Part of every significant construction project and major renovation should be the commissioning of the electrical systems (or recommissioning for renovations) along with the heating, ventilating and air conditioning (HVAC); mechanical; fire alarm; and other systems in the facility. Two excellent sources for information about commissioning are the National Fire Protection Association (NFPA) 70B Recommended Practice for Electrical Equipment Maintenance (2010 Edition) and U.S. General Services Administration (GSA) and U.S. Department of Energy (DOE) Building Commissioning Guide, July 30, 1998.
NFPA defines commissioning as a qualitative and quantitative process used to accomplish the following:
The GSA/DOE definition is simpler: “a process for achieving, verifying and documenting that the performance of a building and its systems meet the design intent and the owner and occupant needs.”
Both definitions highlight the two important aspects of commissioning—verifying the system is working correctly as built and providing a baseline to check if it is still working correctly in the future. The GSA document states that electrical systems commissioning adds approximately 1 to 1.5 percent of system cost with these costs being recouped many times over in deferred or avoided future costs.
But what about commissioning with regard to the power quality characteristics of the facility, its electrical infrastructure, the electrical loads and the electrical supply? Just like the GSA/DOE definition being concerned with the performance relative to the owner/occupant needs, power quality is concerned with the quality or performance of the electrical supply with regard to the needs of the electrical loads that use it. The overall process is similar to those found in the aforementioned documents but with a slightly different focus.
First, the initial tests should be done without any of the facility’s systems energized so that the baseline voltage characteristics, including steady-state magnitude, frequency and distortion, can be measured without influence from the facility’s loads. This test should be performed for a week or longer, so other typical power quality phenomena, such as sags, swells and transients, may also be assessed. Of course, the test doesn’t provide a true benchmark, as there are seasonal effects that it wouldn’t capture, but it is a start.
For example, there may be a power factor correction capacitor bank that switches on every morning at 6 a.m., causing a transient to be a problem for the facility once operational. Ideally, this test would be run before even the first shovel of dirt is overturned, but that isn’t often practical without electric utility support.
As individual facility loads are energized, the monitoring should continue with the addition of the current characteristics (inrush or peak values, steady-state magnitude and distortion) to the data collected, as well as power-related parameters of volt-amperes, watts, volt-amperes reactive and power factor. Notes of what was turned on and when can draw correlations to the effect and characteristics of the various loads.
Ideally, multiple power quality monitors should be used at the point of common coupling, the distribution panel of the loads being energized, and the point of utilization (the load). It is invaluable data for the future when a problem arises or when new equipment is added or replaced.
A common complaint is “we had no problems with the old equipment.” Was the old equipment not susceptible to power quality phenomena, or has the quality of the supply changed? Suppose turning on one large load produces a 5 percent reduction in voltage for a couple of seconds. What will happen to other equipment if several of those loads are energized at the same time?
Where either the utility or facility provide redundant power sources (such as with uninterruptible power supplies), each of the operational combinations also must be verified. In most operations, it is risky to assume the backup generator is powering only the loads it is supposed to run and can run off it properly, especially with critical operation power systems, as defined by NFPA in the National Electrical Code.
The test plan and the results should be stored in a reliable and retrievable location, so future test data can be included as the facility and equipment evolves and ages. NFPA 70B provides a good selection of forms in the annex that can help decide what should be recorded.
The Electric Power Research Institute states that U.S. businesses lose $119 billion in revenue per year from power quality-related issues. So, it would seem wise for a power quality commissioning process to verify that the electrical supply, infrastructure and loads are all power quality-ready now and in the future. Your customers would be paying a little now or a lot more later.
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.