A load bank is a crucial part of any industrial or commercial site’s power system, ensuring the quality and reliability of the site’s power source by allowing testing and verification, calibration and adjustment, and it is important to understand exactly what they are and how they work.
In this article I will explain just what a generator load bank is, how it works and how the four basic types of load banks differ.
What Is A Load Bank For A Generator?
A load bank is a piece of electrical equipment used to test, calibrate and adjust a site’s generator, to verify its output and to keep a generator in proper running condition.
Usually large in scale, load banks provide a specific load to a generator – that is, they simulate the electrical load, or the power requirements and power draw, of a site and its normal operation.
A load bank connects to the output of a power generator, and provides that generator with electrical factors similar to what the generator would see when providing power in normal operations, in order to determine that the generator is operating properly.
In addition to testing and verification, load banks can also be used for adjustment and calibration of the generator.
A load bank is generally required to do periodic adjustment and verification procedures on a site’s main power supply, and is also important in regularly testing backup generators, which may be left not running for long periods of time. Typically both external (like from the National Fire Prevention Association) and internal regulations require regular use of a load bank, but often the prime motivation for their use is the often enormous savings in money they provide by ensuring continuous power and preventing downtime.
Another basic function of load banks is in power systems where supplemental renewable power sources, such as solar, hydro or wind power, are used, to absorb extra power that normal operations can’t utilize. They are also used to reduce “wet stacking” (the accumulation of fuel in the exhaust systems of diesel generators), to allow any type of backup generator to be run periodically with normal loads, to factory test newly manufactured generators, to optimize loads in complex power systems and for many other specialized tasks.
A load bank must do something with the power it receives from the generator, and the most common type of load banks will incorporate a large resistor or bank of resistors, which convert the electrical power into heat, which is then dissipated by the load bank’s forced air or forced water cooling system.
The Four Types Of Load Banks
Resistive Load Bank
Resistive load banks are the most common type in use. They consist of a large electrical resistor which supplies a simple load to the generator, thereby applying load to the entire generator chain, including the prime mover (the generator’s engine or turbine) and the gas supply.
Resistive load banks use electrical resistance, often in the form of grid resistors, to convert the generator’s electricity into heat, which then needs to be cooled using water or air in either forced or convection cooling systems.
Most typical resistive load banks are portable, but they can be installed permanently, and often are kept at sites where power supply is critical, or where backup generators are periodically employed.
Resistive load banks are most often for AC power, but special units for testing DC generators are also available. The AC units provide unity (in phase) power loads, and are often supplemented by inductive and/or reactive load banks (see below) for lagging or leading power factors respectively.
Inductive Load Bank
An inductive load bank uses an iron core reactive element to simulate a lagging power factor load (a load where current and voltage are out of phase, with current lagging behind voltage).
Inductive load banks are important in testing and calibrating generators at sites where there may be a predominance of lagging power devices, such as HVAC systems, lighting and industrial motors.
Inductive load banks are often used in conjunction with resistive load banks, and typically will provide 75 percent of (lagging) inductive load to 100 percent of (unity, or in-phase) resistive load, though the lag factor of some inductive load banks can be adjusted.
Capacitive Load Bank
Capacitive load banks are similar in concept to inductive load banks, but instead of providing a lagging power load, a capacitive load bank uses industrial capacitors to simulate a leading power factor, where current and voltage are still out of phase, but current leads voltage.
Capacitive load banks are most often utilized in operations where there is a predominance of electronic equipment, like telecommunications equipment, computer systems, testing and calibration apparatus and the like.
Resistive Reactive (Combined) Load Bank
Not exactly a different type of load bank, the resistive reactive load bank provides both resistive elements and inductive elements, thereby combining the first two types of load banks.
A resistive reactive load bank allows testing, verification and calibration of generators at 100 percent capacity – both full kVA (kilovolt-ampere) and kW (kilowatt) nameplate rating in non-unity (lagging) power factor scenarios.
A resistive reactive load bank can normally be used in pure resistive mode, pure inductive mode, or in combination, with the ability to adjust the lagging factor. Sometimes a combined unit might include resistive, inductive and capacitive load banks.