Power quality has finally made the big time in the United States, getting mentioned at the federal level under the Energy Independence and Security Act of 2007. One of the smart grid functions is stated as “the ability to measure or monitor electricity use as a function of time of day, power quality characteristics such as voltage level, current, cycles per second, or source or type of generation and to store, synthesize or report that information by digital means.” It may seem small in a hundred-page document, but it’s a start, especially with all that’s said about the smart grid.
Many of the other parts of the world have voltage-quality compliance written into their laws, both for the producers of electricity that are required to deliver a certain level, and for the equipment powered from such that isn’t allowed to “corrupt” the voltage quality beyond a certain level. So what should those acceptable levels be for here in the United States?
Before we ask that question, though, we should ask what’s established currently. There have been three large-scale power quality surveys in North America in the past 30 years. The first one was conducted by National Power Laboratories (NPL) in the ’80s and was measuring the power quality characteristics at the point-of-utilization, also known as the receptacles where loads plug in. At that time, power quality monitors were primarily textual-based indicators of changes in both the root mean square (rms) and transient voltage and current. Loads back then were still primarily inductive from electric motors, though harmonics were present from fluorescent lights and some adjustable speed drives.
In the 1990s, we saw the Electric Power Research Institute (EPRI) Distribution Power Quality (DPQ) program get underway to benchmark the power quality at the distribution level. Three hundred monitors were placed at the substations, at the mid-point on feeders and at the end of the feeders. This was to see how increased nonlinear loads, such as computers, were affecting the harmonics as well as the rms variations, transients and frequency stability. Waveform data allowed additional post-processing analysis. Rapid voltage changes and flicker weren’t part of that study but are common reporting elements in the voltage compliance standards of other countries.
The Canadian Electric Association survey split the distance between the two and monitored at the point of common coupling (PCC), also known as the service entrance. At the PCC, harmonic spectrums look different than at the point of use (POU) as the higher order harmonics often cancel out when the different circuits within the building are summed together at the PCC. Sags at the PCC may not be as severe as directly at a large horsepower motor, just as a load-induced sag would have even less effect on the distribution system. Generally, the farther away from the source of power, the more the effect.
So, what does the past have to do with the present? All of these surveys are more than a decade old. The load profile of the typical commercial and industrial facility has changed. The amount of electricity being consumed has increased dramatically, and estimates show no slowdown in sight. New types of electrical generation, from solar to wind to fuel cells, are putting distributed generation from less “stiff” sources into the grid than the traditional large utility nuclear/hydro/fossil fuel generators. Cost-cutting measures at some electric utilities have affected maintenance programs on equipment and power lines. Electric vehicles are starting to gain momentum in the market place, which will place additional demands on a somewhat strained and constrained electric grid.
So before we make it “smarter” and maybe even pass laws about what goes into and what can go on it, wouldn’t it be nice to know what the present state of things are at all three points—the POU, PCC and distribution system? How have things changed since those surveys? Where do we really need to focus our attention and improve things? Though, there are discussions on a new EPRI DPQ project, it seems we need some answers now and not just on the utility system if and when that study takes place.
So, I am proposing that all of you who are actively engaged in power quality monitoring could help. To play on John F. Kennedy’s famous inauguration speech, ask not what power quality can do for you; ask what you can do for power quality.
E-mail trend or time plot data files of power quality measurements in Excel format to email@example.com, along with a brief description of the site being monitored (where, when, how, what kind of service and loads, etc.). We will compile the data as received and report back periodically in the column as to what the state of the grid is before it gets smarter, so that we can tell later if it really improved. Maybe even those that will eventually try to pass laws will be interested in the facts.
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680