Method and arrangement for detecting partial discharges in an electric operating means

1. A method for detecting partial discharges for an electrical apparatus, comprising:

capturing electromagnetic pulses with a sensor device,

selecting a narrow frequency band from a frequency spectrum of the electromagnetic pulses with a filter device,

amplifying the narrow frequency band each time with an amplifier device,

comparing signals contained in the narrow frequency band with a threshold value for the amplitude with a comparison device, wherein a partial discharge is detected when the threshold value is exceeded; and

wherein an analog signal representing a detected partial discharge is converted into a digital pulse by means of a flipflop output, wherein the digital pulse is further processed to indicate occurrence of the partial discharge,

wherein the sensor device comprises an internal sensor device to detect internally-based interference signals and an external sensor device to detect externally-based interference signals, and wherein if both the internal and the external sensor devices receive an electromagnetic signal then the electromagnetic signal is an externally-based interference signal and is not further processed according to the method.

2. The method as claimed in claim 1 ,

wherein the flipflop output used is a Schmitt trigger.

3. The method as claimed in claim 1 ,

wherein a sample-and-hold element is used to extend the duration of the signal.

4. The method as claimed in claim 1 ,

wherein analog electrical circuits are used each time for the sensor device, the filter device, the amplifier device, the flipflop output, a sample-and-hold element and the comparison device.

5. The method as claimed in claim 1 ,

wherein the electromagnetic signals are captured in a frequency range up to 2 GHz and in that a frequency width of no more than 200 MHz is used for the narrow frequency band.

6. The method as claimed in claim 1 ,

wherein a gas-insulated electrical switchgear unit is used for the apparatus.

7. An arrangement for detecting partial discharges for an electrical apparatus, comprising:

a sensor device for capturing electromagnetic signals,

a filter device designed to select a narrow frequency band from a frequency spectrum of the electromagnetic signals,

an amplifier device designed to amplify the narrow frequency band each time,

a comparison device designed to compare signals contained in the narrow frequency band with a threshold value for the amplitude, wherein a partial discharge is detected when the threshold value is exceeded, the partial discharge represented by an analog signal; and

a flipflop output for converting the analog signal into a digital pulse, wherein the digital pulse is further processed to indicate occurrence of the partial discharge,

wherein the sensor device comprises an internal sensor device to detect internally-based interference signals and an external sensor device to detect externally-based interference signals, and wherein if both the internal and the external sensor devices receive an electromagnetic signal then the electromagnetic signal is an externally-based interference signal and is not further processed by the arrangement.

8. The arrangement as claimed in claim 7 ,

wherein the flipflop output comprises a Schmitt trigger.

9. The arrangement as claimed in claim 7 , further comprising:

a sample-and-hold element for extending the duration of the signal.

10. The arrangement as claimed in claim 7 ,

wherein the sensor device, the filter device, the amplifier device, the flipflop output, a sample-and-hold element and the comparison device are each in the form of analog electrical circuits.

11. The arrangement as claimed in claim 7 ,

wherein the electromagnetic signals have a frequency range of up to 2 GHz and in that the narrow frequency band has a frequency width of no more than 200 MHz.

12. The arrangement as claimed in claim 7 ,

wherein the apparatus comprises a gas-insulated electrical switchgear unit.