Modern electrical installations supply power to a wide variety of non-linear loads, where the current drawn does not have a linear relationship with the voltage supplied. In other words, even if the supply voltage signal is a perfect sinewave when measured with an oscilloscope, the resulting current may have a distorted waveform. The following are some types of electrical equipment that produce non-linear currents:

  • Electrical motors and transformers: They behave linearly with low voltage and current, but display a non-linear response once their cores operate near saturation.
  • Electronic equipment: This includes equipment such as computers, instrumentation, actuators and variable frequency drives (VFDs).
  • Lighting fixtures that operate with ballasts or drivers: Fluorescent, HID and LED lamps, to mention a few examples.

The degree of distortion in voltage and current waveforms tends to increase according to the number of non-linear loads in a facility. However, there is a method called Fourier analysis that allows these distorted voltage and current signals to be decomposed into:

  • A fundamental 60-Hz signal: The pure sinewave that would be present without distortion.
  • A series of signals with frequencies that are odd multiples of 60 Hz, which are called harmonics.
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