Harmonics

Introduction

Harmonics are higher-frequency waveforms that are superimposed on the fundamental frequency of a circuit. The fundamental frequency is the normal operating frequency of the system (typically 50 Hz or 60 Hz). When harmonics are present in sufficient magnitude, they distort the shape of the original sinusoidal waveform.

The amount of distortion applied to the fundamental wave depends on the type, magnitude, and order of the harmonics present. As harmonic content increases, the waveform becomes more complex and less sinusoidal.

Origin of Harmonics

Harmonics have become more prominent over the last few decades due to the widespread use of non-linear electrical loads. These include electronic motor drives used in fans, pumps, and compressors; power supply switching circuits such as rectifiers, power converters, and thyristor-based controllers; phase-controlled electronic loads; and high-frequency energy-saving fluorescent lamps.

These devices draw current in a non-sinusoidal manner, meaning the current waveform does not faithfully follow the shape of the supply voltage waveform. As a result, harmonic currents are generated and injected into the power system.

Harmonics in Power Distribution Systems

In electrical power distribution systems, harmonics combine with the fundamental supply frequency to distort voltage and current waveforms. This distortion creates a complex waveform consisting of several harmonic frequencies.

Harmonic frequencies are integer multiples of the fundamental frequency. For example, if the fundamental frequency is 50 Hz:

• 2nd harmonic = 100 Hz
• 3rd harmonic = 150 Hz
• 5th harmonic = 250 Hz

The degree of waveform distortion is directly related to the magnitudes and frequencies of the dominant harmonic components. Generally, low-order harmonics from the 2nd to the 19th order cause the most significant problems, with triplen harmonics (3rd, 9th, 15th, etc.) being particularly harmful.

Definition of Harmonic Frequency

A harmonic is a wave or signal whose frequency is an integral (whole-number) multiple of a reference frequency. The original waveform is known as the fundamental frequency or first harmonic. In a harmonic series, the term harmonic can also refer to the ratio of a signal’s frequency to the fundamental frequency.

Applications of Harmonics

Harmonics are widely used and studied across various fields that involve waveforms and signal processing. Their applications include:

• Electrical power generation and transmission systems
• Electronic and power engineering applications
• Music and audio signal processing
• Radio communication systems
• All technologies that utilize wave-based signals

In all these applications, harmonic frequencies always occur as whole-number multiples of a fundamental frequency.

Conclusion

Harmonics play a crucial role in both beneficial and adverse effects within electrical and electronic systems. While they are essential in applications such as music and communication, excessive harmonics in power systems can cause waveform distortion, equipment malfunction, and efficiency loss. Understanding harmonics is essential for effective power quality management and system design.