When the audio system whistles

Problem: Potential equalisation currents

Potential equalisation currents, often referred to as vagrant currents, are not only a problem in industrial plants. Currents can also have a disruptive effect on equipotential bonding in commercial and even residential buildings.

Cause: Leakage currents frequency inverter

The picture shows the cause of an annoying whistling in the speakers of a home stereo system. These are leakage currents of an inverter drive that must flow back to the transformer star point due to their characteristics. They always occur when a corresponding filter on the inverter is missing or defective. Common-mode voltage distortions of the phase-to-earth voltages then occur at the clock frequency at the inverter output. These clock frequency currents are then detectable at the equipotential bonding of the entire building and also at the disturbed audio system.

Solution

Retrofitting and EMC-compliant installation of an effective filter.

Impressum
PQ Professionals GmbH 
Landsberger Straße 4 
04157 Leipzig 
vertreten durch den GF Dipl.-Ing. (FH) Frank Strobel