Abstract: A method of monitoring voltage stability within an electrical power system comprises the steps of establishing a dynamic power system stability margin based on an operating characteristic of the power system; indicating that the power system has become unstable when the dynamic power system stability margin falls below a predetermined value; and initiating dynamic load shedding and/or restoration depending on stability margin.

Abstract: In the field of current differential protection relays there is a need for improvements in or relating to the protection relays to allow them to accommodate current transformer saturation while maintaining a desired degree of reliability. A method of operating a current differential protection relay following a fault, the protection relay being electrically coupled to a protection zone of an electrical power system, comprises the steps of establishing a fault condition by discriminating between an internal fault inside the protection zone and an external fault outside the protection zone; and modifying the sensitivity of the protection relay according to the nature of the fault condition.

Abstract: A sampling module, for sampling one or more analog characteristics of a power transmission system, including at least one input circuit for sampling a respective analog characteristic. Each input circuit includes: a scaling circuit for reducing the magnitude of the analog characteristic to a desired level; an isolating circuit for creating an electrical barrier between respective upstream and downstream portions of the input circuit; and an analog to digital converter for digitizing the analog characteristic to produce a digital data stream. The scaling circuit is electrically connected to an input of the analog to digital converter, and the isolating circuit is electrically connected directly to an output thereof.

Abstract: A sampling module, for sampling one or more analog characteristics of a power transmission system, including at least one input circuit for sampling a respective analog characteristic. Each input circuit includes: a scaling circuit for reducing the magnitude of the analog characteristic to a desired level; an isolating circuit for creating an electrical barrier between respective upstream and downstream portions of the input circuit; and an analog to digital converter for digitizing the analog characteristic to produce a digital data stream. The scaling circuit is electrically connected to an input of the analog to digital converter, and the isolating circuit is electrically connected directly to an output thereof.

Abstract: A method of monitoring voltage stability within an electrical power system comprises the steps of establishing a dynamic power system stability margin based on an operating characteristic of the power system; indicating that the power system has become unstable when the dynamic power system stability margin falls below a predetermined value; and initiating dynamic load shedding and/or restoration depending on stability margin.

Abstract: In the field of current differential protection relays there is a need for improvements in or relating to the protection relays to allow them to accommodate current transformer saturation while maintaining a desired degree of reliability. A method of operating a current differential protection relay following a fault, the protection relay being electrically coupled to a protection zone of an electrical power system, comprises the steps of establishing a fault condition by discriminating between an internal fault inside the protection zone and an external fault outside the protection zone; and modifying the sensitivity of the protection relay according to the nature of the fault condition.

Abstract: A method of supervising the operation of a plurality of current transformers arranged in respective groups and connected to a protection relay forming part of a three-phase electrical power system includes determining a current ratio at an output of each group of current transformers, comparing each current ratio with a predetermined high ratio, comparing each current ratio with a predetermined low ratio, and generating a fault indication when the current ratio at one location exceeds the predetermined high ratio and the current ratio at the or each other location remains below the predetermined low ratio.