Testing of On-Site Power Systems Improves Reliability

February 04, 2016

Periodic load bank testing is a smart practice at facilities and campuses that either must have (by code) or want reliable on-site backup power. It can be a key component in a comprehensive preventive maintenance plan for a backup power system.

A load bank is a device that provides a direct electrical load to a generator that is equal to the load the generator is expected to handle when primary power is unavailable. It facilitates testing the generator without having to transfer the load to the backup generator. This manner of testing, which does not disturb the normal power, avoids any risk of disruption of business as usual or protracted downtime if there is a failure.

Load bank testing verifies that the backup power system is capable of responding when called upon. It helps ensure proper operation of the gen-sets, the automatic transfer switch, the UPS, and other components. The testing may also be required to meet state and federal regulations (such as from the NFPA) and whatever other system verification is required.

The testing also helps identify developing problems that, if unaddressed, could lead to damage of equipment or failure of the backup power system.

Load banks may be stored on-site (either permanently installed or, if portable, wheeled out of storage and into place during the testing) or trucked in temporarily for the length of the testing. There are many reliable load bank rental companies that will truck in trailer-mounted equipment in the voltage and capacity called for, run the test, and record the results, perhaps utilizing software that works in conjunction with the load banks used in the testing.

Some codes require load bank testing yearly, an interval that may suffice as a best practice at many facilities. However, at facilities where uninterrupted power is required by code, such as hospitals; code compliance may require load testing monthly to validate performance of the complete system.  This includes generator set and automatic transfer switches, with a load that simulates actual loads. At other types of facilities, where the importance of uninterrupted power is driven by business needs, such as data centers; testing should take place regularly.

Periodic load bank testing of a diesel powered generator provides proof that the electrical generation system(s) can support a full load by maintaining design voltage and frequencies; validates uninterruptible power supply (UPS) operational performance and battery autonomy; and can uncover system defects that have developed since installation and the initial testing.

It can also prevent wet stacking and carbon buildup of unburned fuel and soot in the exhaust system that can occur when a diesel engine is not used regularly, runs only light loads for extended periods of time, or runs for extended periods of time at less than the designed operational temperature. Running the generator at the required percentage of rated load can help preclude wet-stacking by burning off carbon deposits in the engine, minimizing the need for a major engine overall to address that buildup.

Load bank testing can also monitor the engine for fuel consumption and leaks, operating temperature, oil pressure, kW load, AC voltage and frequency, and other parameters. If readings are not as expected, the technician conducting the testing can disconnect the load and take note of any problem that would require attention at a non-critical, rather than critical time.

Record keeping is an important component of load bank testing. When testing a backup generator under a live load, load details such as time of day, weather, building under normal use or unoccupied, can be documented. Data logging software used during the testing enables comparing baseline data with evolving data to determine if the generator is still capable of performing at the original designed-in level. The reports (electronic and hard-copy) may indicate performance changes useful for trending and analysis as well as for early diagnoses. Electronic reports can be networked to critical power management or to building management systems.

SIGMA LT Load Controls facilitate consistent and reliable testing for resistive load banks at facilities of various sizes. Both local and hand held remote controls are available.

SIGMA LT Load Controls can be used for stand-alone and daisy chain load tests, linking up to 25 individual load banks. The controls, which support full 3-phase instrumentation, can accept and reject a load from individual load banks. The local control features electronically controlled push buttons while the remote control features a sleek touch screen interface for simple load selection and individual load bank control and monitoring. The SIGMA LT remote control has USB capability and supports transfer of data on a USB stick for analysis.

The load controls work with SIGMA LT Basic software that runs on Windows tablets and PCs. The software, which has a multi-language interface, helps streamline the testing process and provides graphical, chart and individual load test views. It also offers rich reporting capabilities.

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