Why does power factor improves with capacitor banks in motor circuits?

Power factor improvement with capacitor banks in motor circuits primarily revolves around how capacitors affect the phase relationship between voltage and current in AC circuits.

Here's a detailed explanation:

Understanding Power Factor

• Power Factor (PF) is the ratio of real power (used to perform work) to apparent power (the product of the current and voltage). It is expressed as:

• Inductive Loads like motors introduce a lag in the current waveform with respect to the voltage, which decreases the power factor (makes it more lagging). This lag is due to the magnetic fields within the motor windings that store and release energy, acting somewhat like inductors.

Role of Capacitors

• Capacitors, when connected in parallel to inductive loads, introduce a leading current. This means the current through the capacitor leads the voltage by approximately 90 degrees.

• Cancellation of Reactive Power: 

- Inductive loads consume reactive power, which does not do work but increases the current drawn from the supply, leading to inefficiencies.

- Capacitors supply reactive power back into the circuit, which can cancel out the reactive power consumed by the motor's inductance.

How Capacitors Improve Power Factor:

1. Phase Correction: 

• By adding capacitance, you effectively reduce the phase angle \phi/ by making the total current more in phase with the voltage. This is because:

- The capacitive current leads the voltage, while the inductive current lags it. 

- The combination of these currents results in a net current that is closer in phase to the voltage, thus improving the power factor.

2. Reduction in Line Current: 

• With an improved power factor, the current drawn from the source for the same amount of real power decreases. This is because less reactive current is needed, reducing the apparent power and thus the current for a given voltage.

3. Efficiency and Cost Savings:

• Lower current means less energy loss in transmission lines, less heat in equipment, and often, a reduction in utility bills since many power companies charge based on peak demand and power factor.

4. Practical Considerations:

• Sizing: Capacitors must be sized correctly to match the inductive load of the motor to avoid overcorrection, which can lead to leading power factor issues.

• Location: Placing capacitors at or near the motor reduces losses in the wiring between the capacitors and the motor.

In summary, capacitor banks in motor circuits improve power factor by compensating for the inductive reactance of the motor, bringing the power factor closer to unity, thereby enhancing efficiency, reducing current draw, and potentially saving on energy costs.