Introduction To Electromechanical Kwh Meter

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    The common type of electric meter is  Electromechanical KWh Meter

    On a single-phase AC power supply, an electromechanical induction meter operates by electromagnetic induction by counting the rotation of a non-magnetic but conductive metal disk. The rotation speed of the disk is proportional to the power passing through the meter. Therefore, the number of revolutions is directly proportional to energy usage. The voltage coil consumes a small amount of relatively constant power, usually about 2 watts, which is not recorded on the meter. Similarly, the current coil consumes a small amount of power in proportion to the square of the current flowing through it, usually up to a few watts under full load, and this power is recorded on the meter.

    The disc is acted by two groups of induction coils, which actually forms a two-phase linear induction motor. One coil is connected in such a way that it generates a magnetic flux proportional to the voltage, while the other coil generates a magnetic flux proportional to the current. Due to the inductance of the coil, the magnetic field of the voltage coil will be delayed by 90 degrees, and a hysteresis coil is used for calibration. This creates eddy currents in the disk, whose role is to make the force proportional to the product of the instantaneous current, voltage, and phase angle (power factor) between the disk. The permanent magnet acts as an eddy current brake, exerting a reaction force proportional to the rotation speed of the disk. The balance between these two opposing forces causes the disk to rotate at a speed proportional to the power or energy usage rate. The optical disc drives an alignment mechanism that counts the number of revolutions, much like an odometer in a car, in order to measure the total energy used.

    Different phase configurations use additional voltage and current coils.


    Three-camera electric induction meter, measuring 100 A 240/415 V power supply. A horizontal aluminum rotor disc can be seen in the center of the instrument. The disc is supported by a spindle with a worm gear that drives the register. The register is a series of dials that record the power consumed. The dial can be an odometer type, similar to the display of an odometer, easy to read, where each dial displays a number through a window on the surface of the meter, or a pointer type, where the pointer indicates each number. For the dial pointer type, adjacent pointers usually rotate in opposite directions due to the gear mechanism.

    The amount of energy represented by one rotation of the disc is represented by the symbol Kh, which is given in units of watt-hour/revolution. The value 7.2 is common. Using the Kh value, it is possible to determine their power consumption at any given time by timing the discs with a stopwatch.

    {\ displaystyle P = {{3600 \ cdot Kh} \ over t}} P = {{3600 \ cdot Kh} \ over t}.

     

    t = the time it takes for the disc to complete one lap, in seconds,
    P = power (watts).
    For example, if Kh = 7.2, and it makes one revolution in 14.4 seconds, the power is 1800 watts. This method can be used to determine the power consumption of the household devices by turning on the household devices one by one.

    Most household electricity meters must be manually read by a representative of the power company or customer. Where the customer reads the meter, the reading can be provided to the power company by phone, mail, or via the Internet. The power company will usually require company representatives to visit at least once a year to verify the readings provided by the customer and perform basic safety checks on the meter.

    In an induction meter, creep is a phenomenon that may adversely affect accuracy. Creep occurs when the meter dial is continuously rotated under the condition of an applied electric potential and the load terminal is open. The erroneous test caused by creep is called creep test.

    There are two standards for instrument accuracy, ANSI C12.20 and IEC 62053 in North America.


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