Construction of AC Energy Meter
Energy meters are the basic part to measure the power consumption. It is used everywhere, no matter how big or small consumption it is. It is also known as watt-hour meter. Here we discuss the construction and working principle of induction type energy meter.To understand the structure of watt-hour meter, we must understand the four essential components of the meter. These components are as follows:
- Driving system
- Moving system
- Braking system
- Registering system
Driving SystemThe components of this system are two silicon steel laminated electromagnets. The upper electromagnet is called shunt magnet and it carries a voltage coil consisting of many turns of thin wire. The lower electromagnet is called series magnet and it carries the two current coils consisting of a few turns of thick wire. Current coils are connected in series with the circuit and load current passes through it. Where as voltage coil is connected to the supply mains and produce a high ratio of inductance to resistance. There is copper bands in the lower part of shunt magnet which provides frictional compensation so that the phase angle between shunt magnet flux and the supply voltage is exactly 90o.
Moving SystemAs you can see in the figure, there is a thin aluminum disk placed in the gap between the two electromagnets and mounted on a vertical shaft. The eddy currents are induced in the aluminum disk when it cuts the flux produced by both the magnets. As a result of interference of eddy currents and two magnetic fields constitute a deflecting torque in the disk. As you start consuming power the disk slowly starts rotating and the several rotation of the disk displays the power consumption, in the particular interval of time. Normally it is measured in kilowatt-hours.
Braking SystemThe main part of this system is a permanent magnet called brake magnet. It is located near the disk so that eddy currents are induced in it due to movement of rotating disk through the magnetic field. This eddy current reacts with the flux and exerts a braking torque which opposes the motion of the disk. The speed of the disk can be controlled by changing flux.
Registering SystemAs its name suggest, it registers the number of rotation of the disk which is proportional to the energy consumed directly in kilowatt-hour. There is a disk spindle which is driven by a gear on the disk shaft and indicates the number of times the disk has turned.
Working Principle of Energy MeterThe working of single phase induction type energy meters are based on two main fundamentals:
- Rotation of aluminum disk.
- Arrangement of counting and displaying the amount of energy consumed.