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Modern Equipment Can Create Harmonic Distortion
"Harmonics" are a growing power quality problem that can cause malfunctioning of desktop computers and other microprocessor-based equipment. Other common problems include overheating in motors and wires, deterioration or failure of power factor correction capacitors, erratic operation of breakers and relays, and pronounced magnetic fields near transformers and switchgear.

EWEB engineer Alan Fraser (right) helps a customer investigate a possible harmonics problem.

In recent years, the number of these non-linear loads has increased dramatically. Just think about all those new computers and other microprocessor-based devices--from cash registers to copiers. Ironically, some of the equipment--such as microprocessors that are most sensitive to harmonics--also create harmonics.

To make matters worse, harmonics generated inside one building can sometimes travel back through utility lines to other buildings, especially if the buildings share a common transformer.

There are many solutions available to deal with harmonic problems. Some simply treat the symptoms by making systems more tolerant of the harmonic levels. Others eliminate or reduce harmonics by filtering or canceling them out. All solutions to harmonic problems require careful analysis before any mitigation strategies are employed.

The best solution depends on a large number of factors. It's vitally important to identify the sources and employ a solution that doesn't create new problems. EWEB can provide more information about harmonics in your business. Assistance is available by calling our Power Quality Hotline at 345-8984.

For most people, the word "harmonics" brings to mind something musical. If you could look at a plucked guitar string in slow motion, you would see it vibrates in several ways. First, it vibrates end to end, anchored at the head of the guitar and the bridge. This is called the fundamental. The string also vibrates as if anchored at the bridge and in the middle of the string. This vibration on top of the fundamental vibration is called the second harmonic. The frequency of the second harmonic is two times the fundamental. The frequency of the third harmonic is three times the fundamental, etc. Harmonics are superimposed on the fundamental to produce the sound we hear.

The translation to electricity is almost direct. Electricity is produced and delivered in its fundamental form as a 60 cycles per second (Hertz) sine wave. Once inside your business, certain types of equipment can superimpose harmonics on the basic sine wave. Harmonics are multiples of the 60 Hertz wave. For example, the second harmonic is at 120 Hertz, the third is at 180 Hertz, etc.

Because harmonics are superimposed on the fundamental waveform, the frequency of the electricity no longer follows a smooth sine wave. Most electrical equipment expects to see a smooth frequency and distortions created by harmonics can cause a variety of problems.