HARMONICS- Understanding the Facts

Understanding what is important to know about harmonics can be challenging for those without extensive electrical engineering backgrounds. In this two part series of articles, the first article will help to clarify what those important facts are, and the second will help tell when to raise the flag. What is a Harmonic The typical definition for a harmonic is “a sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency.” [1]. Some references refer to “clean ” or “pure ” power as those without any harmonics. But such clean waveforms typically only exist in a laboratory. Harmonics have been around for a long time and will continue to do so. In fact, musicians have been aware of such since the invention of the first string or woodwind instrument. Harmonics (called “overtones ” in music) are responsible for what makes a trumpet sound like a trumpet, and a clarinet like a clarinet. Electrical generators try to produce electric power where the voltage waveform has only one frequency associated with it, the fundamental frequency. In the North America, this frequency is 60 Hz, or cycles per second. In European countries and other parts of the world, this frequency is usually 50 Hz. Aircraft often uses 400 Hz as the fundamental frequency. At 60 Hz, this means that sixty times a second, the voltage waveform increases to a maximum positive value, then decreases to zero, further decreasing to a maximum negative value, and then back to zero. The rate at which these changes occurs is the trigometric function called a sine wave, as shown in figure 1. This function occurs in many natural phenomena, such as the speed of a pendulum as it swings back and forth, or the way a string on a voilin vibrates when plucked. Figure 1. Sine Wave The frequency of the harmonics are different, depending on the fundamental frequency. For example, the 2nd harmonic on-1.