Description of magnetic field distributions caused by single-pole encapsulated switchgear

Power frequency magnetic fields produced by switchgear might interfere with sensitive equipment or might even conflict with exposure limits for people. In order to prevent possible influences the knowledge of the magnetic field levels at locations under concern is necessary. Though the magnetic field distributions of switchgear installations are mainly determined by the physical arrangement of the conductor bus bars, in the case of single-pole encapsulated switchgear, however, these fields are significantly affected by the propagation of sheath currents on the encapsulation. This paper outlines investigations concerning the creation of sheath currents and their contribution on the resulting magnetic fields caused by the switchgear. Numerical simulations were performed on the basis of the method of moments which take into account the induction of sheath currents. Based on those results a concept is described which is suitable to determine minimum distances to be used between switchgear and areas under concern. This method avoids that every individual switchgear installation has to be investigated in detail. It rather allows derivation of magnetic field strength distributions on the basis of the switchgear type independent of the actual configuration.