The three most common types of load banks are resistive, inductive, and capacitive. Both inductive and capacitive loads create what is known as reactance in an AC circuit.
Reactance is a circuit element's opposition to an
alternating current, caused by the buildup of electric or
magnetic fields in the element due to the current and is the "imaginary" component of impedance, or the resistance to AC signals at a certain frequency. Capacitive reactance is equal to 1/(2⋅π⋅f⋅C), and inductive reactance is equal to 2⋅π⋅f⋅L. The unit of reactance is the
ohm. Inductive reactance resists the change to current, causing the circuit current to lag voltage. Capacitive reactance resists the change to voltage, causing the circuit current to lead voltage.
Resistive load bank A resistive load bank, the most common type, provides equivalent loading for both
generators and
prime movers. 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-power 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. The most common type uses wire resistance, usually with fan cooling, and this type is often portable and moved from generator to generator for test purposes. Sometimes a load of this type is built into a building, but this is unusual. Rarely a
salt water rheostat is used. It can be readily improvised, which makes it useful in remote locations. For testing
automotive batteries, a carbon pile load bank allows an adjustable load to be placed on the battery or charging system, allowing accurate simulation of the heavy load on the battery during cranking of the engine. Such devices are usually portable and may include metering to show voltage and current.
Inductive load bank An inductive load includes inductive (lagging
power factor) loads. An inductive load consists of an iron-core reactive element which, when used in conjunction with a resistive load bank, creates 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. An inductive load is used to simulate a real-life mixed commercial loads consisting of lighting, heating, motors, transformers, etc. With a resistive-inductive load bank, full power system testing is possible, because the provided impedance supplies currents out of phase with voltage and allows for performance evaluation of generators, voltage regulators, load tap changers, conductors, switchgear and other equipment.
Electronic load bank An electronic load bank tends to be a fully programmable, air- or water-cooled design used to simulate a solid state load and to provide constant power and current loading on circuits for precision testing. ==Railways==