What is the Power Factor in a Generator?

Power factor is one of the most critical aspects of buying a generator. It is a measure of efficiency and directly affects how much usable power the generator can deliver to your equipment.

At Vital Power, we supply a wide range of generators – from portable suitcase generators to industrial diesel generators, ensuring you get the right power for your needs.

What Affects Power Factor?

Generator power is split into active usable power (kW), and reactive power (kVAR). Some equipment, such as motors, coils, or transformers, requires reactive power. This type of equipment draws reactive power, causing the current to lag behind the voltage. This forces the generator to work harder without increasing the usable power output.

The lower the power factor, the more of the generator’s capacity is tied up managing reactive power rather than powering equipment.

How Do I Know if My Generator has a Low Power Factor?

There are several signs that a generator has a poor power factor.

• Low Power – generator seems underpowered and struggles to run the expected load.
• Tripping Out – increased current flow can overload circuits and cause frequent breaker trips.
• Overheating – excess current caused by low power factor causes overheating cables, connectors and distribution boards.
• Voltage Drops – unstable voltage leads to weak performance that can cause slow startup and uneven power.
• Higher Fuel Consumption – the generator has to work harder to deliver the same amount of usable power.
• Excessive Noise or Vibration – caused by the generator working harder to compensate for reactive power demand.

Power Factor Correction

Power Factor Correction (PFC) is a technique used to improve the efficiency of an electrical system. By using capacitors or other devices to create reactive power locally, the inductive loads that lower generator capacity are counteracted. PFC is important because it can increase usable power output, reduce heat and wear, improve efficiency and support voltage stability.

• Inductive loads cause the current to lag behind the voltage.
• Capacitors are added to create a leading current.
• The two offset each other, improving overall power factor.

Improving a generator’s power factor requires careful system analysis, load characteristics and other diagnostics so it’s advisable to get help from a qualified engineer.

We perform load bank testing as part of our generator service and maintenance programmes. Load bank testing tests and corrects a systems’ power factor, which is crucial for ensuring generators and other equipment operate efficiently.

Why is Power Factor Important?

Power factor shows how much of the power a generator produces is actually usable. The usable part is known as active power, and the rest is made up of reactive or apparent power.

Most three-phase diesel generators have a standard power factor rating of 0.8. This means the generator can deliver 80% of its total apparent power (kVA) as real power (kW).

A 100kVA generator at 0.8 power factor supplies only 80kW of usable power.

A low power factor means the generator is operating inefficiently, leading to wasted energy, increased fuel consumption and higher operational costs.

How To Calculate Power Factor

Power Factor = Real Power (kW) / Apparent Power (kVA)

You can find apparent power by checking the generator’s nameplate or manual. Almost every generator lists its’ kVA rating here. Then use a wattmeter to calculate real power and insert the figures into the formula above.

Whether your generator is being used for backup power or as the primary power source, understanding the power factor will ensure you get the most from your investment. Vital Power can calculate your power factor – contact the experts now.