(i) Driving system
(ii) Moving system
(iii) Braking system
(iv) Registering system (i) Driving System The driving system of an energy meter essentially consists of two electromagnets, called the shunt magnet and series magnet. The core of these electro-magnets is made up of silicon steel laminations; these laminations are riveted together to form a rigid mechanical structure in which definite alignment of parts maintains the correct magnetic flux distribution for consistent performance. The shunt magnet consists f a number of “M” shaped iron laminations assembled together to form a core. A coil having a large number of turns of fine wire is fitted on the middle limb of the shunt magnet. The coil is known as pressure coil and is connected across the supply mains.
The potential coil is highly inductive as it has very large number of turns and the reluctance of its magnetic circuit is very small. The series electro-magnet consists of a number of “Y” shaped iron laminations assembled together to form a core. Each of the limbs is wound with a few turns of heavy gauge wire. This wound coil is known as current coil and is connected in one of the lines and in series with the load to be metered. The series magnet is energized and set up a magnetic field cutting through the rotating disc, when load current flows through the current coil (cc).
Copper shading hands are provided on central limb of shunt magnet so that the phase displacement of 900 between the magnetic field sets up by shunt magnet and applied voltage is achieved by their adjustment. The copper shading bands are also called the power factor compensator or compensating loops. (ii) Moving System The moving system essentially consists of a rotating aluminium disc mounted on a vertical spindle and supported on a sapphire cup contained in a bottom bearing screw. The bottom pivot, which is usually so movable, is of hardened steel and the end, which is hemispherical in shape, rests in the sapphire cup. The top pivot merely reveres to maintain the spindle in a vertical position under working conditions and does not support any weight or exert appreciable thrust in any direction. A pinion engages the shaft with the counting or registering mechanism. The magnetic field produced by shunt electromagnet is pulsating in character and cuts through the rotating disc and induces eddy currents therein, but normally does not, in itself, produce any driving force. The reaction between these two magnetic fields and eddy currents set up a driving torque in the disc. (iii) Braking System The braking system basically consists of a permanent magnet, called the brake magnet. The brake magnet consist of “C” shaped piece of alloy steel bent round to form a complete magnetic circuit, with the exception of a narrow gap between the poles. This magnet is mounted so that the disc revolves in the air gap between the polar extremities. The movement of rotating disc through magnetic field crossing the air gap sets up eddy currents in the disc, which react with the field, and exerts a braking effect. By changing the position of the brake magnet or by diverting some of the flux there from the speed of the rotating disc may be adjusted. (iv) Registering or Counting System The registering or counting system essentially consists of a train of gears, driven by either a worm or pinion gear on the disc shaft, which turns pointers that indicate on dials the number of times the disc has turned. The energy meter thus determines and adds together or integrates all the intravenous power values so that total energy yused over a period of time is known.
There is two types of register mechanism
(i) pointer type
(ii) cyclometer type
In the former type, the pinion on the rotor shaft drives, with the help of a suitable train of reduction gears, a series of five or six pointers rotating on dials marked with ten equal divisions. The gearing between different pointers is such that each pointer advances by tooth of a revolution for a complete revolution of their adjacent pointer on the main rotor disc in the train of gearing as shown.
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