Abb Research Ltd.

Henrik Johansson

Tord Bengtsson

Stefan Roxenborg

Joseph Menezes

Stefan G Thorburn

Mikael Sehlstedt

Zoltan Nagy

Roland Braun

Morgan Johansson

Lars Kalland

A method for adapting a ground fault detection to a change of an electrical machine condition, wherein the machine includes a winding. The electrical machine is in a first machine condition, a first reference value being defined for measured values of an electrical quantity. The ground fault detection includes continuously measuring the electrical quantity in the winding and detecting a ground fault based on the measured values of the electrical quantity and the first reference value. The method includes receiving a signal, detecting a change of machine condition based on the received signal, and changing to a second reference value for the measured values of the electrical quantity, the second reference value being different from the first reference value when the change of machine condition is detected.

Method for adaptation of ground fault detection

A method for linearizing voltage transmission through a transformer including a magnetic core and, input and output windings. A measurement signal is supplied to the input winding at a first frequency and an output signal is measured at the output winding of the transformer, wherein the voltage of the measurement signal may be so low that the transformer operates in a non-linear region. The method includes, for a conditioning signal, selecting a second frequency different from the first frequency, defining an amplitude value of the conditioning signal and supplying the conditioning signal to the input winding at the second frequency with the defined amplitude value so that the transformer operates in its linear region.

Method and device for linearizing a transformer

A method for enhancing the reliability of generator ground fault detection based on a signal injection scheme, wherein the generator includes a winding. The method includes injecting a test signal at a predefined frequency to the winding, measuring an electrical quantity of a response signal in the winding resulted from the injected test signal, and detecting a ground fault based on the measured value of the electrical quantity. The method further includes continuously determining the frequency of the response signal, and discarding the present measured value corresponding to the determined frequency when the determined frequency deviates from the predefined frequency with a first threshold value.

Method and device for enhancing the reliability of generator ground fault detection on a rotating electrical machine

A method and a device for supervising the sensitivity of a protection function in an electrical power system including a metering device for measuring values of a feature, said protection function being configured to initialize an action based on a test value and a threshold value for the feature, wherein said test value is either a measured value or derived from the said measured values, the device includes a computing unit configured to receive the test values and, repeatedly during the operation of the protection function, to calculate a mean value and a deviation of the test values, to determine the probability of a false action based on the calculated mean value, the threshold value and the calculated deviation, and to indicate that the sensitivity is too high when the probability of a false action exceeds a first limit value for the probability of a false action.

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Vasteras, Sweden

Henrik Johansson