We all know that the electric meter is in kilowatt-hours, which means the energy consumed by an electrical appliance with a power of one kilowatt after one hour of use, so there is also a kilo watt-hour meter .
In the "voltage coil", the current lags behind, and the magnetic field lines also lag. Therefore, the magnetic field generated by the electromagnet above lags; in the "current coil", the load current does not lag, and the magnetic field lines generated by it do not lag. Therefore, the magnetic field generated by the electromagnet below does not lag. In this way, the lower magnetic field is always generated before the upper magnetic field.
Now, assuming that the power supply voltage reaches the maximum value, the load current also reaches the maximum value, and magnetic lines of force are generated from the current coil. When the power supply voltage tends to zero, as the load current becomes smaller, the magnetic field lines of the current coil also decrease. When the current in the voltage coil becomes larger, the lines of magnetic force are generated from it. Since the power supply voltage has positive and negative polarity changes (AC), the magnetic lines of force come out of the current coil again. In this way, it is equivalent to a magnet doing a rotating motion. As a result, the aluminum plate will rotate.
The three phase electricity meter is also calculated in kilowatt-hours.