The selection of diesel generator set for your needs is by no means an easy task.

Purchasing the right diesel generator that fits in your scheme of things is one of the critical aspects that you need to make before investing in one. And the catch here is that your generator should not be underutilized or overloaded.

If you choose a diesel generator that is too large for your power needs then it is a direct expenditure on its purchase, installation, maintenance and repairs including the added fuel cost to run the diesel generator.

If you choose a diesel generator with a lesser power rating then it will not be able to run the essential appliances during a power cut.

Also, overloading the diesel generator will not only lead to its breakdown but also damage the electric appliances.

What happens when the diesel generator gets overloaded?

As a general rule, diesel generators should not be overloaded. When a diesel generator runs for long periods with a rating that is above the maximum rating of the generator set then-

• The diesel engine gets overheated
• Windings off the alternator burn out due to overheating of the alternator
• Engine failure due to the breakdown in oil consistency and low oil pressure
• The lifespan of the diesel generator reduces

Selection of diesel generator set done right

1. Know your power needs-

The size of the diesel generator you require mainly depends on the type of electrical appliances that you intend to run during a power outage. Household appliances need smaller diesel generators whereas industries require a bigger generator to run the machines and heavy equipment.

Anyways, be it for industrial or household purposes, it is always better that you reduce the list of items that you need to run during a power outage to save money on it.

2. Starting load requirements-

The starting load requirements can be a bit complicated. Some appliances that have fans and pumps in them require more power during their initial acceleration startup but then do not consume more power when it functions continuously afterward. The rotor of the motor and the shaft driven load is at a standstill in the initial stage. It requires a greater power supply at the time of acceleration than it does to keep them rotating.

Here, when you have a star-delta starter for the electric motor in your equipment, then you need to multiply three times the motor horsepower to your required steady-state load. When the motor starter is a direct-online (DOL) starter, then the load is obtained by multiplying six times the motor horsepower.

For an inverter or variable frequency drive (VFD) starter, the kick load will be nil and hence there is no need for spare load in the generator.

The diesel generator size also depends on whether you want to run it as a standby power, continuous or a prime power. Standby power is used in residential and commercial complexes when only there is a power outage.

The continuous power generators will be used when there is no grid supply of power usually in remote locations or offshore destinations.

3. Diesel generator sizing calculation-

The first step is deducing the total electric load. After that, the steady state load is established.

Calculate your capacity requirements and this is the maximum power that your generator will need to supply at any given point in time. Work it out by adding up all the electrical loads of the systems and equipment you will need to power at the same time.

One thing that has to be noted is that your future power requirements also need to be taken into account. If your electrical requirements are going to increase or grow in the near future, then select a generator with some spare capacity. But remember that running a diesel generator under its rated load may also damage its engine.

Diesel generators don’t like to run without loads. Don’t attempt to run the diesel generator when you are not using it for at least 75% of its potential load. You will be left with a damaged diesel generator within the warranty period because running on lower loads will cause it to glaze and you will have a major engine repair at hand.

One option when you want to purchase a larger unit with the intent of having a demand at a later stage is to install a dummy load onto the generator. This will ensure that there will be no glazing in the diesel generator. Talk to your diesel generator dealer about this condition and take their opinion on your future power needs and its solutions.

Note: A diesel generator should not run for more than 80% of its load for prolonged periods when used as a standby power mode and this is done to ensure the longevity of the engine and to reduce the maintenance costs. Also, a diesel generator should not run at less than 60% load for longer periods to prevent the engine from glazing resulting in engine failure.

4. Selection of diesel generator set (How to size a diesel generator?)-

When you add up all the maximum required power wattage for your equipment you will get the summation of the power requirement in kilowatts (kW). Generators are generally rated in kVA (kilo-Volt- Ampere) that is the apparent power or the amount of power in use in a system. When there is a cent percent efficient system, kW=kVA.

But the electrical systems are never 100% efficient and so there is a need for the kW to be converted to kVA by multiplying electrical efficiency known as the power factor. International standard rate diesel generators have a power factor of 0.8. Hence the power rating of your generator is derived by dividing the total power required in kW by 0.8.

The resultant obtained thus is in kVA and that is the generator rating that you would require for your power solution needs.

kW to kVA Conversion kW / 0.8 (Power Factor) = kVA  Example: 100 kW / 0.8 = 125 kVA

Once you are done with the load calculations and you know your requirements for the diesel generator, get in touch with your local diesel generator dealer. They are the best people to advise you on your power solutions. They fully understand the technicalities involved and suggest you the best possible make for your power needs.

Anyways, the dealer will get a load test done to get the required kVA rating to allow for sizing to be done correctly for the first time.

There are other factors also that determine the size of the diesel generator you purchase. Those are-

Environmental factors-

The environment is also responsible for the proper functioning of the diesel generator. Alterations in humidity and temperature partly influence the working reducing the power capabilities of the diesel generator.

Physical Installation-

Proper cooling and exhaust airflow provision must be considered when purchasing a diesel generator. Inadequate airflow can sometimes lead to complete generator failure.

Once you are done with the settling of key points, you will have good knowledge and thus be able to decide on your selection of diesel generator set. If you have any further questions get it clarified with your local diesel generator dealer and purchase one with their guidance for your power needs.