The term harmonics for decades has been a terminology or a buzz word, making many people reconsider the effectiveness of their building’s wiring system. But over the years, it has shaped new meanings. The presence of harmonics in electrical systems means that the current and voltage are distorted and deviate from sinusoidal waveforms. Harmonics have short and long-term effects on grids, grid connected electronics and power electronics equipment such as malfunction, failure and losses. These reduce reliability, lifetime and efficiency of the electricity networks. Harmonics can also cause overloading of conductors and transformers and overheating of utilisation equipment, such as motors. Harmonic frequencies in the power grid are a frequent cause of power quality problems, and reduction of harmonics optimises productivity, thus, increasing efficiency. Harmonics in power systems result in increased heating in the equipment and conductors, misfiring in variable speed drives, and torque pulsations in motors. Harmonics can also have detrimental effects on transformers, cables, fuses, circuit breakers, lighting, etc. However, technology development has kept pace with demands of the power sector in the country.

Original link: Role of Harmonics Standards

SO WHAT IS HARMONICS ??

The distortion in a sinusoidal wave is generally defined as the content of signal whose frequency is an integral multiple of the fundamental frequency (50Hz.) So given a 50Hz fundamental waveform, this means a 2nd harmonic frequency would be 100Hz (2 x 50Hz), a 3rd harmonic would be 150Hz (3 x 50Hz), a 5th at 250Hz, a 7th at 350Hz and so on.

Complex Waveforms Due To Harmonics

When a sinusoidal voltage is applied to a certain type of load, the current drawn by the load is proportional to the voltage and impedance and follows the envelope of the voltage waveform. These loads are referred to as linearloads (loads where the voltage and current follow one another without any distortion to their pure sine waves). Examples of linear loads are resistive heaters, incandescent lamps, and constant speed induction and synchronous motors.

In contrast, some loads cause the current to vary disproportionately with the voltage during each half cycle. These loads are classified as nonlinear loads, and the current and voltage have waveforms that are nonsinusoidal, containing distortions, whereby the 50Hz waveform has numerous additional waveforms superimposed upon it, creating multiple frequencies within the normal 50Hz sine wave. The multiple frequencies are harmonics of the fundamental frequency.

Examples of nonlinear loads are battery chargers, electronic ballasts, variable frequency drives, and switching mode power supplies. As nonlinear currents flow through a facility’s electrical system and the distribution-transmission lines, additional voltage distortions are produced due to the impedance associated with the electrical network. Thus, as electrical power is generated, distributed, and utilized, voltage and current waveform distortions are produced.

Normally, current distortions produce voltage distortions. However, when there is a stiff sinusoidal voltage source (when there is a low impedance path from the power source, which has sufficient capacity so that loads placed upon it will not effect the voltage), one need not be concerned about current distortions producing voltage distortions.

Original Link: Basic Concepts