Lurking in the shadows of even the most unsuspecting operations — from corporate to commercial to industrial facilities — is a condition known as poor voltage quality, a hidden expense that typically goes undetected and undiagnosed until costly failures occur. Voltage events interrupt sensitive processes, shorten the useful life of equipment, and cause computer and communications problems. Oftentimes, these disturbances trigger needless expenses in the form of implemented solutions to misdiagnosed problems. Unless the source of the problem is correctly identified and its cause found and repaired, the costs and time required to solve the problem add up quickly.
Defined in terms of magnitude (amplitude) and duration (length), voltage events — appearing in the form of sags, swells, impulses, and total harmonic distortion — can affect equipment performance in different ways. Typically, the ultimate impact of such events is determined by the sensitivity of the equipment on the branch circuit.
A sag is a period of low voltage. Minor sags occur frequently, sometimes without disturbing equipment performance. Major sags, on the other hand, always disturb equipment performance. Sags occur for many reasons, including voltage drop caused by long runs of wire, switching loads, poor wiring, and overloaded branch circuits.
A swell is a period of high voltage. Swells have serious impact on equipment function; however, they are not as common as sags. Both minor and major swells affect equipment performance.
An impulse is a short burst of energy that lasts for less than a cycle. Impulses range in magnitude from twice the nominal voltage to several thousand volts. Not every impulse has an impact on equipment performance. However, when impulses occur repeatedly over time (or when the energy level is very high), an impulse can cause equipment degradation or even immediate failure.
AC voltage is a sine wave that repeats 60 times per second (Hertz = cycles/second). This is the fundamental frequency. Harmonics are alternate frequencies that distort the sinusoidal waveform. Total harmonic distortion (THD) is measured as a percentage of the fundamental frequency. Equipment runs well on voltage that is a clean (or slightly distorted) sine wave. High levels of distortion may cause equipment problems. On single-phase branch circuits, levels of THD greater than 5% to 8% should be investigated.
In many cases, upon further investigation by a power quality professional, problems that have existed for years are traced back to undetected voltage events caused by the culprits outlined above. After voltage interruptions make their presence known, the first question end-users typically want answered is, “How did they get started in the first place?”
