Question

In electrodynamometer type wattmeter, the inductance of pressure coil produces error. The error is:

• A. constant irrespective of the power factor of the load
• B. higher at higher power factor loads
• C. higher at lower power factor loads
• D. highest at unity power factor loads

Hint:

Electrodynamometer wattmeters are sensitive to phase shifts caused by coil inductance. The lower the power factor, the greater the error in measurement.

Answer 1

The Correct Option is C

In an electrodynamometer type wattmeter, the pressure coil (also called the voltage coil) has inductance.
This inductance causes the current in the pressure coil to lag behind the voltage, leading to a phase angle error.
At low power factor (typically with inductive loads), this phase error becomes more significant, and the wattmeter reading becomes less accurate.
The error introduced due to the inductance of the pressure coil is directly related to the phase angle between current and voltage, and it increases as the power factor decreases.
Therefore, the error is higher at lower power factor loads.