Load bank
Encyclopedia
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.
s 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-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.
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.
Sometimes, though rarely now, a salt water rheostat
is employed. Since this type can be readily improvised, it is occasionally used in remote locations.
) 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.
, the braking resistor may be used as a load bank for testing the engine-generator set.
External electric load
If an electric circuit has a well-defined output terminal, the circuit connected to this terminal is the 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 turbineTurbineA turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
s and engine diesel generatorDiesel generatorA diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....
sets - Reduction of wet stackingWet stackingWet stacking is a condition in diesel engines in which not all the fuel is burned and passes on into the exhaust side of the turbocharger and on into the exhaust system. The word "stacking" comes from the term "stack" for exhaust pipe or chimney stack...
problems - Periodic exercising of stand-by engine generator sets
- BatteryBattery (electricity)An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
and UPS systemUninterruptible power supplyAn uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
testing - Ground power testing
- Load optimization in prime power applications
- Removal of carbon build-up on pistonPistonA piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
rings
Load bank types
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 build up 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 generatorElectrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
s and prime movers. That is, for each kilowatt (or horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
) 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
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
.
In a testing system, a resistive load simulates real-life resistive loads, such as incandescent lighting
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
and heating loads as well as the resistive or unity power factor
Power factor
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...
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.
Sometimes, though rarely now, a salt water rheostat
Salt water rheostat
A liquid rheostat or salt water rheostat is a type of variable resistor. It consists of a tank containing brine in which electrodes are submerged to create an electrical load. The electrodes may be raised or lowered into the liquid to respectively decrease or increase the electrical resistance of...
is employed. Since this type can be readily improvised, it is occasionally used in remote locations.
Inductive load bank
A “inductive” load includes inductive (lagging power factorPower factor
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...
) 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.
Capacitive load bank
A capacitive load bank is similar to a inductive load bank in rating and purpose, except leading power factor loads are created, so reactive power is supplied from these loads to the system, hence improves the power factor. These loads simulate certain electronic or non-linear loads typical of telecommunications, computer or UPS industries.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
Where a diesel-electric locomotive is equipped for dynamic brakingDynamic braking
Dynamic braking is the use of the electric traction motors of a railroad vehicle as generators when slowing the Locomotive. It is termed rheostatic if the generated electrical power is dissipated as heat in brake grid resistors, and regenerative if the power is returned to the supply line...
, the braking resistor may be used as a load bank for testing the engine-generator set.
See also
- Dummy loadDummy loadA dummy load is a device used to simulate an electrical load, usually for testing purposes.-Radio:In radio this device is also known as a dummy antenna or a radio frequency termination. It is a device used in place of an antenna to aid in testing a radio transmitter...
- Relative cost of electricity generated by different sources
- Diesel-electric transmission
- Motor-generatorMotor-generatorA motor-generator is a device for converting electrical power to another form. Motor-generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line...
- Three-phase electric powerThree-phase electric powerThree-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...