Exam Question

(a) Effect of power factor on:
(i) Induction motors:  Induction motors typically have a lagging power factor, meaning the current lags behind the voltage. This is because of the inductive nature of their windings. The power factor is generally between 0.7 and 0.9, and it varies depending on the motor's load and design. A fully loaded motor will usually have a higher power factor than a lightly loaded one.
(ii) Transformers:  Ideally, transformers should have a unity power factor (1.0), meaning the current and voltage are in phase. However, in reality, they exhibit a slightly lagging power factor due to the core losses (hysteresis and eddy currents) and magnetizing current. These losses are relatively small, resulting in a power factor close to unity.
(iii) Partly loaded motors:  Partly loaded induction motors operate at a lower power factor than fully loaded ones. This is because the magnetizing current (which is reactive and doesn't contribute to real power) forms a larger proportion of the total current when the motor is lightly loaded. The power factor decreases as the load decreases.