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Harmonic Problems in Power Transformers

By Phill Feltham

Preventing malfunction in power transformers


Harmonics are another power quality phenomenon that can cause equipment to malfunction. Harmonics are a sinusoidal component of periodic waves that have frequencies that are multiples of the fundamental frequency. Harmonics can cause computer equipment to lock up or cause the data to become garbled as well as causing transformers, motors, and neutral lines to overheat.

Linear loads such as incandescent lights draw current equally throughout the waveform. Non-linear loads such as switching power supplies draw current only at the peaks of the wave. These non-linear loads cause harmonics. If the fundamental frequency is 60 hertz (Hz), then the second harmonic would double this number to 120Hz, the third harmonic would be three times (180Hz), and so on. Typically, current harmonics will not propagate through a system. Voltage harmonics will propagate through a system, as they can pass through transformers. As non-linear currents increase, they can cause harmonics in the voltage.

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