Abstract: This invention relates to a residual current device which is able to safely and reliably operate when a line voltage is present (voltage dependent mode) and when the line voltage is not present or falls below a predetermined threshold level (voltage independent mode). The present invention is implemented as a residual current device having a trip mechanism for isolating an electric supply to an electrical installation upon detection of a predetermined current imbalance between the line and neutral conductors of said electric supply. The present invention comprises a current transformer having a secondary winding responsive to any current imbalance on said electrical installation, and a circuit protection winding being connectable to a processing means.

Abstract: This invention relates to a method and apparatus of detecting and compensating for DC residual fault currents on electrical systems. In particular, the present invention relates to a method and apparatus which is capable of accurately detecting one or more parameters of the fault current waveform and generating a compensation factor which compensates for specific pulsed DC fault components present. In this way, trip sensitivity is optimized for all types of fault current waveforms. In a preferred embodiment, the present invention operates by detecting one or more parameters of the encoded fault current waveform and generating a measure of symmetry comparing the mean squared values of negative and positive sections of said encoded fault current waveform. In use, various bands of the ratio of the mean squared sum of the positive and negative sections of said encoded fault current waveform are obtained, and a compensation factor is determined from a look-up table stored in a processing means.

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.

Abstract: This invention relates to a method and apparatus of detecting and compensating for DC residual fault currents on electrical systems. In particular, the present invention relates to a method and apparatus which is capable of accurately detecting one or more parameters of the fault current waveform and generating a compensation factor which compensates for specific pulsed DC fault components present. In this way, trip sensitivity is optimised for all types of fault current waveforms. In a preferred embodiment, the present invention operates by detecting one or more parameters of the encoded fault current waveform and generating a measure of symmetry comparing the mean squared values of negative and positive sections of said encoded fault current waveform. In use, various bands of the ratio of the mean squared sum of the positive and negative sections of said encoded fault current wave-form are obtained, and a compensation factor is determined from a look-up table stored in a processing means.

Abstract: This invention relates to a residual current device which is able to safely and reliably operate when a line voltage is present (voltage dependent mode) and when the line voltage is not present or falls below a predetermined threshold level (voltage independent mode). The present invention is implemented as a residual current device having a trip mechanism for isolating an electric supply to an electrical installation upon detection of a predetermined current imbalance between the line and neutral conductors of said electric supply. The present invention comprises a current transformer having a secondary winding responsive to any current imbalance on said electrical installation, and a circuit protection winding being connectable to a processing means.

Abstract: A residual current device (RCD) protects a circuit by tripping in response to an imbalance signal representative of residual current imbalance in the circuit. The RCD trips the circuit when the imbalance signal exceeds a predetermined threshold rating. The RCD includes a sense coil for generating the imbalance signal and a test coil for introducing a simulation residual current imbalance into the device so as to increase the imbalance signal. A processor monitors the imbalance signal and determines the simulation residual current imbalance required to increase the imbalance signal to a level that corresponds to the predetermined threshold rating so that the sense coil senses the sum of any residual current imbalance in the circuit being protected and the simulation residual current imbalance in order to test operation of the RCD against the predetermined threshold rating.