Standby Power: An Overview of Load Banking

A load bank delivers an artificial load to a standby generator system to test its performance. In particular, it tests the system’s ability to supply power during an outage. The difference between an artificial load and a “real” one is that the former is predictable, and the latter is not. Nevertheless, load banking provides a competent basis for assessing system performance. Diesel generators that perform at less than 30 percent of their nameplate Kilowatt rating at any point during a 30-minute monthly test should be tested each year. Guidelines for yearly testing are found in National Fire Protection Association Code 110 (NFPA 110).

Four Types of Load Banks

Four types of units are used to test generators that power commercial and industrial facilities:

1. Resistive banks, which simulate resistive loads;
2. Inductive banks, which simulate inductive loads;
3. Capacitive banks, which simulate non-linear loads; and
4. Electronic banks, which simulate a solid state load.

The type of testing a generator requires is determined by the characteristics of the load it would carry. In some instances, resistive and inductive banks are featured in one unit – an arrangement that facilitates “full power system testing.” In other cases, two or more units are used to exercise two or more generators located at the same site. Necessary testing should be determined by a careful assessment of a facility’s electrical needs. Prime Power can make this assessment and supply the necessary testing equipment.

Other Uses for Load Banks

In addition to testing the standby power of generators, load banking is also used to:
• remove carbon accumulation from piston rings
• factory test diesel generators
• perform load optimization for prime power installations
• test uninterruptible power supply (UPS) systems
• resolve wet stacking

A common issue in diesel generators, wet stacking occurs when a generator fails to burn all the fuel that enters its combustion chamber, allowing it to collect in the exhaust pipe. Wet stacking can be resolved by operating a generator at 70-80 percent of its nameplate kilowatt rating until the fuel evaporates. In addition to testing generators, Prime Power also specializes in resolving wet stacking.

Buying a Load Bank vs. Outsourcing

Some facilities choose to buy a unit instead of outsourcing to a power services provider – a decision that should reflect how often the unit would be used. For facilities that need a load bank for more than generator testing, onsite implementation may be a sensible choice. But for companies that require only generator testing, outsourcing is usually more cost effective.

Prime Power has the Experience You Need

Load bank testing can be a vital aspect of preparing a facility for a power outage. If the generator in your facility operates at less than 30 percent of its nameplate Kilowatt rating during its monthly test, call Prime Power. For almost 30 years, we have performed load banking for large and small facilities in the commercial and industrial sectors. We also modernize and retrofit generators for code compliance and to increase their fuel efficiency.

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