Active power, reactive power and apparent power are key parameters for generator selection, parallel operation and power distribution design. Their relationship governed by power factor directly affects generator safety, service life and operation efficiency.

1.Definition of Three Types of Power

Reactive Power (Q, Unit: kvar)

Apparent Power (S, Unit: kVA)

2. Mathematical Relationship & Power Factor

①S²=P²+Q²

②P=S×cosφ

③Q=S×sinφ

The closer cosφ is to 1, the less reactive power and lower operation loss.

Standard rated power factor for generators is 0.8.

Low power factor leads to excessive current and overload risk.

3.Practical Case: 100 kW Generator

Rated state (cosφ=0.8): S=125 kVA, Q=75 kvar, all parameters within safe range.

Poor power factor (cosφ=0.7, P=100 kW): Actual S=142.8 kVA, 14.2% overload. Winding current surges, temperature spikes and insulation ages rapidly.

4. Hazards of Long-Term Full Load with Low Power Factor

Stator winding damage: Copper loss rises with the square of current. Continuous high temperature cracks insulation and causes short circuits.

Excitation system failure: Extra reactive load overworks AVR and excitation windings, resulting in unstable voltage or loss of magnetism.

Poor power quality: Severe voltage and frequency fluctuation may damage electrical equipment.

Unexpected power outage: No spare capacity for sudden heavy loads, triggering overload protection and emergency shutdown.

5. Standard Safe Operation Rules

Optimal long-term load rate: 60%–80%

Long-term 100% full load operation is prohibited

Temporary overload limit: ≤110% within 1 hour (only for emergency standby)

Reserve over 20% extra capacity to offset reactive loss and sudden load shocks