Partial Discharge Detection Circuit for Medium-Voltage Switchgear
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Solution Overview
Problem
Current methods for measuring partial discharges in medium-voltage networks require disconnecting the voltage, making it difficult to detect and locate discharges without interrupting the power supply, especially in switchgear configurations where the ground connection is not accessible or is firmly connected to the housing, limiting the effectiveness of HFCT sensors.
Innovation Solution
An electrical circuit arrangement with a frequency response matching resistor and high-pass filter connected to the capacitive voltage testing system, allowing a measuring device with an A/D converter and microprocessor to detect partial discharge pulses at a measuring output of a switchgear, even when the discharges occur further away, and enabling localization without interrupting the voltage supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If HFCT sensors are used for online partial discharge measurement, then partial discharge detection is enabled without disconnecting the voltage, but the measurement is only possible if the cable shield's earth connection is accessible and not permanently connected to the switchgear housing
Solution Approach 1:
The patent introduces an intermediary circuit arrangement that connects between the capacitive voltage testing system and the measuring device. This intermediary interface enables HFCT sensor measurements in switchgear configurations where the earth connection would otherwise be inaccessible or improperly connected, thereby extending applicability to different switchgear types without requiring voltage disconnection
Solution Approach 2:
The measuring device is designed with multi-functional capability to work with both traditional HFCT sensor connections and the new interface circuit arrangement. This universality allows the same measuring device to operate across different switchgear configurations (accessible earth connection, inaccessible earth connection, and permanent housing connection scenarios) without requiring voltage disconnection
2Measurement precision
If a measuring device is connected to the connection socket of a capacitive voltage detecting system, then the device can detect partial discharges in the switchgear area, but it cannot detect partial discharges occurring further away in long cables
Solution Approach 1:
The patent extends the measurement capability from the spatial dimension (local switchgear area) to the temporal dimension by utilizing time-resolved measurements of voltage pulses. By analyzing the time characteristics of pulses traveling along the cable and reflecting from distant partial discharge locations, the system can detect and locate partial discharges in long cables beyond the immediate switchgear area
3Reliability
If the switchgear is de-energized to install HFCT sensors in cases of permanent earth connection to housing, then measurement capability is achieved, but considerable effort and downtime are required
Solution Approach 1:
The patent implements a pre-configured interface circuit arrangement that is already in place within the switchgear, designed to work with HFCT sensors without requiring modification during voltage disconnection. This preliminary preparation eliminates the need for voltage disconnection during sensor installation, as the interface is already adapted to handle various earth connection configurations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables online partial discharge measurements and localization in medium-voltage networks without disconnecting the voltage, improving detection accuracy and safety by extending the frequency range for partial discharge measurements and allowing measurements on long or complexly branched cables.
Implementation Method 1
An electrical circuit arrangement having a frequency response matching resistor connected between an input line, in particular a coaxial line, which serves to connect to the live pole of the measurement output of the capacitive voltage detection system and ground, and a high-pass filter connected downstream of the frequency response matching resistor
Implementation Method 2
a coupling capacitor connected to the live component to be tested, which is connected to the measuring output, usually designed as a connection socket, via a coaxial connecting cable of a defined length
Implementation Method 3
an A/D converter for converting a measured voltage pulse into a digital signal and a microprocessor unit for evaluating the digital signal
Implementation Method 4
If the measuring arrangement is connected at one cable end to a measuring output of a capacitive voltage detection system, the time interval between the voltage pulse traveling directly from the point of partial discharge to the measuring arrangement and the voltage pulse traveling from the point of partial discharge to the remote cable end and reflected back at this remote cable end can be recorded
Data Source
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AI summary
The invention relates to an electrical circuit for connecting an electrical measurement device (16), which is used to measure partial discharges in a power grid having an operating voltage in the range of 1-69kV, and which has an A/D converter (17) for converting a measured voltage pulse into a digital signal and has a microprocessor unit (18) for evaluating the digital signal signal, to a measurement output of a capacitive voltage testing system (3) of a power switching station for the power grid having the operating voltage in the range of 1-69kV. The electrical circuit (8) has a frequency response matching resistor (9) which is connected between an input line (10) for connection to the live pole of the measurement output and to earth, and has a high-pass filter (11) connected downstream of the frequency response matching resistor (9).