carbon Reduction Commitment Scheme (CRC) will
apply mandatory emissions trading to cut carbon emissions from large
commercial and public sector organisations, covering 10% of UK energy
users. Starting in January 2010, it covers organisations whose annual
half-hourly metered electricity use, and 70 kilowatt metered electricity
use in Northern Ireland, is above 6,000 MWh. Visit www.defra.gov.uk for
more information.
Other Sections Covered Include:
-
Meter Accessories
Current Transformers
Current Transformer Types
Accuracy & Burden
Summation CT’s
Conversion Plates
Fuses & Links
Meter Boxes
Meter Panels
-
Meter Installation
Common installation faults
Less common installation faults
-
Specifying Sub Metering
Accuracy, Approval, fuse/isolation maintenance,
distribution/availability
-
Specifying PRI Meters
Offgem Tenant meters, Sub metering, Load profiling, Web monitoring
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Excerpts From The Metering Essentials Handbook An Introduction To
Metering Basics
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