Defining Power Factor in AC Systems
Power factor is a dimensionless quantity in AC (alternating current) electrical power systems, defined as the ratio of real power (kW) to apparent power (kVA). It represents how effectively electrical power is being converted into useful work output. A power factor close to 1 (or unity) indicates high efficiency, meaning most of the supplied power is being used for actual work, while a lower power factor suggests that a significant portion of the current is reactive and not doing useful work.
Components of Electrical Power
In AC circuits, electrical power consists of three components: real power (P), reactive power (Q), and apparent power (S). Real power performs the actual work (e.g., rotating a motor, generating heat). Reactive power is necessary to establish and maintain magnetic fields in inductive loads (like motors and transformers). Apparent power is the total power supplied to the circuit, representing the vector sum of real and reactive power. Power factor (PF) is mathematically expressed as PF = Real Power / Apparent Power, or more fundamentally, as the cosine of the phase angle (φ) between the voltage and current waveforms.
A Practical Illustration of Power Factor
Consider an industrial facility that primarily uses large electric motors. These are inductive loads, meaning they require a significant amount of reactive power. If this facility has a low power factor, say 0.7, it implies that for every 100 kilovolt-amperes (kVA) of apparent power drawn from the utility, only 70 kilowatts (kW) are actually performing useful work. The remaining 30 kilovolt-ampere reactive (kVAR) is reactive power. This scenario leads to higher currents flowing through the system than necessary for the useful work, causing increased energy losses and potentially higher electricity bills due to demand charges for reactive power.
Significance and Applications of Power Factor Correction
A low power factor poses several challenges. It leads to increased current draw for a given amount of useful power, resulting in greater I²R losses (heat losses) in conductors and transformers, voltage drops, and reduced system capacity. Utilities often penalize large consumers for low power factors to encourage efficient energy use and reduce strain on their infrastructure. Power factor correction, typically implemented by installing power factor correction capacitors, aims to reduce the reactive power component, thereby improving the overall electrical efficiency, reducing operational costs, and enhancing the stability and reliability of the electrical network.