Why am I in the dark?
The Importance of Load Bank Testing
The successful operation of a standby power system is the result of careful planning, equipment selection,
installation, and importantly, maintenance. With the need for backup power systems, we also see an increased
need to test those systems to assure that they will perform when called upon to operate. A common feature of
most emergency systems is to provide a system test function to simulate a power failure and start the generator
set. The transfer switch may or may not be arranged to transfer the load to the generator.
Because of concerns about continuity of operation and information loss to these systems the generator set may
run without load. This will allow us to say that the engine did start and produce voltage but without an adequate
load transferred to the generator set we cannot properly exercise the system. Providing load from the building
load may not be practical with sensitive life safety, computer, or communication equipment. Any interruption of
power to these loads may cause a loss of data, operations or jeopardize personal safety.
A load bank can provide the practical means to test the power system without interruption of power to the critical
loads and provides a valuable indication of the overall performance at full load capability. The proper application
of a load bank can prevent loss of capacity and increased maintenance caused by unburned fuel due to wetstacking. Wet-stacking is a common problem with diesel engines which are operated for extended periods with
light loads or no loads applied. When a diesel engine operates without sufficient load it will operate at below its
optimum temperature. This will allow unburned fuel to accumulate, foul the fuel injectors, engine valves and
exhaust system, including turbochargers, and reduce the operating performance.
While wet-stacking is not an issue for gaseous fueled engines it is important to operate them under load to meet
emission standards and seat the piston rings properly to reduce oil consumption and cylinder glazing.
In order for a diesel engine to operate at peak efficiency it must be able to provide fuel and air in the proper ratio
and at a high enough engine temperature for the engine to completely burn all of the fuel. Wet-stacking does not
usually cause any permanent damage and can be alleviated if additional load is applied to relieve the condition. It
can reduce the system performance and increase maintenance.
Load banks are tools used to provide a stable, controllable load for determining performance characteristics of a
power system. Applying an increasing load over a period of time until the excess fuel is burned off and the system
capacity is reached usually can repair the condition. This can take several hours to burn off the accumulated
unburned fuel.
These can be small portable load banks designed to be rolled up to the generator to be load tested or they may
be larger trailer mounted load banks for large generator sets. Since they are used for temporary testing they can
be rented and brought to the generator location. Most portable load banks will include metering and small enough
load steps to test a wide range of generator sizes. They are simple to set up and require only basic operational
instruction. They do require a large supply of fresh air for cooling and must be ventilated to remove the exhaust
heat from the load bank area.
Installed load banks can be provided for larger systems and may be manually or automatically controlled. Many
systems are integrated into building automation systems for monitoring, control and data logging. The load bank
must be designed for the intended voltage, frequency and power capacity. The power handling capacity of the
load bank can be small in the 5 to 10 KW ranges up to many megawatts of power. In addition, some load banks
may include instrumentation for displaying amp, volts, kilowatts or frequency parameters of the system under test.
A common option is an automatic load controller which will monitor the building load and adjust the load bank to
maintain a minimum load on the engine minimizing or eliminating the effects of wet-stacking.
Radiator duct mounted load banks may also be a practical option to provide this supplemental load. These load
banks utilize the engine radiator fan to cool the load elements and can be very effective at providing maintenance
loads for exercising generator sets at a minimal cost.
Today most professional load banks utilize precise resistive elements cooled by an integral fan. Some older load
banks used water or brine filled tanks and a complicated system to raise and lower steel plates into the tank to
vary the load. These primitive load banks are no longer used in common practice due to safety concerns,
maintenance costs and poor load control caused by changes in water temperature, conductivity and level. A
resistive load bank can provide much better control and stability for the testing to be performed and will yield
better quality information about the operation of the generator system performance.
An important consideration may be the emission control equipment provided with the generator set. Many of
these systems utilize catalytic elements which require a minimum operating temperature for efficient emission
control and operation.
In addition the engine will need to be operated according to the manufacturers
recommendations to meet the specified emission standards and permit requirements.
As a manufacturer of load banks used for these purposes we would first recommend that you consult the
manufacturer of the equipment to be tested for their specific requirements. A review of the appropriate
manufacturer recommendations and equipment manuals is important to fully understand the maintenance and
testing requirements. Once the requirements are fully understood a load bank can be practical tool incorporated
into your overall maintenance plan. With the proper selection of equipment installed correctly and maintained
effectively you should not be in the dark when it comes to standby power.
Article provided by Dick Scott with Avtron Loadbank. Call Austin Generator Service at 512-251-2247 for
additional information on load bank testing at your facility.