The primary reason for low power factor in the supply system is due to installation of

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induction motor

Explanation: The primary reason for a low power factor in industrial supply systems is the widespread use of induction motors, which are highly inductive loads. These motors draw a significant amount of lagging reactive power ($Q = VI \sin \phi$) from the supply to establish their rotating magnetic fields.

Working Principle: Induction motors operate on the principle of electromagnetic induction. To convert electrical energy to mechanical work, they require a magnetic field maintained by magnetizing current, which is reactive in nature. Since the current lags the voltage in an inductive circuit, the phase angle $\phi$ increases, resulting in a low power factor ($\cos \phi$).

Key Formulas: $P = VI \cos \phi$ — Active Power; $Q = VI \sin \phi$ — Reactive Power; $\cos \phi = \frac{P}{S} = \frac{P}{\sqrt{P^2 + Q^2}}$ — Power Factor

Key Points: Induction motors are essentially variable air-gap transformers.; The magnetizing component of current ($I_m$) is responsible for the lag.; Low power factor increases $I^2R$ losses in the transmission and distribution lines.; Synchronous motors can be over-excited to provide leading reactive power for compensation.

Advantages: Improved voltage regulation; Increased system capacity; Reduced penalty charges from utility companies

Disadvantages: High current for same active power load; Increased copper losses in lines and transformers; Requires larger cross-section cables

Applications: Industrial drives; Compressors and pumps; Conveyor systems

Additional Info: Power factor is the ratio of real power to apparent power.. Option B (Synchronous motors) can act as power factor correctors (Synchronous Condensers) when over-excited.. D.C. motors do not affect power factor in the same way as AC inductive loads because they do not rely on a rotating magnetic field generated by AC excitation.. Single phase induction motors also cause low PF but are not as significant as large industrial 3-phase induction motors.

Answer: A is correct — Induction motors are highly inductive loads that consume large amounts of lagging reactive power, thereby reducing the system power factor.

Exam Tip: Always remember: Over-excited synchronous motors are used to improve power factor, while induction motors are the primary cause of low power factor.

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