For most people who have limited experience performing power quality troubleshooting or benchmarking audit surveys with a power quality analyzer, understanding what to do first can be a bit daunting. Asking where to begin is a frequent call to tech support. To quote Lewis Carroll from “Alice’s Adventures in Wonderland,” “’Begin at the beginning,’ the King said, gravely, ’and go on till you come to the end: then stop.’” The key here is identifying what is the beginning and, eventually, what is the end.
Start with safety
Safety should always be the beginning, and that starts with determining if one is qualified to safely carry out the required tasks. To paraphrase NFPA 70E and OSHA, a qualified person is one who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training to identify and avoid the hazards involved. This may seem like a Catch-22, as how can one be qualified without knowing where to begin. It’s sort of like the job ads that state “experienced persons only need apply.”
Since most of you readers are licensed electricians, the training to achieve that level of certification should cover most of the requirements for being a qualified person with regards to the installed equipment, safety training and hazards. For those without that qualification, don’t do it. Electricity is not a self-taught, on-the-job training adventure. Hire a qualified electrician to make your connections safely.
That leaves primarily the instrument. How and where should it be safely and properly connected to get the desired results? An instrument with UL or equivalent regulatory listing is a must, as it has passed the tests required to safely and reliably connect to the circuits, provided that the limits of the instrument are observed.
PQ instruments
Most PQ instruments’ voltage connections are rated for 600V AC or 720V AC. Current measurements for portable instruments are usually done with current probes, the ratings of which also must be observed for current and voltage. Read the specs, particularly with regards to the crest factor or peak current and the minimal current level. In many applications, there will be a very short-duration overcurrent condition that has important information in the waveforms. On a 30A RMS circuit, there can be peak current values upwards of 130A lasting several cycles that may not trip the breaker but give clues as to what caused the problem.
Always wear the properly rated PPE for the arc flash hazard where the measurements are made. A minute “saved” may cause a lifetime of pain or even cost a life. All injuries resulting in lawsuits that I dealt with during my tenure with an instrument manufacturer were preventable. Whenever possible, de-energize the system before making connections—and most instrument manufacturers state this in their instructions. Live connections are part of business but must be done according to the requirements in NFPA 70E, OSHA 1910 Subpart S and OSHA 1926 Subpart K.
No matter how boring, read the user’s guide. Know what type of circuit to monitor and how the instrument’s voltage and current probes should be attached to the conductors. While vendor software can claim to make post-collection corrections for improper connections, individual sampled data points that make up the waveforms and power numbers will likely remain corrupt. Some instruments have easy-start or auto-connect features that can determine the circuit and provide feedback if connected properly. Do a sanity check on the voltage, current, power, power factor, V-I phase angles and other key parameters before starting to monitor.
Where to begin making the connections is usually application-dependent. If the problem is with an individual piece of equipment or the task is to determine the health and efficiency of a particular load, then the connection point must be as close to the power input as the load. That isn’t always practical where the conductors may not be exposed as separate wires for the current probes to clamp on to. In some single-phase applications, measuring the line-to-neutral and neutral-to-ground voltage can determine the current.
When the problem is with the entire circuit, the breaker or distribution panel is the place to connect, but do not leave the panel cover off after making the circuit connections. The site must be rendered safe, because monitoring can last weeks or months. The same applies when making a benchmark audit survey for an entire facility or when trying to determine if the problem originates upstream at the point of common coupling from the power source (the electric utility) or downstream from loads in the facility.
Small PQ monitors can be placed inside the cabinets and communicate through wireless media to the network software from the instrument vendor. If possible, providing simultaneous monitoring points can decrease the troubleshooting time and give a broader view of the electrical infrastructure’s performance.
Next month’s article will continue exploring the PQ monitoring process “down the rabbit hole” until the desired end is reached—until we stop, per the King.
stock.adobe.com / Andrey Kokidko
About The Author
BINGHAM, a contributing editor for power quality, can be reached at 908.499.5321.