Introduction
This is a device which is employed to quantity of the electrical energy which is consumed in business, at the residence and in electrically powered devices like refrigerators. Many at times electric utility applies energy meters at the customers’ premises to help take the measurements of electric energy delivered to the ir customers for billing reasons (Sahay, 2012). These devices are calibrated in billing units; the most popular one is kilowatt hour.
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Working principle of single phase energy meter
This meter operates on the principle of Ferraris type motor; the input voltage is supplied to the potential coil. The current flowing across the potential coil is always proportionate to supply voltage, but it lags it by 900, because its winding resistance is very small. The potential coil current Ip produces a flux which divides into a significant portion of the side gap and also across the disc, whose value is relatively small. Hence the flux is accountable for generating the driving torque. It is proportionate to the Ip and also in phase with it. The flux/prompts/ induces an eddy EMF in the disc situating an eddy current Ip. (Tumiran, 2013) The load current I move through the current coil, and it produces a flux which is directly proportionate current I and also in phase with it.
This flux induces an eddy EMF in the disc putting up the eddy current IS . The phasor diagram of this energy meter is illustrated in the diagram below. Torque will be produced by the interaction of the current Is and. Another torque is also generated from the interaction of eddy current Ip and . These two produced torques are in the opposite direction, and thus the net torque will be found by getting the difference between them, this will make the disc to rotate. If voltage V is supplied at a frequency f Hz, I be the load current and Z be the impedance of the eddy current path and be the pressure coil and the current coil flux respectively. Hence the mean torque deflecting the disc is obtained by the following equations;
The diagram below shows a phasor diagram for an energy meter,
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From the equations,
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If N is given as the steady speed rotation of the moving disc, so the controlling torque which is proportionate to this speed is provided by the following equation (U.A.Bakshi, 2013).
If the potential coil flux and the voltage phasor are kept constant in quadrature, so and we then obtain,
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From the above analysis, we can conclude by saying that the total number of revolution of the disc is the right to value of the energy consumed by load circuit.
Causes of error in energy meter
The energy meter is subjected to some errors; these errors may arise from the following; errors in the driving system. These errors arise because of the wrong magnitude of flux value, phase angle and also the absence of symmetry in the magnetic field. Another source is errors from braking systems. These errors like the changes in the strength of the brake magnet, variation in disc resistance, the self-braking effect of series magnet flux and also anomalous friction of the parts moving (nniolop, 2011). The third source of error is the errors due to registering systems. These are also expected to be found in this meter. These errors are always taken care of by calibration of the meter (Jumwa, 2011). The fourth source of error due to the speed. In some cases the speed of the meter is either higher the normal speed or lower than the normal speed, this may lead to a wrong value of the energy consumption recorded. The errors due to the speed can be eliminated by correctly adjusting the speed of the brake magnet to help control the speed of the meter.
Calibration of energy meter
When the calibration of the energy meter is done then accuracy should be highly considered. The way to ensure this accuracy of the energy meter is to do the calibration independently. In the process of doing so, it is critical that the calibration should be done based on the international standards. That will make the energy meter to be accepted worldwide. The devices employed to calibrate the energy meters should be routinely verified, that will profoundly protect the customers of electric power (Batra, 2014). These calibrations are only done in the Laborelec Lab. This is the only lab in the world where the calibration is done; the lab is located in Belgium. This Lab always aligns the portable standards used in doing the calibration.
Bibliography
Batra, P., 2014. Measurement of Energy Using Digital Meter and Tamper Proof Electronic Energy Meter: Summer Internship in Electronics/Electrical Field. 3rd ed. London: BlinkWink.
Jumwa, D., 2011. UPM EM 100 Energy Meter. 1st ed. Chicago: Sustainability Program.
nniolop, B., 2011. Electrical Measurements and Measuring Instruments. 2nd ed. New York: Technical Publications.
Sahay, K., 2012. Basic Concepts of Electrical Engineering. 2nd ed. Hull: New Age International.
Tumiran, M. R., 2013. Energy meter. 2nd ed. Manchester : Universiti Teknologi.
U.A.Bakshi, A., 2013. Electrical Measurements And Measuring Instruments. 1st ed. London: Technical Publications.
