Power quality issues arise from a number of sources, both internal and external, and the factors are never quite the same from day to day.
"Power fluctuation is caused by various pieces of equipment going on and off, bringing spikes into the supply," notes Subodh A. Kumar, an IFMA fellow and president of Chartered Facility Management Group Inc., Pasadena, CA. "The same situation can occur from others within the building or even the region, as well as from the quality of the supply grid and its capacity."
External sources include transient voltages, such as lightning strikes, and voltage and/or frequency sags or surges from the electrical power company source. Internal sources of poor power quality often include momentary in-rushes from larger equipment causing voltage and frequency dips in the electrical distribution system integral to a facility. Culprits include large motor loads, large distribution transformers, and, in the case of healthcare facilities, radiology equipment start-up.
That's not to say smaller, more mundane electronics don't have an impact on a building's electrical load.
Greg Massey, PE, an electrical engineer based in Kansas City, says while an
electrical load profile is in constant transition, it does go through a predictable
cycle each day.
"Loads build in the morning as the doors open for business and employees
turn on computers, lights, radios, fans, coffee pots, displays, microwave ovens,
and other machinery," Massey says. "Loads begin to taper off in the
evening as employees leave work or when there is a shift change. Typically,
minimal lighting and environmental loads exist overnight or whenever the business
closes for the day."
Likewise, these loads also exhibit a seasonal cycle. Depending on the part of the country and the type of heating and air-conditioning used, the electrical loads will be higher depending on the weather, peaking either in the summer or in the winter. Because of this cyclical nature, it takes time to determine the root cause of intermittent power quality problems. Typically, an existing electrical system must be evaluated over time.
"An owner or facilities manager can spend valuable time pursuing a quick fix when the system should be evaluated over time," Massey says. "Many times, the approach to poor power quality is to treat symptoms while neglecting to look for the cause of the problem. It's analogous to taking two aspirin and calling the doctor in the morning."
In most cases, Massey says, the quick fix might appear to solve the problem, but because many symptoms of poor power quality take a long time to appear, the fast solution simply buys time by marginally improving the operating conditions of selected equipment.
"In other words, it takes longer for equipment to fail," Massey says.
Treating symptoms with a Band-Aid approach also can result in solving the wrong problem with overly expensive equipment replacements that aren't really necessary.
For example, many power quality problems are manifested in transformers that overheat.
Transformers can overheat as a result of such power quality-related issues as overvoltage, current harmonics, voltage harmonics, and resonance, Massey says. Transformers also can overheat from insufficient ventilation, high ambient temperature, overloading, and single phasing. Whether a problem is related to the transformer itself or simply symptoms of a power quality issue is something that needs to be determined over time.
"Replacing a failed general purpose dry-type transformer with a K-rated transformer capable of supplying harmonic-generating loads is a very expensive solution if all that is required is routine maintenance to clean transformer vents," Massey says.
Power quality experts also caution facilities professionals of the importance of realizing that their power equipment offers no more protection than the weakest link in their system.
Electrical experts at GRG Vanderweil Engineers Inc., Maitland, FL, recently assisted a client with an uninterruptible power source (UPS) for an existing data center power supply. The client had been experiencing downtime for a non-related issue, and Vanderweil engineers recommended use of a battery monitoring system to ensure uninterruptible power availability.
Upon completing the installation of this system, the facility discovered two batteries had failed within its UPS system.
"The failure of any additional batteries could have affected the ability of the UPS to supply uninterruptible power," notes Vanderweil engineer Neal Boothe. "This client would not have learned of this failure until the moment of a power outage when UPS power was expected but unavailable."
A proper electrical distribution system is made of components that are carefully selected and balanced to function as a system. Any modifications to such a system must be made with diligent care. And, consideration must be given to any effects resulting from system changes.
"It's important to fully understand and correct the true causes of poor
power quality, using symptoms as clues," Massey says. "Expanding the
medical analogy, we can treat symptoms with quick fixes all day, but there will
be side effects from drug interactions and the pharmacy bill is going to be
expensive."
