Load bank


Load bank

A load bank is a device which develops an electrical load, applies the load to an electrical power source and converts or dissipates the resultant power output of the source.

The purpose of a load bank is to accurately mimic the operational or “real” load that a power source will see in actual application. However, unlike the “real” load, which is likely to be dispersed, unpredictable and random in value, a load bank provides a contained, organized and fully controllable load.

Consequently, a load bank can be further defined as a self-contained, unitized, systematic device that includes load elements with control and accessory devices required for operation.

Whereas the “real” load is served by the power source and uses the energy output of the source for some productive purpose, the load bank serves the power source, using its energy output to test, support or protect the power source.

Applications

Load banks are used in a variety of applications, including:

* Factory testing of engine diesel generator sets
* To reduce wet stacking problems
* Periodic exercising of stand-by engine generator sets
* UPS system testing
* Battery system testing
* Ground power testing
* Load optimization in prime power applications
* Factory testing of turbines
* Remove carbon build-up on the piston heads

Types of load bank

The three most common types of load banks are resistive load banks, reactive load banks, and capacitive load banks.

Resistive load bank

A resistive load bank, the most common type, provides equivalent loading of both generator and prime mover. That is, for each kilowatt (or horsepower) of load applied to the generator by the load bank, an equal amount of load is applied to the prime mover by the generator. A resistive load bank, therefore, removes energy from the complete system: load bank from generator—generator from prime mover—prime mover from fuel. Additional energy is removed as a consequence of resistive load bank operation: waste heat from coolant, exhaust and generator losses and energy consumed by accessory devices. A resistive load bank impacts upon all aspects of a generating system.

The “load” of a resistive load bank is created by the conversion of electrical energy to heat via high-current resistors such as grid resistors. This heat must be dissipated from the load bank, either by air or by water, by forced means or convection.

In a testing system, a resistive load simulates real-life resistive loads, such as incandescent lighting and heating loads as well as the resistive or unity power factor component of magnetic (motors, transformers) loads.

Reactive load bank

A “reactive” load includes inductive (lagging power factor) and/or capacitive (leading power factor) loads.

Inductive loads, the more common type, consist of iron-core reactive elements which, when used in conjunction with a resistive load bank, create a lagging power factor load. Typically, the inductive load will be rated at a numeric value 75% that of the corresponding resistive load such that when applied together a resultant 0.8 power factor load is provided. That is to say, for each 100 kW of resistive load, 75 KVAR of inductive load is provided. Other ratios are possible to obtain other power factor ratings. Inductive loads are used to simulate real-life mixed commercial loads consisting of lighting, heating, motors, transformers, etc. With a resistive/inductive load bank, full power system testing is possible, given the impact of reactive currents on generator/voltage regulator performance as well as effects on conductors and switchgear.

Capacitive load bank

A capacitive load bank is similar to a reactive load bank in rating and purpose, except leading power factor loads are created. These loads simulate certain electronic or non-linear loads typical of telecommunications, computer or UPS industries.

Railways

Where a diesel-electric locomotive is equipped for dynamic braking, the braking resistor may be used as a load bank for testing the engine-generator set.

See also

* Dummy load
* Grid resistor


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