Patent ID: 8901941

Claim:
An instrument ( 1 ) for detecting partial electric discharges in an electric apparatus ( 2 ), when said apparatus ( 2 ) is connected to a measuring circuit having a direct-measuring impedance device ( 7 ) connected across a low-voltage terminal of the electrical apparatus ( 2 ) and an earth node ( 4 ), and an indirect-measuring impedance device ( 8 ) connected across the earth node ( 4 ) and a low voltage terminal of a coupling capacitor ( 6 ) connected in parallel to the electrical apparatus ( 2 ), the instrument ( 1 ) wherein it comprises: a first LF input stage ( 19 ) designed to receive an analogue signal ( 10 ) picked up at the terminals of the direct-measuring impedance device ( 7 ) and representative of electrical pulses correlated with the partial discharges, and to output a first LF digital signal ( 20 ) forming an uninterrupted sample flow representative of the pulses, the first LF input stage ( 19 ) forming a detection bandwidth of less than 2 MHz; a first LF acquisition unit ( 27 ) connected to the first LF input stage ( 19 ) for receiving the first LF digital signal ( 20 ), and to a trigger module ( 14 ) for receiving a control signal ( 15 ) designed to allow samples of said flow to be selected according to a predetermined criterion, and configured to select from the flow of samples groups of samples forming segments corresponding to individual electrical pulses as a function of the control signal ( 15 ), thus generating a first LF digital acquisition signal ( 34 ); a second LF input stage ( 19 A) designed to receive an analogue signal ( 32 ) picked up at the terminals of the indirect-measuring impedance device ( 8 ) and representative of electrical pulses correlated with the partial discharges, and to output a second LF digital signal ( 20 A) forming an uninterrupted sample flow representative of the pulses, the second LF input stage ( 19 A) forming a detection bandwidth of less than 2 MHz; a second LF acquisition unit ( 27 A) connected to the second LF input stage ( 19 A) for receiving the second LF digital signal ( 20 A) and designed to receive the control signal ( 15 ) which allows samples of said flow to be selected according to a predetermined criterion, and configured to select from the flow of samples groups of samples forming segments corresponding to individual electrical pulses as a function of the control signal ( 15 ), thus generating a second LF digital acquisition signal ( 34 A); a processing block ( 35 ) designed to receive the first and second LF digital acquisition signals ( 34 , 34 A) to generate a balanced digital signal ( 36 ) without components representative of common mode electrical signals present in the measuring circuit; an output stage ( 17 ) designed to receive the balanced digital signal ( 36 ) and to allow processing thereof.