Understanding Diesel Generator Specifications: kW, kVA and Power Factor

Diesel gensets supply backup power for businesses, medical facilities, and builders during power outages. In other scenarios, diesel generators are the only power sources in areas across the globe. These areas do not have adequate grid coverage. They include remote oil fields, distant farming facilities or isolated mining operations. Choosing the right generator for the job requires an understanding of technical specifications which this blog will help provide.

When a diesel generator is operating under proper conditions, it will run on high efficiency and enjoy a long service life. In order to ensure this investment is the perfect machine for the job, a buyer should understand the relationships between kilowatts (kW), kilovolt-amperes (kVA) and power factors (PF).

• Kilowatts (kW) measure the real electric power supplied by the diesel generator. This power is used by the equipment and appliances within the building.
• Kilovolt-amperes (kVA) measures the apparent power of the diesel generator. 
• The power factor (PF) is the ratio between real power and apparent power. For example, if a building consumes 1900 kW and 2000 kVA, the power factor is ~90%.

On the diesel generators nameplate, you’ll find the kW, kVA and PF values. The operating conditions of the generator are determined by the connected load rather than the unit itself.
It is recommended that you utilize a professional electrical engineer to provide proper unit sizing for your new or used diesel generator investment.

The diesel engine capacity is the limiting factor in the maximum kW output a diesel generator can provide. If the kW and kVA stay below their rated values, a diesel generator can exceed its rated power factor. We don’t recommend going below the rated power factor as the diesel generator will not operate as efficiently. The generator can be damaged if the kW or the kVA rating is exceeded.

It’s also important to understand how the leading and lagging power factor affects diesel generators. When the generator’s voltage is ahead of the current, the electrical load has a lagging power factor. This type of load behavior is called inductive which encompasses transformers and electric motors. If the current is ahead of the voltage, the load is experiencing a leading power factor. This type of load behavior is called capacitive which encompasses capacitor banks and batteries.
 
Many buildings you see in everyday life have more inductive loads than capacitive loans. That means the power factor is typically lagging. Diesel generators were designed for this specific load type.
In instances where buildings have capacitive loans, the generator voltage can become unstable with a leading power factor. This phenomenon will trigger automatic protections thereby disconnecting the diesel generator from the building. For these reasons it’s important to consult with an experienced electrician or engineer to understand the specific generator requirements your building may need. 

Contact Generator Source today for all your new or used diesel generator needs! We’ve been in business for 40 years and have the experience, support, and team of professionals to meet your generator needs.

Story Summary

What is the difference between kW and kVA?

• kW (kilowatts) measures the real electric power supplied by the generator that is used by equipment and appliances.
• kVA (kilovolt-amperes) measures the apparent power of the generator, which includes both real and reactive power.

What is power factor (PF)?
Power factor is the ratio between real power (kW) and apparent power (kVA). It indicates how efficiently the generator's power is being used. A higher power factor means more efficient power usage.

What is a typical power factor for diesel generators?
Most diesel generators have a power factor of 0.8, meaning 80% of the apparent power is converted to usable real power.

How do you convert between kW and kVA?
To convert kVA to kW: kW = kVA x power factor
To convert kW to kVA: kVA = kW / power factor

What limits a generator's maximum output?
The diesel engine capacity limits the maximum kW output. The generator windings limit the maximum kVA output.

Can a generator exceed its rated power factor?
Yes, a generator can exceed its rated power factor as long as the kW and kVA ratings are not exceeded. However, operating below the rated power factor reduces efficiency.

What is the difference between leading and lagging power factor?
Lagging power factor: Voltage leads current, typical of inductive loads like motors
Leading power factor: Current leads voltage, typical of capacitive loads like capacitor banks

Why is proper generator sizing important?
Proper sizing ensures the generator can handle the required load efficiently without being overloaded or underutilized. This optimizes performance and lifespan.