An embodiment of the invention relates to a method for ground fault detection for low-voltage three-phase AC circuits having a neutral conductor, in which first to fourth analog current signals of the first to third phase conductors and of the neutral conductor of the three-phase AC circuit are ascertained that each contain the level or an equivalent of the level of the current. The analog current signals are time-division multiplexed, subjected to a/d conversion, and a sequence of time-division-multiplexed first to fourth digital current values present in first to fourth successive time frames form first to fourth current signals. Three of the four digital current signals are interpolated to ascertain interpolated current values. The current value of the time frame of the uninterpolated current signal and the interpolated current values for the time frame of the uninterpolated current signal are used for discovering the ground fault.

A method for protecting a low-voltage distribution network. The low-voltage distribution network includes a low-voltage side of a three-phase distribution transformer that is configured to supply electrical power to at least one single-phase load through a respective distribution line of a plurality of three-phase distribution lines distribution lines. The method includes measuring variations of a periodic neutral-to-ground voltage between a neutral terminal of the three-phase distribution transformer and a local ground node by sampling the variations at a sampling frequency, detecting a fault in the low-voltage power distribution network based on the variations of the periodic neutral-to-ground voltage, and disconnecting the low-voltage side from the low-voltage power distribution network responsive to the fault being detected.

Fault classification and zone identification in a power transmission system are described. Voltage or current measurements are obtained at a terminal of the transmission line in each of the three phases measured during a fault. Modal transformations are performed on voltage or current measurements to obtain traveling wave signals with reference to each of the three phases. Based on the magnitude of the traveling wave signals the fault is classified.

The invention discloses a method for identifying full parameters of an electric element by a fault recording data, comprising steps: inputting fault recording data related to an electric element; conducting data processing on the fault recording data; identifying full parameters of the element by intercepted data and a differential equation of the full parameters of the element; and outputting an identified result. Further proposed are a system for identifying full parameters of a power generator by fault recording data and a method for locating a line fault point with fault recording data. With the implementation of the invention, a fault resistance and full parameters of an element such as an electric line and a transformer, etc. can be identified. The invention can obtain full parameters of a fault element and also a non-fault element, and the parameters precision would be increased from the current 20% to less than 1%.

A method and an apparatus for detecting a vector shift in an AC power system, the apparatus comprising frequency measuring means adapted to determine a frequency of the AC power system, derivation means adapted to determine a time derivative of the frequency, filtering means adapted to filter the time derivative of the frequency, and detection means adapted to calculate time derivatives for the filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system, to determine a number of positive and negative time derivatives among the calculated time derivatives, and to detect a vector shift in the AC power system in response to an absolute value of a difference between the determined number of positive time derivatives and negative time derivatives exceeding a predetermined threshold value.