Abstract: This invention relates to a method and apparatus for executing secondary functions on an electrical switchgear device. In particular, the present invention relates to a method and apparatus which is implemented in the processing electronics of an electrical switchgear device which has a primary trip or protection function and also the capability to execute secondary functions or applications, such as over/undervoltage conditions and near fault warning levels and display. These secondary functions or applications being user configurable and are subject to processing availability and the constraints of the primary protection function.

Abstract: This invention relates to a nulling current transformer. More particularly, this invention relates to a nulling current transformer for accurately detecting current and giving an improved response, accuracy and stability using toroidal current transformer technology along with active components. This invention finds particular application in switchgear devices such as residual current devices and metering operations. The nulling current transformer is implemented in a closed magnetic core having at least one primary winding inductively coupled thereto. A secondary winding is also inductively coupled to said magnetic core, the secondary winding being responsive to any magnetic flux generated in said magnetic core. A separate tertiary winding is also inductively coupled to said magnetic core, the tertiary winding being responsive to any magnetic flux generated in the magnetic core.