Mitigation of Power-Frequency Magnetic Fields With Applications to Substations and Other Parts of the Electric Network
In recent times, electromagnetic emissions from various electrical components have induced more than one debate whether they represent a harmful influence to our health. In addition, interferences caused by power frequency magnetic fields (PFMFs) on electron beam based electronic equipment (e.g. cathode ray tubes found in TV screens and computer monitors, electron microscopes) become evident at levels over 1 microtesla. These issues have caused some concern with the general public but also to the utilities, their customers and the electromagnetic compatibility community. On the other hand, they have also spurred efforts to study and mitigate these fields.
Although most published studies and debates are concerned with fields from power transmission lines, similar levels of PFMFs can be found in a city neighbourhood. For this reason this study focuses on the fields originating from the last stages of the power network before reaching the customer, in particular the components of in-house secondary substations. However the methods developed in this study can also be applied more generally.
Conductive and ferromagnetic shielding, passive and active compensation and other techniques are described. These techniques make use of modern methods of analysis such as algebraic computing and 2D/3D modelling. It was found that shielding using thin conductive plates and a proper design can provide for cost-effective mitigation of PFMFs. It was shown that the choice of either ferromagnetic or conductive shielding is dependant on a number of variables, which can only be determined by a proper 2D or 3D modelling. It was also found that cable and busbar connections and not the transformers are the main cause of large PFMF emission from substations.
These and other results were applied to actual cases where the measured values were considered as problematic, or where low emission was a requirement already at the design stages.
power-frequency magnetic fields