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5. What are the errors in induction watt-hour meter? , What is Error in Induction Watthour Meter?

# What are the errors in induction watt-hour meter? , What is Error in Induction Watthour Meter?

Hello friends, in this article we will know that what are the errors in Induction Watthour Meter? How are errors in Induction Watthour Meter corrected? And learn about many facts related to it.

## Errors in Induction Watt-Hour Meter | Error in Induction Watthour Meter

electrical energy The users are charged according to the readings of the energy meters installed in their premises. Therefore, it is very important that energy meters are built and designed to ensure accuracy over a long period of time, i.e. they give accurate readings over a period of several years under normal use conditions.

Something Common in Energy Meters errors (Error in Induction Watthour Meter, And their remedial measures are discussed below:

## Phaser Error | Phasor error in Induction watthour meter

The meter will read correctly only when the shunt magnet flux lags exactly 90° behind the supply voltage. Since the shunt magnet coil has some resistance and is not completely reactive, the shunt magnet flux does not reduce the supply voltage by exactly 90 degrees. As a result, the meter does not read correctly at all power factors.

Adjustment. The flux in the shunt magnet can be made to lag exactly 90° to the supply voltage by adjusting the position of the shading coil placed around the lower part of the central limb of the shunt magnet. The current is induced in the shedding coil by the shunt magnet flux and causes further displacement of the flux.

By moving the shading coil up or down, the displacement between the shunt magnet flux and the supply voltage can be adjusted up to 90 degrees. This adjustment is known as interval adjustment or power factor adjustment.

## speed error | Speed ​​Error in Induction Watthour Meter

Sometimes the disc speed of the meter is either faster or slower, resulting in incorrect recording of energy consumption. Adjustment. The disc speed of the energy meter can be adjusted to the desired value by changing the position of the brake magnet. If the brake magnet is moved toward the center of the axle, the braking torque decreases and the disc speed increases. If the brake magnet is moved away from the center of the axle the reverse will happen.

## friction error | Frictional Error in Induction Watthour Meter

Frictional forces in rotor bearings and counting mechanisms cause a noticeable error, especially at light loads. At light loads, the torque produced by friction greatly increases the braking torque. Since the force of friction is not proportional to the moment of speed but is roughly constant, this can lead to considerable error in meter readings.

Adjustment, to compensate for this error, is necessary to provide a constant addition to the driving torque that is equal and opposite to the friction torque. This shunt is produced by means of two adjustable short-circuited loops placed in the leakage gap of the magnet. These loops disturb the symmetry of the leakage current and generate a small torque to oppose the frictional torque.

This adjustment is known as the light-weight adjustment. The loops are adjusted so that when no current passes through the current coil (i.e. the exciting coil of the series magnet), the torque produced is sufficient to overcome friction in the system, without actually rotating the disc.

## creep | creeping

Sometimes the disc of the meter rotates slowly but continuously at no-load, i.e. when the potential coil is excited but no current flows through the load. This is called creep. This error can be caused by over-compensation for friction, excessive supply voltage age, vibration, stray magnetic field adjustment, etc. To prevent this creep, two diametrically opposite holes are drilled in the disc. This causes substantial distortion of the field. The result is that the disc remains stationary when a hole is hit under one of the poles of the shunt magnet.

## temperature error | Temperature error

Since watt hour meters are often required to operate in outdoor installations and are subject to extreme temperatures, the effects of temperature and their compensation are very important. The resistance of the disc, the potential characteristics of the coil and magnetic circuit, and the strength of the brake magnet are affected by changes in temperature, so great care is taken in the design of the meter to eliminate errors due to te temperature variation.

## Frequency Variations | Frequency variations

The meter is designed to give minimum error at a particular frequency (usually 50 Hz). If the supply frequency changes, the reactance of the coil also changes, resulting in a small error. Fortunately, this is not of much importance as commercial frequencies are kept within a limited range.

## Voltage Variations | Voltage variations

voltage With an increase in shunt magnet flux will increase. The driving torque is proportional to the first power of the flux while the braking torque is proportional to the square of the flux. Therefore, if the supply voltage is higher than the normal value, the braking torque will increase much more than the driving torque and vice versa. As a result, the meter has a tendency to operate at a slower than normal voltage and faster at a lower voltage.

However, for most meters the effect is small and does not exceed 0.2% to 0.3% for a voltage change of 10% from the rated value. Small error due to voltage variation can be eliminated by proper design of magnetic circuit of shunt magnet.