ERRORS OF SINGLE PHASE ENERGY METER AND ADJUSTMENTS

Following are the errors which may creep in an energy and to the make correction , some adjustments suggested along with the errors.

1. Phase and Speed Errors:
The phase errors is introduced because the shunt magnet flux does not leg behind the supply voltage by exactly 90 degree due to some resistance of the coil and iron losses. the angle less slightly less then 90 degree.Because this errors the torque is not zero at zero power factor of the load.

In order to remove this error, made supply voltage exact 90 degree . this is accomplished by adjusting the position of copper shading band provided on central limb of the shunt magnet. an error on the fast under these condition can be eliminated by bringing the shading and near to the disc and vice-versa

Sometimes, the speed of the disc of energy meter is faster or slower , when tested on a load having power factor. there, energy meter register either more or less energy and errors is introduced.

In order to remove this error, the redial position of the braking magnet is adjusted. movement of braking magnet , away from the centre of the disc increase the torque which decreases the speed of the Disc.

2. Frictional Error:  
This error is introduce due to friction at the rotor bearing and the register mechanism. because this error is unwanted braking torque acts on the moving system and register less energy then the actual energy passing though it

This error is compensated by placing two short circuited bands on the outer limbs of the shunt magnet. these bands embrace the flux contain in two outer limbs of of the shunt magnet. An emf induce circulating current though them. this causes phase displacement between the enclose flux and main flux. As a result of this , a small driving torque is exerted on the disc solely by pressure coil which compensate the friction torque.

3. Creeping error:
The slow but continuous rotation of energy meter , which only pressure coil is excited but no current flow though the current coil is called creeping.this error may be due to excessive friction compensation, excessive voltage supply and stray magnetic field etc.

In order to prevent creeping on no load , two holes are drilled in the disc on the opposite side of the spindle at the same radius , this causes sufficient distortion of the field to prevent continuous rotation.

4. Temperature Error: 
By changing the temperature , the parameter of the coils change slightly which introduce a small error in meter. however , this error negligible small and there is no need to prevent any means to eliminate the error.

5. Frequency Error:
Since the energy meter are used normally at fixed frequency, therefore , they are designed and adjusted to have minimum error declared supply frequency Which is normally 50 Hz in India.