New technology introduces new challenges Harmonics are the by-products of modern electronics. They are especially prevalent wherever there are large numbers of personal computers, adjustable speed drives and other types of equipment that draw current in short pulses.
This equipment is designed to draw current only during a controlled portion of the incoming voltage waveform. While this dramatically
improves efficiency, it causes harmonics in the load current. And that causes overheated transformers and neutrals, and tripped circuit breakers. If you were to listen to an ordinary 60 cycle power line, you’d hear a monotone hum. When harmonics are present, you hear a
different tune, rich with high notes. The problem is even more evident when you look at the wave form. A normal 60 cycle power line voltage appears on the oscilloscope as a near sine wave When harmonics are present, the waveform is distorted These waves are described as non-sinusoidal. The voltage and current waveforms are no longer simply related—hence the term “non-linear.”
A mystery is occurring in today’s office buildings and manufacturing plants. Transformers supplying seemingly average loads are overheating. Neutral conductors in balanced circuits are overheating from excessive loads. Circuit breakers are tripping for no apparent
reason. Yet the standard troubleshooting procedures show everything to be normal. So what’s the problem?
In one word—harmonics.
Harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency. For
example if the fundamental frequency is 60 Hz, then the second harmonic is 120 Hz, the third is 180 Hz, etc. Harmonics are created by
non-linear loads that draw current in abrupt pulses rather than in a smooth sinusoidal manner. These pulses cause distorted current wave shapes which in turn cause harmonic currents to flow back into other parts of the power system.