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Resistive and Reactive Load Bank Testing

Resistive-Load-Bank-Controls.JPGMost 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 issues. To prevent loss of time because loss of utility power, scheduled load testing of backup generators 
is recommended. When testing an emergency generator configuration, the engine, generator and controls systems are tested.

Load bank testers can be used in place of a facilities load. This device develops an electrical load for generator output power. Load banks can be defined as a self-contained, unitized, systematic device that include load elements with control and accessory devices (system that tests emergency generator and associated systems). Resistive and Reactive are the two styles of load bank testing systems available.

This article defines:
  • Resistive Load Bank Testing
  • Reactive Load Bank Testing

Resistive Load Bank Testing

Resistive load bank testers (Figure 2) 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:
  • Lighting
  • Motors
  • Transformers
As the load bank tester is connected directly to the generator output, the tester increases demand,and the generator systems are tested to full capacity:
  • Generator – Voltage and amperage at rated load
  • 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) operate when demanded
This testing will not allow the generator to produce the full Kilo-Volt Amperage (KVA) rating. KVA is absolute value of complex power equations. A volt is considered electrical pressure and an Amp is considered electrical current. KVA is the product of the amperage and voltage.

Figure 2, Resistive Load Bank Testing 

Reactive Load Bank Testing

Reactive load bank testers (Figure 3) 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. A power factor of 1 would indicate 100% efficiency. Most generators run with a power factor of .8 (80%) efficient.

The three types of testers commonly used are:
  • 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.
Figure 3, Reactive Load Bank Testing Equipment
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