Resist or React:

The Case for Reactive Load Bank Testing for Stationary Engines

by Keith Watkins and Daniel Williams
Peterson Power Systems

For years, responsible facilities managers have been aware of the need for backup electric power generation equipment at their businesses as “insurance” against threats such as lost time and damage to equipment due to interruption of utility power. Backup generators, and the testing and maintenance associated with their operation, represent a substantial portion of any facility manager’s defense against these threats, but many managers (and some equipment and service providers) remain unaware of their power generation equipment’s real-world weaknesses due to incomplete testing procedures of their equipment—when utility power fails at their facility, the lights go out.

This paper will explain the importance of addressing a facility’s emergency power generation system as a whole in order to identify system-wide weaknesses, and will address and explain the difference between resistive and resistive/reactive load bank testing, and why the latter is necessary. Finally, this paper will address the importance of choosing a knowledgeable and experienced service provider as a partner in preparing a facility-specific emergency power generation maintenance and service plan.

Stationary Engines: Greater than the Sum of their Parts

Any given emergency power generation unit is actually a complex system, or series of systems, working together to perform several duties at once: at the system’s “heart” is the “prime mover”, which burns fuel to create movement, which is in turn converted into electricity as the generator operates. However, various discrete systems and subsystems in the unit make this possible: alternators, regulators, switchgear, and various other additions to generation systems all contribute to a given system’s operation. These additional components can be products of various manufacturers, and are usually designed to interface with a number of makes, models, and sizes of diesel generators. Like any other mechanical or electrical component, all are subject to failure, and have varying maintenance needs; all must be tested and serviced.

Test the System, Not Its Components

Despite the inconveniences it represents, only a complete system-wide test will provide an accurate picture of how a facility’s emergency power generation equipment will perform during an interruption in utility power, particularly in the actual conditions under which the system will operate.

Resistive Testing: Only Part of the Story

Generally, in any facility, the only equipment operating on a resistive load are its incandescent lights and electric heaters2; these units draw a steady supply of electricity from a generator, but do not produce the large block loads that truly test a generator’s performance. A resistive load test will verify that a generator’s prime mover is working, but it will not identify how well it will actually perform when stressed with an actual emergency need and the reactive load pattern. Brownouts, blackouts, hurricane storm surges, strong winds, ice storms, tornados, and grid interruptions can all disrupt utility power supply to a facility, and resistive-only testing simply cannot simulate the actual conditions in which the facility’s equipment will operate.

The Case for Continued Testing

A proper resistive/reactive test of a system’s complete performance, with help from a knowledgeable service provider, is a facility manager’s only means of truly verifying that his system will operate to an acceptable standard during an emergency. Only after observing and rating a system’s performance, and proving that its various components are able to operate in synch and produce power for a sustained period under the specific stresses produced by his facility, can a facility manager know with confidence that his business is safe from the various threats posed by a sustained interruption of utility power service. However, a proper service regimen doesn’t end there. Like all modern electric systems, emergency power generation equipment must be tested and maintained at proper intervals, and its individual components must be tested, as well.

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