Application Note Current harmonics Problem - The influence of current harmonics on equipment connected to electrical supply systems can cause serious problems. What is a Harmonic The typical definition for a harmonic is: a sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency. Consequences of high current harmonics - Harmonics cause circuit breakers tripping at no apparent overload. - Voltage waveforms to other loads can be distorted and interference can be inductively coupled between power and low-voltage communication lines if they are placed close to each other. - Harmonics that flows back to the supply network can have various negative effects. In case 5th harmonic is highly present 3-phase inductive motors can ex perience “torque fight” as this component cause the negative torque that tends to turn the motor backwards. Consequently more power is consumed and the motor gets gradually overheated. - High harmonics reduce the “transmission” capacity of the supply network, as they do not perform any useful work. - High neutral conductor currents are also a consequence of high current harmonics. Thus a neutral conductor cross-section has to be larger or there is a significant risk of fire. - High current harmonics supplied back to the network may influence the harmonics content on the supply voltage, which in the next step result on unwanted current harmonics on the end-user equip

High content of harmonic components Harmonic components are one of major power quality concerns. Non-linear loads like electronic ballasts, UPS systems, variable frequency drives and switch mode power supplies all create distortion of the sinusoidal waveform. Distorted signal is analysed with Fast Fourier Transformation (FFT) calculation method. Basic signal with a fundamental frequency 50/60Hz is reported together with individual harmonic components. There are some representative examples how and when certain harmonics appear. Computers, printers and other small office IT equipment High 3rd,...

Preventive and corrective actions - When purchasing and installing new equipment it is recommended that the “low content THD” is selected. - Neutral conductor in a 3-phase system has to be sized in respect with current harmonics content as well. It sometimes means the cross-section of the neutral conductor has to be larger than the phase conductor’s. - In order to limit current harmonics active or passive filters are used. They will damp unwanted harmonics down to acceptable level. The PQA Master instruments are designed in accordance with the following standards: IEC 61000-4-30 Class A/S Part...