Method for processing data pertaining to an activity of partial electrical discharges
A method for measuring and processing data pertaining to an activity of partial electrical discharges taking place in a three-phase electric machine ( 1 ) powered with square wave voltage, said data comprising a plurality of discharge signals and a plurality of sets of three values (e u , e v , e w ) of power supply voltage of the machine measured in concurrence with a corresponding discharge signal, comprises the following steps: —transforming each set (e u , e v , e w ) of three voltage values measured into a corresponding pair (e d , e q ) of voltage values; —deriving a phase angle value from each of said pairs (e d , e q ) of voltage values; —attributing to each discharge signal the corresponding phase value, to assess the measured discharge signals as a function of corresponding phase values. Prior art techniques for processing data pertaining to activity of partial electrical discharges taking place in three phase electric machines powered with square wave voltage provide for assessing the measured discharged signals as a time sequence of events, with no possibility to place them effectively in relation to the power supply voltages, this entailing that any subsequent statistical processing of the measured data will have little significance.
1. A method for processing data pertaining to an activity of partial electrical discharges taking place in a three-phase electric machine ( 1 ) powered with square wave voltage by a power converter ( 2 ), for the purpose of assessing for diagnostic purposes the activity of partial discharges taking place in the machine ( 1 ), said data comprising a plurality of discharge signals associated with said partial electrical discharges and a plurality of sets of three values (e U , e V , e W ) of power supply voltage of the machine ( 1 ), each set measured in concurrence with a corresponding discharge signal,
wherein said method comprises the following steps:
transforming each set (e U , e V , e W ) of three voltage values measured into a corresponding pair (e d , e q ) of voltage values;
deriving a phase angle value from each of said pairs (e d , e q ) of voltage values, the derived phase angle values being in relation to logic states of the converter ( 2 );
attributing to each discharge signal associated with a corresponding partial electrical discharge the corresponding phase angle value, to assess the measured discharge signals as a function of corresponding phase angle values.
2. The method as claimed in claim 1 , wherein said three phase electric machine ( 1 ) is powered by a converter ( 2 ) operating in PWM logic.
3. The method as claimed in claim 1 , wherein said transformation step comprises multiplying each measured set of three voltages (e U , e V , e W ) times a predetermined matrix, able to remove from said set of three voltages the zero sequence component.
4. The method as claimed in claim 3 , wherein said predetermined matrix is a matrix obtainable multiplying a Park matrix times any 2×2 matrix of maximum rank.
5. The method as claimed in claim 1 , comprising a step of separating the discharge signals into classes on the basis of the respective attributed phase values.
6. The method as claimed in claim 5 , wherein said classes are three and correspond to predetermined phase intervals.
7. The method as claimed in claim 6 , wherein said phase intervals are substantially the following:
[85, 95] and [215, 325] for the first class;
[205, 215] and [335, 85] for the second class;
[325, 335] and [95, 205] for the third class.
8. The method as claimed in claim 1 , comprising a step of statistically processing the values of amplitude of the discharge signals as a function of the phase values attributed.
9. The method as claimed in claim 5 , comprising a step of statistically processing the values of amplitude of the discharge signals of a predetermined class, as a function of the phase values attributed.
10. The method as claimed in claim 1 , comprising a step of rejecting noise, on the basis of said phase values attributed to the discharge signals.
11. The method as claimed in claim 1 , wherein said plurality of discharge signals is measured through a sensor ( 3 ) common to all three phases.
12. A method for assessing for diagnostic purposes an activity of partial electrical discharges taking place in a machine ( 1 ) powered with square wave voltage by a power converter ( 2 ), the method comprising, for the measurement of the data to be processed, the following steps:
measuring a plurality of discharge signals, associated with said partial electrical discharges;
measuring a set of three values of voltage (e U , e V , e W ) powering the machine, in concurrence with each measured discharge signal;
processing data comprising said plurality of discharge signals associated with said partial electrical discharges and said plurality of sets of three values (e U , e V , e W ) of power supply voltage of the machine ( 1 ), each set measured in concurrence with a corresponding discharge signal, wherein
the processing of said data comprises the following steps:
transforming each set of three voltage values measured into a corresponding pair of voltage values (e d , e q );
deriving a phase angle value from each of said pairs of voltage values, the derived phase angle values being in relation to logic states of the converter ( 2 );
attributing to each discharge signal the corresponding phase value, to assess the measured discharge signals as a function of corresponding phase values.