Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Gaseous discharge
Reexamination Certificate
2000-06-21
2001-07-03
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Gaseous discharge
C324S551000, C324S536000, C250S206100, C370S540000
Reexamination Certificate
active
06255808
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for measuring partial discharges in gas-insulated high voltage facilities, having a first calibratable sensor suitable for measurement in the HF range and a second sensor suitable for detecting signal components characteristic of partial discharges, in particular for measurement in the UHF range, arranged inside a metal enclosure, having a first branch for processing an HF signal component and a second branch for processing a UHF signal component as well as having a gate device connected to the first and second sensors.
BACKGROUND INFORMATION
European Patent Application 488 719 A2 describes a device and a method of detecting partial discharges in gas-insulated high voltage facilities (see FIG. 6 there), where a fundamental frequency and an HF component below a few hundred kHz, possibly generated by interference, are picked up. These signal components can be separated using filter devices. The signals thus obtained are converted to a form suitable for further processing by using filter devices and sent to a computer system. The signal obtained in the high frequency range below a few hundred kHz is used to identify external interference. The zero crossing of the high voltage acts as a trigger signal for the start of the partial discharge measurement. Partial discharge signals in the range of a few 10 MHz are recorded by a second sensor and processed further in a suitable signal processing branch for identification of the partial discharges. With the wiring described there, this sensor is operated at a few 10 MHz in antenna mode and thus cannot be calibrated for partial discharge measurements.
In this connection, the HF range should be understood to be the frequency range between a few 10 kHz and 100 MHz and the UHF range should be understood to be the frequency range above 100 MHz.
German Patent Application 195 48 466 A1 describes a device the gate is blocked when there is a measurement signal from a sensor, with the input signal for controlling the gate being an HF (High Frequency) signal below 10 MHZ, for example. The signal allowed through by the gate for further processing may be a broad-band UHF signal in the range up to 1.5 GHz, for example. In this way, interference in measurement of partial discharges is to be avoided. However, no calibrated measurement is provided with this system.
SUMMARY
An object of the present invention is to improve upon the reliability of measurement of partial discharges while at the same time permitting a calibrated measurement.
This object is achieved according to the present invention by the fact that the gate device is actuated in the presence of a UHF signal component characteristic of a partial discharge, and when actuated, it allows the HF signal component to pass through for further processing.
The use of a first calibratable sensor allows a very accurate and reproducible measurement result to be achieved in a partial discharge measurement. Such a sensor may have, for example, a measuring electrode for capacitive coupling to a high voltage conductor arranged in the high voltage facility. The second sensor, which is wired for and suitable for the UHF range, cannot be calibrated due to its external wiring, but it functions as a detector for partial discharges in conjunction with the first sensor. The second sensor merely supplies information about the existence or non-existence of a partial discharge and actuates the gate device accordingly. No calibration of the second sensor is necessary. For example, such a UHF sensor may have an antenna for detection of electromagnetic radiation or it may have a device which detects a signal component that is typical of partial discharges by some other method, e.g., a chemical, optical or acoustic method. Due to the use of two sensors, a first sensor which is active in the HF range and a second sensor which is active in the UHF range, and due to the two-branch design, the required signal processing for reliable measurement of partial discharges is implemented on a sensor level. The gate device is suitable for controlling the interaction of the UHF signal component and the HF signal component. Opening of the gate device for a certain period of time can be prompted, or optionally the duration of opening of the gate device during which the HF signal component is transmitted for further processing can be determined by a second input (control input) through the UHF signal component.
On exposure to external interference which cannot be attributed to a partial discharge, a UHF signal component which is optionally present intrudes the high voltage facility only with great damping, so that in this case the gate device is not actuated. The gate device is not opened until a certain signal threshold is exceeded.
In an advantageous embodiment of the present invention, the first and the second sensors may be in direct proximity to one another.
In this way, both sensors receive the same signal with regard to both time and space without allowing various distortions of the signal to occur.
In another advantageous embodiment of the present invention, a cone antenna may be provided as a UHF sensor.
Because of their design, cone antennas are especially suitable for measuring UHF signals.
For example, cylindrical electrodes which surround the high voltage conductor concentrically are suitable for measuring HF signals.
A single sensor may also be provided to advantage as a receiver for both UHF and HF signals.
Additional sensors may be eliminated by using just one broad-band sensor. This sensor must then be operable simultaneously in both the HF range (capacitive operation) and in the UHF range (antenna operation) due to appropriate wiring with two signal processing branches.
In a method for measuring partial discharges in gas-insulated high voltage facilities, a UHF signal component and an HF signal component are received within an enclosure, and if there is a UHF signal component exceeding a certain threshold, a gate element is actuated to transmit the HF signal component for further processing.
This separate detection of a UHF signal component and an HF signal component yields a signal separation based on the frequency band directly after signal pickup. The UHF signal component thus obtained is used as a control signal to open the gate device through which the HF signal is allowed to pass.
The present invention may be implemented using a programmable computer equipped with analog inputs. HF and UHF signal components picked up by the sensors go to the computer via the analog inputs. A computer program processes and weights the signal components and displays the result on a monitor or a screen.
One embodiment of the present invention is described below with reference to the drawing and its functioning is explained.
REFERENCES:
patent: 4411019 (1983-10-01), Rypkema
patent: 4763327 (1988-08-01), Fontaine et al.
patent: 5146170 (1992-09-01), Ishikawa et al.
patent: 5168152 (1992-12-01), Kelley
patent: 5396180 (1995-03-01), Hampton et al.
patent: 5485347 (1996-01-01), Miura
patent: 5569840 (1996-10-01), Thuries
patent: 5793336 (1998-08-01), Shoemaker et al.
patent: 195 48 466 (1997-06-01), None
patent: 0 488 719 (1992-06-01), None
patent: 0 699 918 (1996-03-01), None
patent: 0 780 692 (1997-06-01), None
patent: 230 214 (1996-11-01), None
patent: 8317087 (1996-11-01), None
Hampton et al. “Diagnostic measurements at UHF in gas insulated substations” pp. 137-144, Mar. 1988.
Brown Glenn W.
Hamdan Wasseem H.
Kenyon & Kenyon
Siemens Aktiengesellschaft
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