It wasn’t long ago when flashing digital clocks were the most likely power-quality-related effect of an interruption. Today more than 70 percent of homes have computers, and nearly that many have Internet access. That, coupled with an ever-increasing amount of electronics in household appliances, means an acceptable quality of electrical supply is needed more than ever to keep homes and workplaces running smoothly. With more people telecommuting for work, if the household electric service is not adequate for the equipment it powers, productivity will be affected just like in the office or factory.
Just as average homeowners aren’t very knowledgeable about what makes up their electric bill and how their usage affects it, the effect of the electrical quality on the operation (or misoperation) of appliances and equipment in their house is even more of a mystery. And unfortunately, there is a large amount of misinformation out there on the Internet. For example, one person’s solution to sags was to add capacitor banks. While capacitors store energy for direct current (DC) circuits, their use on alternating current (AC) systems is primarily for power factor correction or as a part of a filter for harmonics. They cannot provide any real protection from voltage sags on AC systems.
I found another claim that a “poor” power factor of 0.92 (which actually is fairly good) actually “magnifies a sag” to make it worse. Power factor is the ratio of real power (in watts) divided by the apparent power (in volt-amperes). A sag is a decrease in the voltage, which will proportionally change the watts and the volt-amperes, leaving the power factor as it was. So, what can be done?
Homeowners can do many things in conjunction with licensed electricians to improve the “productivity” in their homes and reduce the susceptibility to power quality phenomena. Most of their options are similar to steps that would be taken at a commercial or industrial facility:
• If lights on one circuit are blinking or flickering and not on others, look for a large load on that circuit that starts up periodically, such as a microwave, air conditioner or tankless electric hot water heater. Adding separate circuits for such large loads that cause voltage sags or fluctuations (and for susceptible equipment) can eliminate the problem.
• If necessary, install retrofit “soft-start kits” on motors of heating, ventilating, and air conditioning (HVAC) units to minimize effect from startup.
• Install a properly rated transient voltage suppressor at the service entrance for the electrical supply and the telecom wiring, and ensure the grounding conductor has a low impedance-path-to-earth ground. The devices should be listed for UL 1449 second edition and UL 497a for electrical and telecom, respectively.
• Verify that the wiring and grounding is performed according to the National Electrical Code (NEC) throughout the home, including the grounding electrodes and connections to the utility service. A “bad neutral” connection can cause serious damage to equipment. Likewise, improper distribution of the current loading on one of the 120-volt buses can lead to voltage unbalance.
• If the occurrence of severe sags that cause lock-ups or resets warrants it, use small uninterruptible power supplies (UPS) for PCs, routers, printers, etc. A laptop is generally immune to sags as it runs off its internal battery, with the AC used to charge it (like a mini-UPS).
• The increased use of nonlinear loads, such as information technology equipment, TVs, newer HVAC systems, and compact fluorescent lamps, can create significant harmonic currents that can lead to “flat topping” of the voltage waveforms as well as overheating of motors and transformers.
• Long-term interruptions (outages) fall under the realm of what is called “reliability” rather than “power quality.” For those types of events, a backup generator is probably the best solution. However, the average homeowner probably isn’t aware of the safety precautions that are needed when using a backup. For example, if the generator is not properly grounded, equipment in the house running off it may be “floating” with respect to ground or weakly grounded through interconnections to other equipment that is still plugged into wall outlets. A properly installed break-before-make transfer switch with the proper wiring and circuit protection, according to the NEC, should be installed by a licensed electrician, not the homeowner.
According to the J.D. Power and Associates 2011 Electric Utility Residential Customer Satisfaction Study, residential electric utility customers are less satisfied with power quality and reliability than in 2010. It sounds like it’s time for the electrical contractor “doctor” to start making more house calls.
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.