Method and an apparatus for monitoring an activity of partial electrical discharges in an electrical apparatus powered with direct voltage

A method for monitoring an activity of partial electrical discharges in an electrical apparatus powered with direct voltage,

• characterised in that it comprises the following steps, repeated in succession at predetermined time intervals:
• measuring (1), with a sequence of acquisitions repeated over time, analogue electrical signals detected by a sensor operatively coupled to the apparatus and generating corresponding digital signals representative of the wave forms of said analogue signals, thus providing a plurality of data sets acquired through the same sensor at successive steps separated by said predetermined time intervals;
• deriving (2), for each of said digital signals, at least one shape parameter correlated to the wave form of that signal and at least one amplitude parameter correlated to the amplitude of that signal, wherein, for each of said digital signals, a first shape parameter, correlated to the time duration of the signal, and a second shape parameter, correlated to the frequency content of the signal, are derived;
• separating (3) a set formed by said measured digital signals into sub-sets, so that the digital signals of each sub-set have similar values of the shape parameter, wherein signals positioned in a same region of a reference plane having said first and second shape parameter as co-ordinates are grouped in a same sub-set;
• correlating (4) the sub-sets of signals having similar values of the shape parameter and measured in successive steps at said predetermined time intervals, defining correlated groups of sub-sets, thus making available groups of sub-sets of signals measured in different acquisitions but having similar wave forms, wherein said correlated sub-sets belong to corresponding data sets separated by said predetermined time intervals;
• selecting (5) any correlated groups of sub-sets having similar values of the shape parameter for which the amplitude parameter has a predetermined profile exhibiting an increase over time and attributing the signals of said sub-sets to partial discharge activities, wherein the correlated sub-sets for which the amplitude parameter has an increasing profile over time are attributed to partial discharge activities, wherein the trend of the amplitude parameter as a function of time is assessed.