March 8, 2021

Generator/Genset Load Banking Explained


Having a backup generator is key across various industries. In times of emergency or natural disasters that cause power outages (such as winter storms that Texans experienced in Mid-February 2021), generators can save the day. For instance, businesses can avoid losses, lives saved in medical facilities, and operations can continue running flawlessly in oil & gas or military facilities even after the grid goes off for hours or even days.

However, it can be devastating if your genset fails to operate when most needed. Therefore, you'll want to ensure that you adequately prepare by having emergency and disaster plans in place and genset load banking is a critical part of those plans.

So, What is Generator load banking, and Why Do You Need It?

This is the process that involves reviewing your generator's capabilities to ascertain that it can currently work optimally or as specified by testing it under varying levels of load (using a load bank). The objective or goal is to ensure that your backup genset is continually ready and can reliably & efficiently generate backup power when needed. 

Essentially, standby generators are rarely operated hence the need to perform load banking regularly. Besides, load bank testing helps verify if the genset can still maintain the manufacturer's specified pressure and temperature levels while operating at maximum power rating. It's also essential to note that genset load banking can significantly help cut unnecessary expenses. It can help detect problems earlier that could otherwise have escalated and caused expensive repairs and awful consequences if it fails to run during a critical time.

When Do You Need to Conduct Genset Load Banking

Even if you regularly operate your generator, the routine start-up cannot verify the unit's capabilities, especially if you run at a significantly lower kW rating than the specifications. According to NFPA, the typical rule is that you should execute load banking on any genset that operated at 30% or lower than its kW rating (or any level specified by the manufacturer). Other instances include:

  • When required by law or regulatory bodies, for example, NFPA 110 requires standby generators that are meant to protect the occupants of a commercial building or where genset failure could lead to injuries/deaths to be tested monthly.
  • For businesses where backup generators are to reduce losses, load bank testing can be conducted annually. 
  • When the generator is new or during commissioning to establish the reference point for future working performance.

Types of Load Banks

  1. Resistive

These are the common ones that are used to test prime mover and genset at 100% capacity. It uses resistors that act as loads by converting electrical energy from the generator to heat. Resistive load banks are vital when determining capacity (kW), prime mover controls, and transient response (Hz). However, they're limited in that they can't measure other variables such as kVAR (alternator capacity), alternator controls, load sharing controls, or distribution bus. 

Predominantly, this type of load bank is used with AC voltages, but there are a few uniquely designed resistive DC load banks. Categories that can be tested using resistive load banks include generators with less than 200 kVA rating, portable & small units, and UPS systems.

  1. Reactive

This type makes use of a capacitor or an inductor deployed in the load. The load bank has a working mechanism where electrical waves are converted to magnetic fields. The similarity among the two is that they can test only up to 75% of the power rating. However, capacitor-based reactive load banks can simulate the leading power factor effect, which is common in some electronics or non-linear loads.

Reactive load banks are mainly appropriate for testing motor-driven devices.

  1. Combined Resistive-Reactive Load Bank

The key perk about this type is that it achieves the goal of both resistive and reactive testing to verify the following effectively:

  • Prime mover capacity (kW) and controls
  • Alternator capacity(kVAR) and controls
  • Load sharing controls (kW & kVAR)
  • Distribution bus
  • Transient response in terms of Hertz (Hz) and voltage

The combined load bank is appropriate for gensets as large as 1 MVA (or larger) and single & multiple units.

  1. Electronic

As the name suggests, these use electrical loads to conduct load banking. This is an advanced load bank and produces superior results to the other three. Nevertheless, it's expensive as it can be reprogrammed to test any size and type of generator.

You're better now equipped with all you need to know about genset load banking. If you have any queries about generators, the team at Power System Services can help. We also deal with used and new generators. To learn more, contact us today.