What is Power Factor?

Understanding Power Factor

Power Factor describes how effectively an alternating-current system uses the electricity supplied to it. The useful portion is called real power and is measured in kilowatts. The total electrical demand is called apparent power and is measured in kilovolt-amperes. A system with a factor of 1.0 converts supplied power into useful work. It needs minimal extra current.

Related glossary terms: Electrical Load Calculation, Line Voltage, Voltage Drop.

Many AC loads don't draw current in step with voltage. Inductive loads include motors, transformers, and some lighting equipment. These loads store energy briefly in magnetic fields. They return part of it to the circuit. This creates reactive powermeasured in kilovolt-amperes reactive. Reactive power doesn't perform useful work. The wiring and electrical equipment still carry its current.

How Power Factor Works, Is Measured, or Is Used?

The basic formula is Power Factor equals real power divided by apparent power. For example, a load uses 8 kilowatts. It draws 10 kilovolt-amperes. Its factor is 0.80. The same load may produce the same mechanical output as a higher-factor load. However, it draws more current from the electrical system.

Electricians and facility technicians measure this value with a power quality analyzer, power meter, or compatible monitoring equipment. The instrument compares voltage, current, and their timing across a circuit. A complete test may also record harmonic distortion, load changes, and phase imbalance. Electronic equipment can create distortion that affects the total result.

Correction usually targets the cause rather than treating the number alone. Capacitor banks can offset inductive reactive power in some motor installations. Active filters or corrected power supplies may suit systems with electronic loads. The correction equipment must match the load, voltage, and switching pattern. It must also match harmonic conditions.

Why Power Factor Matters?

A low factor causes higher current for a given amount of useful work. Higher current increases heating in conductors and transformers. It raises voltage drop and consumes breaker capacity. It also uses capacity in feeders and service equipment. These effects can reduce the additional load an installation can support.

Commercial and industrial utilities may include demand charges or separate requirements tied to low Power Factor. This depends on the rate structure and service agreement. Residential bills more often focus on kilowatt-hours. A low factor may not appear as a separate charge. Even then, the condition can signal an overloaded motor, poor equipment selection, or a power quality issue.

When Power Factor Matters Most?

Power Factor deserves attention in facilities with large motors, compressors, pumps, welders, elevators, or variable-speed drives. It also matters when sizing a service upgrade, generator, transformer, or backup system. A generator rated only by useful kilowatts may not handle the required apparent power. This can happen when the connected factor is low.

Review the measurement under normal operating conditions. Not only when equipment is idle. Compare the result during startup, peak production, and light-load periods. Correction equipment can create problems if it's oversized or switched incorrectly. Problems can also occur without harmonic checks. Installers should also check the available fault current.