Sizing an Industrial Generator: The Ultimate Guide
Step 1: Determine the Generator Purpose
Before diving into the nitty-gritty of generator sizing, it is essential to determine the purpose of the generator. Generators are generally classified into two categories: standby and prime applications.
Standby generators provide backup power during utility outages, ensuring business continuity and minimizing downtime. These generators are designed to work for short periods. By definition, standby generators can run for the duration of a power outage: whether it is 5 min, 5 hours, or 5 days.
Prime generators, on the other hand, are used as the primary power source in locations where utility power is unavailable or unreliable. They are built to operate continuously or for extended periods, making them ideal for remote sites or off-grid applications.
Step 2: Identify Power Requirements
Once you’ve determined the purpose of the generator, it’s time to assess your power requirements. Make a list of all the equipment requiring power, including lighting, HVAC, computers, and machinery, etc. It’s essential to consider the types of loads your generator will be handling:
Resistive loads: These are loads that don’t change their power factor, such as lighting and electric heating.
Reactive loads: These loads have inductive or capacitive components, such as transformers, motors, and capacitors. Reactive loads can cause voltage fluctuations, making generator sizing more complex.
Non-linear loads: These loads generate harmonic currents that can distort the generator’s output waveform, causing overheating and reduced efficiency. Examples of non-linear loads include variable frequency drives (VFDs), uninterruptible power supplies (UPS), and computer equipment.
Step 3: Understand Motor Starting Methods
Motor starting methods can significantly impact the size of your generator. There are three common starting methods:
Across-the-line (ATL) starting: This method applies full voltage to the motor, resulting in high starng currents. DOL starting requires a larger generator to handle the inrush current.
Star-delta starting: This method reduces the starting current by connecting the motor windings in a star configuration during startup, then switching to a delta configuration for normal operation. Star-delta starting requires a smaller generator than DOL but may not be suitable for all motor types.
Soft starters and variable frequency drives (VFDs): These electronic devices control the motor’s voltage and frequency, allowing for a gradual increase in speed and minimizing inrush currents. They require a smaller generator but can produce harmonics that may necessitate additional sizing considerations.
Step 4: Consider Environmental Factors
Environmental factors play a crucial role in generator sizing. High altitudes, extreme temperatures, and high humidity can affect the generator’s performance, necessitating a larger unit. Consult the generator manufacturer’s guidelines for derating factors to account for these environmental conditions.
Step 5: Choose a Fuel System
The choice of fuel system can impact the size and overall efficiency of your generator. Common fuel options include diesel, natural gas, and propane. Each fuel type has its advantages and disadvantages in terms of cost, availability, and environmental impact. Consider your specific needs, location, and budget when selecting a fuel system for your generator.
Step 6: Calculate Your Generator Size
Now that you’ve gathered all the necessary information, it’s time to calculate the size of the generator you need. Start by adding up the total power requirements of all the equipment you need to power. Remember to account for the types of loads, motor starting methods, and environmental factors.
For standby generators, it is essential to include a safety margin in your calculations. This ensures that your generator can handle unexpected load increases or future expansion. A general rule of thumb is to add 20-30% to your total power requirements.
For prime generators, consider the generator’s continuous power rating, which is the maximum power it can produce for an extended period. Ensure that your generator can handle the peak load requirements while maintaining a safety margin.
Finally, consult with a generator manufacturer or specialist to verify your calculations and help you choose the right generator for your needs.
Conclusion
Sizing an industrial generator does not have to be complicated. By following the recommended procedure for generator sizing in standby and prime applications, considering environmental factors, fuel systems, types of loads, and the impact of motor starting methods, you will be well on your way to selecting the perfect generator for your specific needs.
Keep in mind that this guide is meant to simplify the process and provide a general understanding of industrial generator sizing. For a more accurate and detailed assessment, always consult with a generator specialist or manufacturer before making a final decision.
Please call your Kinsley Power Systems representative at 800-255-3503 to schedule a sizing consultation or CEU-eligible class.
For additional help, Kohler Generator Sizing tool.