WHAT ARE HARMONICS?

Harmonics are currents, usually in multiples of the supply fundamental frequency, produced by ‘non-linear’ loads such as the AC to DC power conversion circuits.For example, on a 50Hz supply, the 5th harmonic is 250 Hz, 7th harmonic is 350 Hz, etc. These are called ‘integer harmonics’ - i.e. exact multiples of the supply frequency. These power conversion circuits draw only short pulses of current from the supply network and combine with the source impedance resulting in distortion of the supply voltage.

Harmonic effects

The main effects of voltage and current harmonics within the power system are:-

• Amplification of harmonic levels resulting from series and parallel resonance;
• Reduction of efficiency of power generation, transmission, and utilization;
• Aging of the installation of electrical plant components and as a consequence the shortening of their useful life;
• Plant mal-operation;
• Malfunctioning and failure of electronic equipment;
• Overheating and failure of electric motors;
• Overloading, overheating and failure of power factor correction capacitors. Resonance due to interaction of capacitors with harmonics;
• Overloading and overheating of distribution transformers and neutral conductors;
• Excessive measurement errors in metering equipment;
• Spurious operation of fuses, circuit-breakers and other protective equipment;
• Voltage glitches in computers systems resulting in lost data. Excessive flicker on VDU's;
• Electromagnetic interference with TV, radio, communication & telephone systems;
• Damage and disruption to standby generators and associated AVR control equipment;
• Interference with ripple control systems.