Harmonics (electrical power)
Sinusoidal wave whose frequency is an integer multiple
In an electric power system, a harmonic of a voltage or current waveform is a sinusoidal wave whose frequency is an integer multiple of the fundamental frequency. Harmonic frequencies are produced by the action of non-linear loads such as rectifiers, discharge lighting, or saturated electric machines. They are a frequent cause of power quality problems and can result in increased equipment and conductor heating, misfiring in variable speed drives, and torque pulsations in motors and generators.
Many non-linear electrical loads draw current only during portions of each AC cycle, producing a periodic but non-sinusoidal current waveform. If the waveform is periodic, it can be represented by a Fourier series as the sum of the fundamental frequency and harmonic components at integer multiples of the fundamental frequency.
Harmonics are usually classified by two different criteria: the type of signal (voltage or current), and the order of the harmonic (even, odd, triplen, or non-triplen odd); in a three-phase system, they can be further classified according to their phase sequence (positive, negative, zero).
The measurement of the level of harmonics is covered by the IEC 61000-4-7 standard.
Current harmonics
In a normal alternating current power system, the current varies sinusoidally at a specific frequency, usually 50 or 60 hertz. When a linear time-invariant electrical load is connected to the system, it draws a sinusoidal current at the same frequency as the voltage, although not always in phase with the voltage).
Current harmonics are caused by non-linear loads.
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