The effect of some winding defects, Part 1

ABSTRACT: An ideal, perfectly-wound Rogowski coil should respond only to currents which thread the coil. It should not matter if the current-carrying conductor is off axis or threads the coil obliquely. Furthermore, the coil should have zero response to electric currents and other sources of magnetic fields which are external to the loop of the coil. These properties follow as a consequence of Ampere’s Law.

In a 'real' coil there are inevitably winding defects and the ideal properties described above cannot be achieved in practice. This Note describes a simple method for determining how winding defects can affect the performance of a coil. The method can be used for accurate calculations as well as providing a method for making qualitative estimates without the need for mathematical analysis. For de-mountable coils, such as flexible coils and split-rigid coils, the most significant potential defect is the inevitable gap in the winding where the coil is opened so that it can be placed round the conductor. The method described for calculating the effect of winding defects, such as a gap, is illustrated by a number of examples and is compared with some actual measurements on coils.