Energy Meter

Energy meter:

Energy meteris a device that measures the amount ofelectric energyconsumed by aresidence, abusiness, or an electrically powered device. Electric utilitiesuse electric meters installed at customers' premises to measure electric energy delivered to their customers for billing purposes. They are typically calibrated in billing units, the most common one being thekilowatt hour [kWh]. They are usually read once each billing period. Energy meters operate by continuously measuring the instantaneousvoltage(volts) andcurrent(amperes) to giveenergy used (injoules, kilowatt-hours etc.). Meters for smaller services (such as small residential customers) can be connected directly in-line between source and customer. For larger loads, more than about 200 ampere of load,current transformersare used, so that the meter can be located other than in line with the service conductors. The energy meters divided into two basic categories, electromechanical and electronic.

Electromechanical Type Energy meter:

Induction type energy meters are most commonly form of an electromechanical A. c. KWh meter used to measure the energy consumed in any a.c. circuit in a prescribed period when supply voltage and frequency are constant, in day today life & in industrial installation. Energy meter is an integrating instrument which measure the total quantity of electrical energy supplied to the circuit in a given period. These meters measure electrical energy in Kilowatt hours.

PRINCIPLE:

The Basic principle of induction type energy meter is electromagnetic induction. When an alternating current flows through two suitably located coils (Current coil & Potential Coil) produces rotating magnetic field which is cut by the metallic disc Suspended near to the coils, thus, an e.m.f. is induced in the thin Aluminum disc which circulates eddy currents in it. By the interaction of Rotating magnetic field & eddy currents, torque is developed & causes the disc to rotate. This is the same principle which is applied in the single-phase induction motors.

Construction:

An Induction type single phase energy meter, has following main parts of the operating mechanism:

1. Driving System
2. Moving System
3. Braking System
4. Registering System

1.Driving System

It develops torque to rotate the moving system. It consists of two electromagnets one is formed by current coil & other one is by voltage coil or pressure coil.

2.Moving Coil

It essentially consists of an aluminum mounted on the spindle which is supported by Pivot-jewel Bearing system. Since there is not control spring, the disc makes continuous revolution under the action the deflecting torque.

3.Braking Coil

It consists of a permanent magnet of C shaped covering a part of rotating disc to provide braking torque. By changing the position of breaking magnet, the Flux linkage with the disc can be changed, this torque is opposite to driving torque.

4.Registering System

It keeps the record of energy consumed by load through worm wheel or pinion gear mounted with spindle of moving disc.

Working:

When the energy meter is connected in the circuit, the current coil carries the load current and the pressure coil carries the current proportional to the supply voltage. The magnetic field produced by the SERIES magnet (series coil) is in phase with the line current & the magnetic field produced by the shunt magnet (pressure coil) is in quadrature with the applied voltage (since the coil is highly inductive). Thus, a phase difference exists between the fluxes produced by the two coils. This sets up a rotating field which interacts with the disc and produces a driving torque and, thus, disc starts rotating. The number of revolutions made by the disc depends upon the energy passing through the meter. The spindle is geared to the recording mechanism so that electrical energy consumed in the circuit is directly registered in KWh. The speed of the disc is adjusted by adjusting the position of the breaking magnet. For example, if the energy meter registers less energy than the energy actually consumed in the circuit, then the speed of disc has to be increased which is obtained by shifting the magnet nearer to the centre of the Disc and vice-versa.

At constant angular speed the power is proportional to the angular speed in r.p.s. We calibrate w and energy meter by time test.

Let K be the meter constant of energy meter, which is the number of revolution per KWh energy consumption. When connected to measure energy, if disc makes R number of revolution in t seconds. Then the reading of energy meter is:

Let,

KW= Power in Kilowatt from wattmeter reading.

R= No. of revolution made by disc in ‘t’ Sec.

Let the wattmeter reading be Kw watts of energy calculated from the wattmeter & stop watch is given by

Electronic meter

Electronic meters display the energy used on anLCDor LED display, and some can also transmit readings to remote places. In addition to measuring energy used, electronic meters can also record other parameters of the load and supply such as instantaneous and maximum rate of usage demands,voltages,power factorandreactive powerused etc. They can also support time-of-day billing, for example, recording the amount of energy used during on-peak and off-peak hours.

References:

1.https://en.wikipedia.org/wiki/Electricity_meter

2."Handbook for Electricity Metering" by The Edison Electric Institute—The Bible of electricity meters