John G. Buchan PhD.pdf - OpenAIR @ RGU - Robert Gordon ...

i. Sensitivity depends on the permeability of the magnetic core andany air gap in the iron path severely reduces the current transformer'soutput .It is therefore necessary to machine the faces of the coreat the slit position, and to provide an adequate clamping arrangement.ii. Power frequency currents in the secondary winding are high andwill subsequently affect the amplifier stage.A device which is gaining acceptance as a partial discharge coupleris the Rogowski coil. The Rogowski coil is basically an air-coredcurrent transformer and consequently requires a large number of turnsto provide comparable sensitivity .It has the advantage of a simpleconstruction, since it may be wound-on any non-magnetic former, andexhibits superior power frequency signal rejection. These usefulqualities of the Rogowski coil makes it desirable for use in adischarge detection system.Most publications have examined the behaviour of the Rogowski coil asa current monitor in measurement" systems involving high-energyelectron beams [83]. The following sections represent a detailedinvestigation on the theory and application'of the Rogowski coil inpartial discharge detection.3.2 The Rogowski CoilThe Rogowski coil, sometimes referred to as the Rogowski loop, is adevice which allows non-intrusive measurement of fast rise-time pulsedcurrents [83,84,85][86]..It was first developed by W. Rogowski in 1912As its name suggests, the Rogowski coil is essentially a thin solenoidbent round to form a closed loop, normally a toroid, making anaperture through which the current to be measured is passed. -Avoltage is electromagnetically induced in the coil by any time varyingcurrent threading the loop aperture which, provided the coil isproperly terminated, is an analogue of the current pulse.TheRogowski, coil offers distinct advantages over other currentmonitoringdevices in that:The loop is only sensitive to currents that thread the"aperture, and aPage 131