What is Total Harmonic Distortion (THD) in Power Systems?
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Total Harmonic Distortion (THD) is a critical parameter in power systems, indicating the presence and impact of harmonics in electrical networks. Harmonics are sinusoidal voltages or currents at frequencies that are integer multiples of the fundamental frequency, typically 50 Hz or 60 Hz. These harmonics arise due to the non-linear characteristics of loads and power electronic devices, leading to various adverse effects on power quality and system performance. Definition and Calculation THD is defined as the ratio of the root mean square (RMS) value of all harmonic components to the RMS value of the fundamental frequency. It is a dimensionless quantity usually expressed as a percentage. Mathematically, THD for voltage is given by: THD = V 2 2 + V 3 2 + V 4 2 + ⋯ + V n 2 V 1 × 100 % \text{THD} = \frac{\sqrt{V_2^2 + V_3^2 + V_4^2 + \cdots + V_n^2}}{V_1} \times 100\% Where: V 1 V_1 V 1 is the RMS voltage of the fundamental frequency. V 2 , V 3 , … , V n V_2, V_3, \ldots, V_n V 2 ,