An electric meter or energy meter is a device that measures the amount of electrical energy supplied to customers of an electric supply company.Electricity providers must install and maintain meters at all customer locations, at the provider’s expense, to ensure proper measurement and billing of electric service. Utilities record the values measured by these meters to generate an invoice for the electricity. At present, energy meters based on electromagnetic technology and static meters are being used in the Indian distribution network. Single phase meters are being used for most of the domestic and some commercial consumers, whereas 3-phase meters aremnbeing used for industrial, agricultural and large commercial consumers.
Energy meters typically consist of an energy measurement apparatus for measuring energy consumption and a gauge that is visible outside the meter for showing the amount of electrical quantities including the energy consumed. Electricity meters track among other things, the amount of energy consumed,typically measured in kilowatt-hours (kWh), at each customer's facility. The available technology options are given in Box .
Box : Available Technology Options for Metering
i) Electromechanical meters (Ferraris wheel meters);
ii) Hybrid meters;
iii) Static (electronic) meters;
iv) Demand meters;
v)Multiple tariff (variable rate) meters/Time of Usage (TOU) meters;
vi) Prepaid meters;
vii) Automatic Meter Reading (AMR) and Remote Meter Reading (RMR).
We now describe these meters and their working, in brief. You may skip the technical details if you find them difficult to understand. But do focus on their relative merits.
i)Electromechanical Meters
Electromechanical energy meters (Fig. ) are based on the Ferraris Principle (see note in the margin). The working of these meters is explained in Box .
Box : Working of Electromechanical Meters
The meters have a revolving metallic disc mounted on jewel bearings/magnetic suspension bearings. The display is cyclometer or mechanical counters and accuracy is typically 1% or 2% (class 1.0 or 2.0). They cater to limited tariffs applicable mainly to 1-phase or 3-phase direct connected segment (whole current meters).The electromechanical induction meter operates by counting the revolutions of the disc, which rotates at a speed proportional to the power consumed. The number of revolutions is, thus, proportional to the energy usage. The metallic disc is acted upon by three magnetic fields, one proportional to the voltage, another to the current and a third constant field supplied by a permanent magnet. One of the varying fields induces currents in the metallic disc, which are then acted upon by the other varying field to produce a torque.This results in the torque being proportional to the product of the current and voltage, i.e., power. As the metallic disc rotates through the permanent magnetic field, eddy currents are again produced which dissipate energy (since the disc has some resistance) and act to slow the rotation. This drag is proportional to the rotation speed. The equilibrium between the applied torque and the drag results in a speed proportional to the power. The rotating disc in this type of meter is, in fact, an electric motor of a type called a reluctance motor or eddy current motor. It consumes a small amount of power, typically around 2 W.
ii) Hybrid Meters
These meters have electronic measurement circuits but display is through impulse counters/stepper motors. Accuracy is typically class 1.0 or 2.0 and generally these meters cater to limited tariffs applicable mainly to single phase or 3-phase direct connected segment.
iii) Static (Electronic) Energy Meters
Electronic energy meters (Fig.) are replacing traditional electromechanical meters in many residential, commercial and industrial applications because of the versatility and low-cost afforded by electronic meter designs. The measurement circuits are electronic with LED (Light Emitting Diode)/LCD (Liquid Crystal Display) display and their accuracy is typically class 0.2, 0.5, 1.0. They cater to multiple tariffs for all segments CT-VT (Current Transformer – Voltage Transformer) operated, CT operated, 1-phase or 3-phase Direct connected segment. These meters measure and record active, reactive and apparent demand/energy. The static energy meters are microprocessor based and have non-volatile memory to record and store data. The electronic meter in its basic form has a power supply, a metering engine, a processing and communication engine, i.e., a microcontroller, other add-on modules such as Real Time Clock (RTC), LCD display, communication ports/modules, etc.
These meters are extremely difficult to tamper with and if somebody does attempt to tamper them, they will send alarm signals and record the information. The programmability of microprocessor has become a useful tool for incorporating different features like Tamper data, Import-Export, Time-of day metering, load pattern analysis, etc. They can be made SCADA (Supervisory Control and Data Acquisition) systems compatible. They can have communication ports to support AMR/RMR on various communication platforms as well as for downloading of data.
Energy meters typically consist of an energy measurement apparatus for measuring energy consumption and a gauge that is visible outside the meter for showing the amount of electrical quantities including the energy consumed. Electricity meters track among other things, the amount of energy consumed,typically measured in kilowatt-hours (kWh), at each customer's facility. The available technology options are given in Box .
Box : Available Technology Options for Metering
i) Electromechanical meters (Ferraris wheel meters);
ii) Hybrid meters;
iii) Static (electronic) meters;
iv) Demand meters;
v)Multiple tariff (variable rate) meters/Time of Usage (TOU) meters;
vi) Prepaid meters;
vii) Automatic Meter Reading (AMR) and Remote Meter Reading (RMR).
We now describe these meters and their working, in brief. You may skip the technical details if you find them difficult to understand. But do focus on their relative merits.
i)Electromechanical Meters
Electromechanical energy meters (Fig. ) are based on the Ferraris Principle (see note in the margin). The working of these meters is explained in Box .
Box : Working of Electromechanical Meters
The meters have a revolving metallic disc mounted on jewel bearings/magnetic suspension bearings. The display is cyclometer or mechanical counters and accuracy is typically 1% or 2% (class 1.0 or 2.0). They cater to limited tariffs applicable mainly to 1-phase or 3-phase direct connected segment (whole current meters).The electromechanical induction meter operates by counting the revolutions of the disc, which rotates at a speed proportional to the power consumed. The number of revolutions is, thus, proportional to the energy usage. The metallic disc is acted upon by three magnetic fields, one proportional to the voltage, another to the current and a third constant field supplied by a permanent magnet. One of the varying fields induces currents in the metallic disc, which are then acted upon by the other varying field to produce a torque.This results in the torque being proportional to the product of the current and voltage, i.e., power. As the metallic disc rotates through the permanent magnetic field, eddy currents are again produced which dissipate energy (since the disc has some resistance) and act to slow the rotation. This drag is proportional to the rotation speed. The equilibrium between the applied torque and the drag results in a speed proportional to the power. The rotating disc in this type of meter is, in fact, an electric motor of a type called a reluctance motor or eddy current motor. It consumes a small amount of power, typically around 2 W.
ii) Hybrid Meters
These meters have electronic measurement circuits but display is through impulse counters/stepper motors. Accuracy is typically class 1.0 or 2.0 and generally these meters cater to limited tariffs applicable mainly to single phase or 3-phase direct connected segment.
iii) Static (Electronic) Energy Meters
Electronic energy meters (Fig.) are replacing traditional electromechanical meters in many residential, commercial and industrial applications because of the versatility and low-cost afforded by electronic meter designs. The measurement circuits are electronic with LED (Light Emitting Diode)/LCD (Liquid Crystal Display) display and their accuracy is typically class 0.2, 0.5, 1.0. They cater to multiple tariffs for all segments CT-VT (Current Transformer – Voltage Transformer) operated, CT operated, 1-phase or 3-phase Direct connected segment. These meters measure and record active, reactive and apparent demand/energy. The static energy meters are microprocessor based and have non-volatile memory to record and store data. The electronic meter in its basic form has a power supply, a metering engine, a processing and communication engine, i.e., a microcontroller, other add-on modules such as Real Time Clock (RTC), LCD display, communication ports/modules, etc.
These meters are extremely difficult to tamper with and if somebody does attempt to tamper them, they will send alarm signals and record the information. The programmability of microprocessor has become a useful tool for incorporating different features like Tamper data, Import-Export, Time-of day metering, load pattern analysis, etc. They can be made SCADA (Supervisory Control and Data Acquisition) systems compatible. They can have communication ports to support AMR/RMR on various communication platforms as well as for downloading of data.
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| a) Electromechanical Energy Meter; and b) Electronic Meter |
iv) Demand Meters
Demand meters measure volt-amperes (in kVA), which combine both reactive (reflected) and actual (consumed) power. In its simplest form, a demand meter has a gauge whose pointer moves a marker. When the gauge falls back, friction keeps the marker in place. When a demand meter is read, its marker is reset, usually with a magnet from outside the sealed meter enclosure. Computerized demand meters usually find the fifteen-minute interval in the month with maximum demand (MD). Often they also record a month worth of fifteen-minute averages. Some demand meters measure the temperature of a conductor, or simulate the heating ofthe conductor, in order to track "running" demand. Running demand meters usually log the times when a maximum demand is exceeded, or they log the times when the meter enters a different tariff rate.
Electricity cannot be stored, so electricity retailers need to arrange the necessary generators to meet the maximum demand. New generators are long-term capital investments, so demand also directly affects the retailers' and power-providers' accounting, and need for long-term debt. In particular, when interest rates are high, generating companies are reluctant to install new capacity, and want customers to reduce demand,so the retailers use meters to detect and surcharge high demand.
v) Multiple Tariff (Variable Rate) Meters/TOU Meters
Time of use metering facilitates load control and planning on the part of utilities. This is effectively achieved using a concept called Time of Usage (TOU) metering. This involves dividing the day, month and year into tariff slots and with higher rates at peak load periods and low tariff rates at off-peak load periods. Electric utilities may charge customers different tariffs at different times of the day with the help of this type of metering.This is because there is generally a surplus of electrical generation capacity at times of low demand, such as during the night. Such multiple tariffs can be made applicable only by time of use (TOU) meters, which incorporate or are connected to a time switch and which have multiple registers.
Domestic variable-rate meters normally permit only one (uniform) or two tariffs (“peak” and “off-peak”) and in such installations a simple electromechanical time switch may be used. Large commercial and industrial premises may use electronic meters which record power usage in blocks of half an hour or less. This is because most electricity grids have demand surges throughout the day and the power company may wish to give incentives to large customers to reduce demand at these times. Some multiple tariff meters use different tariffs for different amounts of demand. These are usually industrial meters.
The multiple tariff rates may also be dependent of frequency, also known as availability based tariff (ABT), deployed in grid substations and inter-utility transfer points for bulk transfer of energy. This is based on the premise that the system frequency is inversely proportional to the current load. This also causes self-regulation because the rates are higher when the system frequency is low, eventually bringing down the demand. ABT compliant meters also known as Special Energy Meters (SEMs) record and store data on electrical quantities in blocks of 15 minute period, which are downloaded for billing purposes at the time of meter reading.
vi) Prepaid Meters
Prepaid metering is a system whereby consumers purchase electricity through a smart card. The amount paid together with other information is encoded in the smart card. In order to transfer the credit, the consumer inserts the card in the meter. The meter reads the data and when the paid for energy has been used up, the consumer gets the card reloaded/ reprogrammed. The system has the capability of programming with multiple rates, time of use tariffs, etc.
Demand meters measure volt-amperes (in kVA), which combine both reactive (reflected) and actual (consumed) power. In its simplest form, a demand meter has a gauge whose pointer moves a marker. When the gauge falls back, friction keeps the marker in place. When a demand meter is read, its marker is reset, usually with a magnet from outside the sealed meter enclosure. Computerized demand meters usually find the fifteen-minute interval in the month with maximum demand (MD). Often they also record a month worth of fifteen-minute averages. Some demand meters measure the temperature of a conductor, or simulate the heating ofthe conductor, in order to track "running" demand. Running demand meters usually log the times when a maximum demand is exceeded, or they log the times when the meter enters a different tariff rate.
Electricity cannot be stored, so electricity retailers need to arrange the necessary generators to meet the maximum demand. New generators are long-term capital investments, so demand also directly affects the retailers' and power-providers' accounting, and need for long-term debt. In particular, when interest rates are high, generating companies are reluctant to install new capacity, and want customers to reduce demand,so the retailers use meters to detect and surcharge high demand.
v) Multiple Tariff (Variable Rate) Meters/TOU Meters
Time of use metering facilitates load control and planning on the part of utilities. This is effectively achieved using a concept called Time of Usage (TOU) metering. This involves dividing the day, month and year into tariff slots and with higher rates at peak load periods and low tariff rates at off-peak load periods. Electric utilities may charge customers different tariffs at different times of the day with the help of this type of metering.This is because there is generally a surplus of electrical generation capacity at times of low demand, such as during the night. Such multiple tariffs can be made applicable only by time of use (TOU) meters, which incorporate or are connected to a time switch and which have multiple registers.
Domestic variable-rate meters normally permit only one (uniform) or two tariffs (“peak” and “off-peak”) and in such installations a simple electromechanical time switch may be used. Large commercial and industrial premises may use electronic meters which record power usage in blocks of half an hour or less. This is because most electricity grids have demand surges throughout the day and the power company may wish to give incentives to large customers to reduce demand at these times. Some multiple tariff meters use different tariffs for different amounts of demand. These are usually industrial meters.
The multiple tariff rates may also be dependent of frequency, also known as availability based tariff (ABT), deployed in grid substations and inter-utility transfer points for bulk transfer of energy. This is based on the premise that the system frequency is inversely proportional to the current load. This also causes self-regulation because the rates are higher when the system frequency is low, eventually bringing down the demand. ABT compliant meters also known as Special Energy Meters (SEMs) record and store data on electrical quantities in blocks of 15 minute period, which are downloaded for billing purposes at the time of meter reading.
vi) Prepaid Meters
Prepaid metering is a system whereby consumers purchase electricity through a smart card. The amount paid together with other information is encoded in the smart card. In order to transfer the credit, the consumer inserts the card in the meter. The meter reads the data and when the paid for energy has been used up, the consumer gets the card reloaded/ reprogrammed. The system has the capability of programming with multiple rates, time of use tariffs, etc.
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| Prepaid Meter |
The use of prepaid meters results in almost total elimination of non- payment and delayed payment and enables transfer of reliable,accurate and up to date consumption and billing data according to tariff policy in use. This information can be utilized by the utility for demand forecasting and for controlling peak demands. It also means substantial reduction in staff for meter reading, bill serving, bill complaints and bad debts, etc. Full meter programmability allows maximum flexibility in changing tariffs.Consumer can also decide in advance the affordable level of expenditure, which helps him and the utility in elimination of disputes regarding inaccurate bills.
vii) Automatic Meter Reading (AMR) and Remote Meter Reading (RMR)
Automatic Meter Reading (AMR) and Remote Meter Reading (RMR)
describe various systems that allow meters to be checked without the need to send a meter reader out. This can be effectively achieved using off-site metering, that is an electronic meter is placed at the junction point where all the connections originate, inaccessible to the end-user and it relays the readings via the AMR technology to the utility. Remote metering enables online metering of energy consumption. It is particularly useful for high value consumers where accuracy of billing and delays in time taken for meter reading are important. Monitoring of consumption patterns to detect theft/ tampering of meters is possible with these types of meters.
The remote metering unit may be the RTU (Receiving Transmitting Unit),which receives the pulses generated by the electronic meters and is communication system which could be PLC (Programmable Logic Control), public switched telephone network, radio, etc.SAQ 1: Metering technologies
describe various systems that allow meters to be checked without the need to send a meter reader out. This can be effectively achieved using off-site metering, that is an electronic meter is placed at the junction point where all the connections originate, inaccessible to the end-user and it relays the readings via the AMR technology to the utility. Remote metering enables online metering of energy consumption. It is particularly useful for high value consumers where accuracy of billing and delays in time taken for meter reading are important. Monitoring of consumption patterns to detect theft/ tampering of meters is possible with these types of meters.
The remote metering unit may be the RTU (Receiving Transmitting Unit),which receives the pulses generated by the electronic meters and is communication system which could be PLC (Programmable Logic Control), public switched telephone network, radio, etc.SAQ 1: Metering technologies
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