PQ safety is often overlooked, despite the danger
Part of any power quality seminar material should cover the aspects of safety, especially for anyone who must connect/disconnect the voltage and current probes for power quality monitors. An excellent document to refer to is the NFPA 70E Standard for Electrical Safety in the Workplace, 2004 edition. It covers protection to the employee from electrical hazards such as shock, arc blasts and explosions initiated by electricity. There is a wealth of information in that document, ranging from the proper personal protective equipment (PPE) to be worn based on an evaluation of the hazard of the work environment to energized electrical work permit requirements to ensure people performing this type of work are properly trained and equipped.
One should start with the definition of a “Qualified Person,” which OSHA’s 29 CFR 1910, “Occupational Safety and Health Standards,” the National Electric Code, NFPA 70E and other documents refer to as one who is familiar with the construction and operation of the equipment and the hazards involved. They should also know how to avoid those hazards. Beside all of the efforts to raise the awareness on such topics as arc flash, many people still seem to disregard the requirements that would seem like common sense. It doesn’t just happen to someone else. Nearly one person dies each day from electrical accidents, and five to 10 people are seriously burned from an arc flash explosion. Like most accidents, many of these are preventable, and the extent of the injuries could be greatly reduced by following the precautions.
In power quality measurements, there is the same hazard. Yes, it is rare to connect a power quality monitor to medium- or high-voltage systems, but the connections made to the low-voltage systems are often in proximity to such. Even the low-voltage systems (under 1kV) can cause fatal or serious injuries. The explosions can cause instantaneous third-degree burns, broken bones from the shock wave and/or result of being hurtled back through the air, deafness from the sound, and permanent loss of functionality of various parts of the body.
There are some tools useful for power quality monitoring and electrical equipment maintenance in general that don’t require contact to be made with energized circuits. One of the more popular of these tools is the infrared scanner, which can be found in the $100 to $1,000 price range. Like any tool, the user should be properly trained and familiar with the operation and limitations of such devices. Even the less expensive units often feature a laser sighting capabilities that help pinpoint where the temperature measurement is being made with an accuracy of +/-1 percent.
Harmonics is a power quality phenomenon that can result in an increase in heat. The heat can be the result of additional losses in electromechanical equipment, such as motors and transformers. Harmonic losses increase as the frequency of the harmonics increase, often by the square of the harmonic number. Some of the harmonic frequencies, called the negative sequencing components, impose a reverse rotation effect on rotating equipment—trying to turn in the opposite direction. This also results in additional heat.
Additional harmonic currents can also increase the heating in wiring and connection points. With many commercial and industrial facilities, the harmonic currents are larger during the daytime, when personal computers and other information technology equipment are running. At night, many people turn off these harmonic-producing loads. In a factory that doesn’t run three shifts, the harmonic-producing loads of adjustable speed drives will also be turned off or reduced during the off hours. The result is a heating and cooling cycle that works to loosen mechanical connections of conductors. As the connection loosens up over time, the losses in that connection increase, as does the heat that is detectable by an IR scanner by scanning for such hot spots.
Infrared scanning is not a panacea, nor a replacement for visual inspection. Like any tool, it has its limitations, including the skill level of the operator. It requires line-of-sight to get an accurate reading, and the readings can be influenced by external factors, such as the weather, when making outside measurements. Be sure to fully understand the manufacturer’s operating instructions. Chapter 20.17 of the NFPA 70B Recommended Practice for Electrical Equipment Maintenance provides a good overview on use of such equipment.
There are many tools available to help solve PQ problems. At a recent PQ seminar, the emphasis was made on using all of your senses, except the sense of touch (though someone in the audience pointed out that “taste” is also not recommended). Inadvertent contact with energized conductors has resulted in far too many injuries and deaths, especially when the person has not taken the extra minute to put on the proper personal protective equipment. It doesn’t just happen to someone else. Don’t become a statistic. EC
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.