Produced by Alan Ward

Transcription

1 Produced by Alan Ward

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3 Contents Approved Billing Meters 5 Electricity Act 1989 Measuring Instruments Directive Code of Practice 5 (CoP5) Renewable Obligations Certificate (ROC) Metering Elements of Sub Metering 9 Safety Wiring Regulations Types, Characteristics and Applications Accuracy and Standards Communication Options Electrical Connections Building Regulations L2 Energy Performance of Buildings Directive (EPBD) Enhanced Capital Allowances (ECA) Meter Accessories 15 Current Transformers (CT) Current Transformer Types and Polarity Accuracy and Burden Summation Current Transformers Conversion Plates Fuses and Links Meter Boxes Multi-meter Panels Meter Installation 20 Safety Common Faults Less Common Faults Specifying Sub-meters 22 UMS Ltd Products and Services 23 Application Profiles 24 Useful Contacts and Links 25 3

4 Introduction This 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. All installation work should be carried out by a suitably qualified electrician who is fully conversant with the meter being installed and the latest wiring and safety regulations. If in doubt please contact the meter manufacturer before carrying out any work. 4

5 Approved Billing Meters Electricity Act 1989 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 of an approved pattern or design. This is a subject that seems to cause a great deal of confusion but according to Ofgem the position is clear: 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 and is installed in an approved manner according to the regulations; and 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 from his tenant before the meter is used (Schedule 7(2)(2). However, there is no exemption for a. the requirement for approved installation, as It is an offence for an authorised supplier to supply electricity through a meter that is not of an approved pattern. 5

6 Measuring Instruments Directive (MID) The European Measuring Instruments Directive came into force on the 30th of October MID is designed to create a single European market for approved meters so that a meter approved in one EU state can be used in any other EU state without any additional testing. What are the implications? 1. Ofgem is no longer the body responsible for approving meters for use in the UK. However, meters approved by Ofgem before MID can continue to be manufactured, verified and used for billing purposes. 2. Meters manufactured and approved for use in other EU member states can now be used in the UK without the additional need for Ofgem approval. The technical responsibility for managing the MID approval process has been transferred from Ofgem to the National Weights & Measures Laboratory (NWML). How can you be sure a meter is approved? Existing meters approved by Ofgem are listed in Schedule 4 and this can be downloaded from the Ofgem Website. Here you will find details of the manufacturer, meter designation and approval certification number. For meters approved under MID, the supplier will be able to provide details of the EU country where the meter was approved, the Nominated Body that carried out the approval and a certification/reference number confirming approval. 6

7 Code of Practice 5 (CoP5) Meters 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 load survey data every 30 minutes, i.e 48 readings per day. These readings are collected daily via a communications link by an approved data collector. The data is then used to create the customer bill and the charges that the electricity suppliers have to pay for using the network to deliver the electricity. Although data is owned by the supply company, customers have the right to access and collect the data at no additional cost. Data can only be collected by customers between midday an midnight as the rest of the day is reserved for collection by the data collector for the purposes of billing and settlement. For a customer to access the data directly, agreement from the supplier is required and your Meter Operator, responsible for installation and maintenance of the system, will need to put a customer password into the meter. The meter manufacturer or a third party will be able to supply suitable software to access and process the data. Some electricity companies will offer to provide the data in a convenient format for downloading from a website but may make a charge for this service. Above 1MW CoP3 meters are used and these operate in a very similar way to CoP5 meters. Further information on Code of Practice metering can be found on the Ofgem website. 7

8 ROC Metering ROC stands for Renewable Obligation Certificate and since April 2002 all licensed electricity suppliers have been required to source a proportion of their electricity from renewables. The proportion is variable and increasing year on year. ROCs are not just for utility companies, any organisation can register with Ofgem and if accredited can obtain ROCs. 1 ROC is awarded for every 1MWh of electricity generated and once obtained ROCs can be sold on. Ofgem requires that any meter used for determining the amount of renewable electricity generated must be of an approved type i.e. Ofgem or MID approved and be installed in an approved manner. Electricity used by the generating equipment, often called the parasitic load, is deemed as input electricity. Input electricity must be deducted from the output electricity as it does not qualify for ROCs. Approved metering must also be used for measuring input electricity and any electricity exported from the site will require appropriate balancing and settlement code compliant metering. 8

9 Elements of Sub-metering The terms secondary or sub-metering usually refer to commercial or industrial applications downstream of the main billing meter. Safety Because of the dangerous voltages involved any invasive work should 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 relates to EU harmonised colours and the 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. L1 L2 L3 N 9

10 Types, Characteristics and 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 design meters may have different characteristics to suit the application: Basic A kwh meter with display and kwh pulse used on switchgear outgoing supplies and for connection to a monitoring system. Used widely for compliance to the Building Regulations L2. Multi-function A 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 A specialised meter used to capture transient events and identify problems such as harmonics. Load profile A meter which can 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 A meter with a built-in web server that can be read via your data network or via the internet using a standard browser. 10

11 Accuracy and 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 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 EN 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 the 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 communication 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. 11

12 Electrical Connections The majority of sub-meters sold in the UK are 230V, 3 phase, 4 wire and require current transformers (CTs) above 100A current 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 together, reducing the amount of cabling needed. Not all three phase supplies have a neutral e.g. motor control systems. With these 400V, 3 phase, 3 wire applications only two CTs are required for accurate measurement. High voltage systems are also 3 phase, 3 wire but in addition to using two CTs, voltage transformers are used to reduce the voltage to a safe 110V. Most industrial HV applications are 11000V although 6600V is still common on some sites. 230V 3 Phase 4 Wire Connections Voltage Inputs CT Inputs 230V 400V V1 V2 V3 Vn in 1 out in 2 out in 3 out V Fuses 1 N L1 L2 L3 N 2 3 S1S2 S1S2 S1S2 P1P2 No Load P1P2 P1P2 Current Transformers 12

13 Building Regulations L2 These new regulations came into effect in 2002 and are designed 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 follows: Each separate building or tenanted areas over 500m 2 (Please note if the tenant meter is also to be used to generate the bill, an approved meter must be used). Boilers / CHP plant 50kW and above Chillers 20kW and above Electric humidifiers 10kW and above Motor control centres, pumps and fans above 10kW Electrical distribution boards, circuits above 50kW 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. 13

14 Energy Performance of Buildings Directive (EPBD) The European Union Energy Performance of Buildings Directive was published in the Official Journal on the 4th January 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 was 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 CO 2 emissions, businesses investing in certain energy-saving technologies can benefit from a significant tax break (100% first year capital allowance). These technologies include electricity meters to IEC / EN61036 or BS8431 when used as part of an Automatic Monitoring and Targeting system that meets the required criteria. For further information visit the ECA website at 14

15 Meter Accessories Current Transformers There are a number of reasons for using CTs but the main reason is to do with the physical size of current-carrying cables above A. To accept large diameter cables and to provide adequate insulation the meter would need to be very big and therefore very expensive. Because CTs are able to provide a secondary output with a linear relationship to the primary current, meters can be manufactured in a compact form and at relatively low cost. Generally, 1A or 5A secondary outputs are available with 5A being the most commonly used on new switchgear. If the transformers are likely to be some distance from the meter a 1A CT may be selected in order to keep line losses to a minimum. A CT rated at 600:5 will provide 5A to the meter when the primary current is 600A and 2.5A when the primary current is 300A. For most secondary metering applications it is usually acceptable to use class 1 metering grade CTs. This means at full load, the accuracy will be +/- 1% of the actual current. When combined with a meter offering +/- 1% the overall accuracy of the system, assuming there are no wiring or burden problems, will be +/- 2%. 15

16 Current Transformer Type and Polarity The most common type of metering grade CT is the moulded case type and is suitable for cable or busbar mounting. This is fine for new switchgear installations but not easy to retro-fit to existing switchgear on site. Disconnecting large cables in order to feed them through CTs can be difficult and time consuming, so installers usually prefer to fit split core CTs. All CTs have S1 and S2 secondary terminals that need to be wired to the respective terminals on the meter. The current should flow from S1 to the meter and then back to the CT through S2 in order to maintain the correct polarity and drive the meter registers forward. Current Transformer Accuracy and Burden Manufacturers will not only declare the accuracy of their CTs but also the burden they can handle without compromising that accuracy. Typically a 5A secondary CT will be offered with a 5VA burden rating at Class 1 accuracy. Where any current flows through a device or wire it will meet impedance and resistance. The total burden a CT will need to overcome is calculated by adding together the burden from any device connected such as a meter or summation CT, together with the burden from the secondary wiring. Charts are available to help calculate these wiring losses. 16

17 Burden Charts 1A Cable Size mm mm mm 2 4.0mm Distance (metres) Chart showing relationship between burden and distance for varying cable sizes and a 1A CT Burden (VA) 5A Cable Size mm mm mm 2 4.0mm 2 6.0mm mm Distance (metres) Chart showing relationship between burden and distance for varying cable sizes and a 5A CT 17

18 Summation Current Transformers If a number of outgoing supplies from a switch panel need to be combined to give total consumption for a cost centre, a convenient way to do this is to use summation CTs. Several supplies can be summated but note that the more supplies summated the more difficult it is to resolve any resulting wiring problems. For example if we wish to summate 3 off 3 phase supplies rated at 300:5*, we will need to use 3 summation CTs, one for each phase. These will be rated 5+5+5:5. In other words each summation CT will take in three 5A currents and provide a 5A output to the meter. The meter in turn must be set to the sum of the primary currents = 900A. * The CT primaries must balance in order to give reasonable results and this may mean using a 300A CT on a 100A supply. However, as CTs operate accurately over a wide dynamic range, reasonable accuracy can be achieved. Conversion plates There are still many old electro-mechanical meters in use and the majority do not have a pulsed output. These old meters will need to be replaced if an automatic monitoring system is being installed. Modern digital meters with pulsed outputs are a standard Din 96 size and so will not fit the hole left by the old meter. This problem is easily resolved using a conversion plate usually made of steel and large enough to cover the hole left by the old meter and with a Din 96 hole cut centrally to accept the new meter. 18

19 Fuses and Links It is good practice to fit isolation fuses and CT shorting links so that the meter can be safely isolated in the case of failure or more commonly if an installation wiring fault needs to be corrected. Generally digital meters are designed for 10 years reliable operation but the CTs having no moving or electronic parts, can be used for 30 or more years. Meter Boxes Meter boxes are sometimes used where it is not possible or practical to fit a meter in the existing switchgear. A wall mounting box housing a meter with fuses and shorting links inside is a good solution in these circumstances. Multi-meter Panels If a number of meters are required but cannot be installed on existing switchgear it may be necessary to have a purpose-built panel made. If the purpose of installing the meters is for automatic monitoring then the output from all the meters can be very easily wired within the panel and out to a logger or BMS outstation. 19

20 Meter Installation Safety is always of prime importance so you should only use an installer who is suitably qualified and understands the dangers involved when fitting electricity meters and CTs. Not all electricians are aware of the dangers of leaving CTs open-circuit and the resulting voltages that build up in the wiring. Many meter suppliers will offer to fit and commission the meters and this is the simplest option to take. Using your own electricians will save money and allow the work to be done with minimal disruption to production. The advice here is to make sure the electricians fully understand the job in hand and read the installation manual before starting work. It is sensible to get the supplier to visit site once the work is complete to carry out a commissioning check so that any wiring faults can be corrected. Most unsatisfactory meter projects are due to incorrect installation rather than faulty meters. Common Faults By far the most common fault is incorrect CT polarity where one or more of the CTs have been installed the wrong way round. Assuming the phase loading is balanced, if one of the CTs has reversed polarity it will effectively cancel out one of the two correctly installed CTs and the meter will only be reading a third of the output. If two or more CTs are reversed the meter will not work at all. Clearly if the CTs have been correctly installed but the wiring from one or more of the CTs has been reversed the meter will not operate accurately. 20

21 Another common fault occurs where there is a mismatch between the voltage and current connections to the meter. e.g. if the brown phase voltage is connected to the black phase and the black phase voltage is connected to the grey phase. In order to work accurately meters need to be able to measure not only voltage and current but also the relationship between the waveforms. A shifting of the phase relationship by 120 degrees as described above will confuse the meter and lead to inaccurate readings such as a peculiar power factor. It is very difficult to diagnose this type of fault unless you have an intelligent meter with diagnostics built in. Less Common Faults Correct installation is as important as selecting the right meter for the job, it needs careful consideration. Make sure the CT cabling is adequate and does not overburden the CT. Using 1.5mm 2 cable to carry a 5A secondary current 30 metres to the other side of a switch room will lead to poor accuracy. Check the CT burden charts to make sure the cable is adequate for the job or if you are unsure contact your supplier. Installing CTs on the wrong supply happens more often than you would imagine. The same problem will occur if the cabling to a multi-meter panel gets crossed en route. 21

22 Specifying Sub-meters There is a new British standard for solid state secondary or sub-meters. The argument from a number of manufacturers is that a standard exists for tariff metering (the main billing meter) IEC/BS EN and that a less arduous standard is needed for sub-metering to cover the very wide range of applications secondary metering is used for. However, most good quality sub-meters already meet the international standard IEC/BS EN and at no extra cost. If your main concern is reliable accuracy then simply specify IEC/BS EN From the point of view of the meter specifier it is important to bear a number of points in mind: Accuracy is important and purchasing a class 1 meter which complies with IEC/BS EN will not cost much more than a class 3 device. Use metering grade CTs and specify class 1 accuracy as a minimum. Consider also the whole system and ensure line losses are within the limits of the CT. For tenant billing applications, select meters which are pattern approved for the purpose by Ofgem or have MID approval.. All meters should be installed with fuses and CT shorting links so that for servicing purposes the meter can be fully isolated from the system. Select a meter supplier, a manufacturer or distributor who can provide good technical support. Many metering problems are installation or site related so if things go wrong you may need expert help on site. 22

23 Utility Metering Solutions Ltd. Utility Metering Solutions offers expert guidance on meter selection and a professional installation and commissioning service for meters, data networks and software. Products and Services Electricity Meters Basic kwh with Pulse Multi-function meters with communications Web enabled and power quality meters Ofgem and MID approved billing meters Ancillaries Class 1 metering grade current transformers Fuses and CT shorting link assemblies Single boxes and multi-meter panels Conversion plates for replacing old meters Communication and data logging Multi-channel data loggers Data collecting via Ethernet and internet PSTN and GSM / GPRS modems Software For handheld data collection Automatic collection and analysis Automatic tenant billing Services Consultancy services Site surveys and reports Meter and communications installation Supply/install gas, water, and other utility meters Bureau services 23

24 Application Profiles Company A A large quarry needed to take control of its electricity use with an AMR solution. As the substations were not connected to the phone or data network and as it was not practical to run cables, a GSM solution was devised. Premier meters were installed with GSM modems and linked back to AMR software via the cellular network. Premier meters store half hourly load survey and only need to be contacted once a day for the data to be collected. The result is a very reliable and cost effective solution. Organisation B Government offices wishing to reduce carbon emissions contacted UMS for a turnkey solution. Following a site visit and the provision of a detailed quotation, UMS were commissioned to supply the complete solution. Elite panel meters were installed in the main switchgear and networked to a PC running EASEII Manager software. This solution not only allows load profiling and reporting but also access to real-time power consumption. During the commissioning stage the air curtain system was shown to be running at full load (22kW) 24/7 with no controls. Real-time monitoring can be a very powerful tool in reducing waste and carbon emissions as the impact of switching off unnecessary loads can be seen immediately. Commercial Offices C A major refurbishment had been carried out in an office block but the metering had been overlooked. UMS had been recommended to the managing agents and within a few weeks Ofgem approved billing meters had been installed for billing the commercial tenants. Although automatic meter reading and billing was not required at this stage the meters have the capacity to be networked and read remotely in the future. 24

25 Contractor D Installed Ofgem approved metering on a ROCs scheme. Two identical CHP units are powered from methane gas produced at a sewage works. However, the ROC CHP meters did not agree with the CHP 2 meter showing a consistently lower reading than the CHP 1 meter. Following investigations carried out by the UMS engineer, the problem was traced to a faulty current transformer on one of the phases. Useful Contacts and Links ESTA The Energy Services & Technology Association Ofgem NWML National Weights & Measures Laboratory Building Energy Metering Guide TM39 available from CIBSE Carbon Trust 25

26 26 Notes

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28 If you would like advice or information on the areas covered in this booklet please contact: Utility Metering Solutions Ltd Po Box 9129 Nottingham NG2 9EH The UMS Guide to Metering was written by Alan Ward for UMS Ltd.