Most generator manufacturers load test generators as a part of the manufacturing process. Shipping, installation and installation design (to include paralleling of emergency generators) can provide un-planned machinery issues. To insure generator provides power when utility power is lost, load testing the generator is recommended.
When testing an emergency generator configuration, the engine, alternator and generator control systems are tested.
Load bank testers can be used in place of a facilities load. This device develops an electrical load for the generator. Load banks can be defined as a device that represents a load to the generator. Resistive and Reactive are the two styles of load bank testing systems available.
Resistive Load Bank Testing
Resistive load bank testers are the most common type of the two styles of load bank testers. The load of the resistive load bank is created by the conversion or electrical energy to heat by use of high power resistors (grid resistor configuration often used). The resistive load simulates loads such as:
- Incandescent light bulbs
- Heating elements such as space heaters or hot plates.
The load bank tester is connected directly to the generator output. The operator increases the resistive load by energizing load step switches until the prime mover is at capacity. Examples of generator systems tested are:
Reactive Load Bank Testing
- Enclosure Louvers – Opens when enclosure temperature reaches rated temperature.
- Engine Fuel System – Insures engine fuel system functions while fully loaded.
- Engine Cooling System – Coolant temperature can be monitored under actual generator load.
- Engine Air Intake System – Insures air intake system (louvers can be included) are capable of proper supply.
Reactive load bank testers are used to test the engine generator at its rated power factor. Power factor is the measure of how efficiently the load (current) is being converted into useful work output. It is a good indicator of the effect of the load (current) on the efficiency of the generator.
The construction of testers commonly used are:
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- Resistor - Resistors are connected in banks. Each bank is energized to simulate linear load to the generator.
- Inductive – The major component in this tester is an iron core reactive element. When used in conjunction with a resistive load tester creates a lagging power factor load (current out of phase with voltage). Used for loads consisting of lighting, heating, motors, transformers etc.
- Capacitive – The major component in this tester is the capacitor bank. The operation principle is similar to the inductive system. The dielectric material in the capacitors change the power factor to a leading power factor. The load provided by this unit simulates electronic or non-linear loads typical of telecommunications, computer or UPS (Un-interruptible Power Supply) industry.
- Electronic Load Bank – Fully programmable, air or water cooled design. These testers are used to simulate a solid state load and provide constant power for precision testing.