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Total Harmonic Distortion (THD) is a measure used to quantify the level of distortion present in an electrical signal, typically a waveform such as an alternating current (AC) voltage or current. Here’s a detailed explanation of THD:

Total Harmonic Distortion (THD) is defined as the ratio of the root-mean-square (RMS) value of the sum of the squared individual harmonic amplitudes to the RMS value of the fundamental frequency component of a complete waveform.

Key Concepts:

  1. Harmonic Components: In an AC waveform, the fundamental frequency represents the primary sinusoidal waveform, while harmonic frequencies are integer multiples of the fundamental frequency. Harmonic components can result from various sources, including non-linear loads, power electronic devices, or imperfections in electrical systems.
  2. RMS Values: The RMS value of a waveform represents the effective value of the waveform’s voltage or current, taking into account both its magnitude and its waveform shape. It is calculated as the square root of the average of the squares of the instantaneous values over one cycle of the waveform.

To calculate Total Harmonic Distortion (THD), follow these steps:

  1. Determine the RMS value of the fundamental frequency component of the waveform.
  2. Calculate the RMS value of each individual harmonic component present in the waveform.
  3. Square the RMS value of each harmonic component and sum these squared values.
  4. Divide the sum of squared harmonic amplitudes by the RMS value of the fundamental frequency component.
  5. Multiply the result by 100 to express THD as a percentage.

The formula for calculating Total Harmonic Distortion (THD) is:


Total Harmonic Distortion (THD) is expressed as a percentage and indicates the extent to which harmonics contribute to the overall distortion of the waveform. Lower THD values indicate less distortion and higher waveform fidelity, while higher THD values signify greater distortion and potential performance issues in electrical systems.

THD is commonly used in electrical engineering, power systems, audio engineering, and electronics to assess the quality and integrity of electrical signals, particularly in AC power distribution, audio amplification, and electronic instrumentation.

In summary, Total Harmonic Distortion (THD) quantifies the level of distortion present in an electrical waveform by comparing the magnitudes of harmonic components to that of the fundamental frequency component. It provides valuable insight into waveform quality and is essential for assessing the performance and efficiency of electrical systems and devices.

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