For the most part, the medical doctor who makes house calls is a thing of the past. But the image of the black leather bag that the doctor carried along to provide relief (or deliver a baby) has been captured in the minds of even those who only have seen it in the movies or a Norman Rockwell painting. Many items carried in the typical doctor’s bag parallel the items in the power quality tool bag; both sets of tools are intended to cure the ills of their respective patients or power systems. Here’s but a few.
• Masks/gloves and faceshields/gloves
Before starting any power quality investigation, the first rule is to protect the “doctor” from becoming endangered by the patient. Following the safety guidelines set out in NFPA 70E and wearing the proper personal protective equipment for the job and arc flash hazards are equally essential.
• Thermometer and infrared scanner
Both take the patient’s temperature to help determine their health. The infrared scanner can identify loose connections and overheated equipment or components within equipment without having to make contact with live circuits.
• Stethoscope and oscilloscope
Being able to “hear” heart beats can determine irregularities. Power quality monitors with graphic displays can show distortion in waveforms indicative of harmonics as well as unbalanced conditions, phase shifts and even the modulation of waveforms that results in light flicker.
• Sphygmometer and current probe
Whether measuring blood pressure or the pressure of the electron flow, these devices can let their users know if things are getting too close to the point of safety for the “pipes” that carry the flow. Today’s bag should include both clamp-on and flexible CTs of the proper ratings for the maximum current flow anticipated. Some applications today may require specialized probes, such as Hall effect types that can also measure DC current.
• Notebook and notebook (computer)
Having a permanent record of treatments is as important as is writing down the history and layout of the facility, what symptoms that the occupants of the facility noted, and what were the measurements for future reference. Just like the baseline blood test and EKG results are important for a doctor to determine what has changed with the patient, so are the steady state values of voltage, current, frequency, distortion, and power and power factor values, along with the power quality phenomena captured, such as rate of occurrence and magnitude of sags, swells, transients and other short-duration events.
• Sutures and needles and screwdrivers and wrenches
Sewing up lacerations is part of the three B’s of first aid (breathing, bleeding, breaks). Having a screwdriver and a wrench to open panels and tighten loose connections safely (see above) is a common first aid for electrical connections, whether the loosening occurred from vibration or thermal heating of changing harmonic currents.
• Remedies and mitigation equipment
After all of the examination, tests and first aid are applied, some visits require a more in-depth treatment or mitigation to heal the system. Whereas the doctors may have been able to carry such in their bags, your problem may require things much larger than what could fit in a bag to mitigate a power quality problem. Sometimes additional circuits must be run to separate the source of the problem from equipment it is affecting, such as high harmonic currents from large adjustable speed drives or a separate utility feed to an automatic transfer switch. Maybe a harmonic filter, transient voltage surge suppressors, improved grounding system, or a uninterruptible power supply is needed. But be sure to know what is wrong before applying the solution. Giving the wrong medicine to a patient can make the situation worse.
• Aspirin and aspirin
Some problems can be a real pain to solve. A problem may not repeat itself for months, measurements may show nothing apparent, or maybe you just can’t get to the circuits that you need to measure. Sometimes it is best to take some relief, step back, talk over the results with someone else, and try a fresh approach the next day. Remember that the data should support expected results from Ohm’s and Kirchoff’s Laws. If your results are inconsistent with these infallible laws, it’s time to ask for a second opinion, and change measuring equipment and techniques.
The power quality doctor rarely if ever, has an opportunity where the patient comes to them. It is often under stressful conditions (a facility is down and is losing $20,000 per hour) that the house call must be made. Knowing what your tools can and cannot do before you get to the scene is key to helping a quick recovery. And don’t forget, ongoing education to stay current with the latest techniques and tools available is just as important as for the medical doctor.
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.