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.

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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 star