Polyphase Energy Meter

In polyphase circuit, the energy can be measured by a group of single-phase energy meters as required by Blondel’s theorem. As per Blondel’s theorem, the total energy consumed is the sum of readings of all energy meters. However, in actual practice this is never done. In commercial, measurement, polyphase meters used which are constructed by combining two or more single phase energy meters in one unit.  Polyphase meters may be ‘multi-disc type’. In the multi-disc type, each element drives a separate disc. In the single disc type meter, all the elements drive the same disc. This disc is slotted or laminated in sector to prevent interaction between eddy currents produced by one element with the flux produced by another element.

Two element energy meters:

A two-element energy meter used for measurement of energy in 3-phase, 3- wire circuit.

It consists of two discs mounted on common spindle. The moving system drives a single gear train. Each unit is provided with its own shading ring, shading bands and break magnet for adjustments.

 It is essential that the driving torque of two elements be exactly the same for the same power passing through them. This condition is checked by energizing the coils from a single circuit, the two pressure coils being connected in parallel and the circuit coils in series, with one reversed to oppose the other. This arrangement causes the two torques to be in opposition and if the two torques are equal, the disc will not rotate. If there in slights motion, the magnetic shunt is adjusted till the speed of the discs become zero. The lag, light load and unity power factor adjustments are made independently for each element.

Also Read- Dynamometer type single-phase power factor meter

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