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What is Generator Power Factor: Understanding diesel generators

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Whether you own or are looking to buy a generator, you want your chosen generator to be a reliable backup power source or even your primary power system, so understanding the significance of the power factor is essential. 

The power factor refers to the efficiency with which your diesel generator converts its electrical power into actual power that your appliances or machines can use.

A high power factor means that your generator is very efficient and can meet your power needs more effectively, while a low power factor can cause your generator to waste energy and be less reliable.

We will dive further into this in this article because understanding your power factor will help you optimise your generator’s performance and ensure that it remains a reliable power source when you need it most.

Why is the power factor important for generators?

The power factor is the ratio between real power (kW) and apparent power (kVA). It indicates the total power the generator supplies and how much of that power is useful. The useful power is also known as the active power, while the remaining power is either reactive or apparent power.

The power factor is an important consideration for a generator because it affects its load capacity. The lower your power factor, the lower the generator’s capacity to deliver power to a given load. 

For example, a generator with a power factor of 0.8 can only provide 80% of its rated power. So, if the generator is rated for 100 kVA, it can only provide 80 kW of power. On the other hand, a generator with a power factor of 1.0 can provide full-rated power. 

Most three phase generators have a design power factor of 0.8 where single phase generators often have a power factor of 1. This is designed to protect the alternator, because the engine will stall before the alternator is overloaded.

A load with a low power factor will cause a generator to produce more reactive power and less active power, which limits its capacity to deliver electrical energy. This is why it’s essential to consider your power factor when buying a generator.

A low power factor can negatively affect a generator and the equipment it powers. For example:

  • Reduced generator capacity: If a load has a low power factor, the generator may not be able to deliver its full rated power capacity, which can limit the amount of equipment it can power.
  • Increased fuel consumption: Generator loads with a low power factor may require more fuel to generate the same amount of power, increasing operating costs.
  • Decreased equipment lifespan: Low power factor can cause excessive heating and voltage drops in equipment, reducing lifespan.

There are ways to improve a generator’s power factor, including:

  1. Using capacitors: Capacitors are devices that store and release electrical energy. Adding capacitors to the load such as a power factor correction unit can compensate for the reactive power generated by inductive loads, thereby increasing the power factor.
  2. Adjusting the load: If the load is causing the generator to produce reactive power, then adjusting the load can help improve the power factor. Do this by adding or removing loads, switching loads on and off, or redistributing loads among multiple generators.

Improving a generator’s power factor requires careful system analysis, load characteristics, and other factors, so getting help from an experienced engineer is a good idea. 

By implementing the appropriate corrective measures, it is possible to improve efficiency, reduce costs, and improve system reliability.

What causes leading and lagging power factors?

When the power factor is less than 1, it can be either a leading or lagging power factor.

A leading power factor occurs due to the capacitive load .This frequently occurs in setups with multiple capacitors or other capacitive loads. This would be balanced with inductive reactors to bring the leading power factor back.

A lagging power factor is more common and caused by inductive loads such as motors. Banks of capacitors are used to compensate for lagging power factors.

It is important to note that both leading and lagging power factors can cause problems for generators and the equipment they power. 

For example, a leading power factor can cause over-voltage conditions, damaging equipment. Meanwhile, a lagging power factor can cause voltage drops, damaging equipment and reducing the generator’s capacity to deliver power.

To address these issues, it’s vital to understand the load characteristics and adjust the generator’s power factor accordingly. You can do this using the corrective measures mentioned earlier, such as adding capacitors or adjusting the load.

How to calculate power factor: the power triangle

To calculate the power factor, you need to understand the power triangle

The power triangle is a graphical representation of the relationship between real, reactive, and apparent power. Real power is used to do work, while reactive power is used to create and maintain magnetic fields, and apparent power is the combination of both real and reactive power.

Power Triangle

Using the power triangle, you must measure the generator’s voltage and current to calculate the power factor. Then, you can use the following formula:

Power factor = Real power ÷ Apparent power

Real power can be calculated by multiplying the voltage and current by the power factor and the load in kW. Reactive power can be calculated by multiplying the voltage and current by the power factor and the load in kVAR.

Once you have these values, you can plot them on the power triangle. The real power is represented on the horizontal axis, the reactive power on the vertical axis, and the apparent power is the triangle’s hypotenuse. The angle between the real and apparent power is the power factor angle.

Using the power triangle to calculate the power factor can determine how efficiently your generator operates. For example, a power factor of 1.0 means that all the power generated is being used for work, while a power factor below 1.0 means that some power is lost in heat or magnetic fields. Therefore, a lower power factor can reduce the energy efficiency of your generator and cause it to operate less efficiently.

It’s essential to understand the power needs of your load and select the appropriate generator for the job to stay within the rated power factor.

Know your overall power factor.

Whether diesel generators are used to provide backup power or as the primary power source, it’s important to either understand the power factor formula yourself or get a qualified engineer to help. 

If you have any questions about your existing generator or buying a new one, contact Solent Power

Paul Phelps Solar Power Owner
Paul Phelps
Paul is the MD of Solent Power and specialises in emergency power solutions, helping to protect your facilities from power loss. Get in touch with us today to discuss the different power brands that we can offer and how they can suit your needs.
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