Harmonic Filter CHARM

Most types of equipment common in electrical systems today generate harmonics:

• Equipment containing electronics that control other apparatus, e.g. variable speed drives, soft starters, static compensators, rectifiers, etc.
• Arc furnaces
• In certain cases, transformers, reactors and rotating machines.
• Home electronic appliances.

Harmonics are not only found in industrial networks. They can also spread into the distribution network and cause problems for other power users.

Distorted sinus curve
Harmonics become apparent when a distorted sinus curve is mathematically analysed. Through Fourier analysis, an arbitrary periodic function can be divided into a number of sine waves. The example below shows that the distorted curve consists both of the fundamental frequency (e.g. 50 Hz) and of super-imposed 5th (250 Hz) and 7th (350 Hz) harmonic frequencies.

	+		+		=
50 Hz		5th (250 Hz)		7th (350 Hz)		Distorted curve

Problems caused by harmonics:

• Increased losses, e.g. machines will operate at increased temperature and can be overheated. Their lifetime will be reduced.
• Excitations of resonances
• Malfunctioning of control systems since electronic meters, relays, etc. are matched to the fundamental frequency
• Overloading of capacitors, leading to malfunctioning and premature aging
• Interference with telecommunications and computers
• Disturbances in ripple control systems
• High currents in neutral conductors.

Designing a harmonic filter
A passive harmonic filter typically consists of a capacitor which is connected in series with a reactor. The components are dimensioned to create a series resonance circuit for a required frequency. A harmonic filter works like a short circuit at one or more specified frequencies. We can help you to calculate and design filters which will reduce interference and interruption on your network.