Every job and job site demands a dependable power source because insufficient power generation can lead to system failures, equipment damage, or capacity overload shutdowns.
Industrial generator sets, which range from 15kW to over 3 megawatts, require a significant investment, so correctly estimating your power usage needs is critical.
Always consult with a certified electrician before your final decision on generator size. The steps outlined below, however, will help produce the information necessary to make this choice.
Identify the Right Power Rating
First, identify the appropriate power rating for your needs:
- Emergency Standby Power (ESP): The emergency power supplied when the primary power source is unavailable. ESP is the maximum power available for a variable electric load with total yearly operation not exceeding 200 hours.
- Prime Rated Power (PRP): The power provided when commercial power isn’t available or is limited. PRP has an indefinite running time in a variable load setting but no more than 500 hours a year at a 100% load and no more than a 10% overload per 24 hours.
- Limited-Time Power (LTP): The power available during interruptible load curtailment, peak shaving, and situations involving parallel utility operation. LTP is the maximum power a generator can provide for 500 hours a year with no overload.
- Continuous Operating Power (COP): The maximum power provided in a continuous, unvarying load for an unlimited number of hours per year with no overload.
A generator set usually has multiple power ratings on its data plate but may have only a standby or a prime rating.
Your Power Requirements & Generator Size
After determining the applicable rating, calculate your specific power requirements.
1. List the Items Being Powered
Large and small, identify everything which needs to be powered. Are you only running power tools and equipment or will you also have an on-site office with computers, a coffee maker, and HVAC? In addition, consider the entire timeline of a project’s equipment needs, not just what’s required at one or two points along the way.
2. Calculate Starting & Running Wattage
Most powered items have different starting and running wattages. Starting wattage is the initial energy surge required to power something up while running wattage is the power necessary to keep it operating. However, sometimes there will only be running wattage.
For example, a 60-watt light bulb requires, by definition, 60 watts of electricity to light up but requires no additional starting watts to become illuminated. A one-horsepower air compressor requires 1,600 watts to run but almost three times as many watts (4,500) to start. Don’t make the mistake of having a generator which provides enough running power watts, but not enough additional watts for the power surge required to start equipment.
3. Convert kW to kVA
While the total amount of power your equipment requires is measured in kilowatts (kW), generators are rated using kilowatts-volts-amperes (kVA). In theory, kW and kVA should be equal, but no power system is 100% efficient.
Electrical efficiency is measured as a power factor between 0 and 1, with the closer the number is to 1, the more efficient the system.
The international power factor standard for generators is 0.8. Therefore, if you have a total power load of 200 kW, divide that by 0.8 to determine the total generator output you need: 160 kVA. And, to err on the side of caution, a good rule of thumb is to add another 10% to your total kW when calculating necessary kVA.
Always work with a certified electrician to determine your exact power needs. However, the steps above will generate information you’ll need to make that generator size decision.
Have questions about your specific power generation requirements? Contact us today for one of our in-house experts to assist you.
