AC Voltage Marking for Ground Fault Location
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Solution Overview
Problem
Existing methods for locating ground faults in power cables, especially those laid underground, require disconnecting cables from the mains and applying DC voltage, leading to significant downtimes and interference with connected consumers due to the use of continuous AC voltage markings.
Innovation Solution
A method using AC voltage with selectively marked individual half-waves, allowing for pinpointing of ground faults without disrupting normal power supply operations by minimizing interference, and enabling the use of existing mains voltage for measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC voltage is applied to the cable for fault location measurement, then directional information and measurement precision are improved, but the cable must be completely disconnected from the mains causing significant downtime and interference with connected consumers
Solution Approach 1:
The patent changes the voltage type parameter from DC to AC, allowing measurements to be performed on live cables without disconnection. The AC voltage enables step voltage measurement while maintaining power supply continuity, thus improving the time parameter while preserving measurement capability through parameter transformation
Solution Approach 2:
The patent applies periodic AC voltage instead of continuous DC voltage. By using the zero-crossing points of the AC waveform as measurement triggers, the system achieves directional fault location information without requiring cable disconnection, thereby reducing downtime while maintaining measurement precision through periodic sampling at appropriate phases
2Productivity
If continuous AC voltage marking is used for fault location, then the cable remains connected to mains, but severe interference with consumers occurs making the method unusable
Solution Approach 1:
The patent employs periodic measurement triggers synchronized with AC voltage zero-crossing points instead of continuous marking. This periodic approach limits interference to brief measurement intervals while maintaining cable connectivity, thus preserving productivity without causing severe consumer interference
Solution Approach 2:
The patent applies partial marking only at specific zero-crossing points of the AC waveform rather than continuous marking. This partial action provides sufficient directional information for fault location while minimizing interference with connected consumers, making the method practically usable
3Loss of time
If AC voltage is used for fault location measurement, then cable disconnection is avoided, but directional information is lost due to constantly changing voltage sign
Solution Approach 1:
The patent uses feedback from the AC voltage phase and zero-crossing detection to determine measurement timing. By triggering measurements at specific phase points and analyzing the polarity of step voltage relative to the AC cycle, the system recovers directional information that would otherwise be lost in continuous AC voltage
Solution Approach 2:
The patent performs preliminary identification of AC voltage zero-crossing points and establishes measurement trigger points before conducting fault location measurements. This preliminary action enables the system to capture directional information at appropriate moments in the AC cycle, preserving both continuity and directional accuracy
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 precise location of ground faults with reduced interference, allowing continuous operation of power supply networks and minimizing disturbances to consumers, as only slight modifications to the AC voltage are necessary for fault detection.
Implementation Method 1
an application device 2 tensioned to the cable 1, in particular designed as a mains fuse
Implementation Method 2
A direct current flows through the cable, which exits into the surrounding soil at the point of the earth fault and flows out in all directions. In this case, the ground at the ground fault point is subjected to the impact voltage and this voltage drops from there with increasing distance.
Implementation Method 3
The result is an AC voltage that is continuously deformed by the markings, which is difficult to use except for the present measurement purpose and causes severe interference with consumers.
Data Source
Figure 1
AI summary
The invention relates to a device for locating an earth fault (5) on a power supply cable (1) surrounded by a conductive medium by step voltage measurement at an accessible surface (4) of the medium, comprising a unit (2) for applying a voltage (9) of specific polarity to the cable (1) and a unit (8) for evaluating the step voltage. The unit (8) determines which of two tapping points (A, B) of the evaluating unit lies closer to the earth fault (5), the voltage being applied being an alternating voltage (9), the specific polarity of which is marked. The device is characterised in that at least one individual half-wave (11) or a group of half-waves of the specific polarity is marked by a deformation which is followed by a sequence of unmarked half-waves of the same polarity, wherein the evaluating device (8) is designed to determine a step voltage signal as the time curve (9) of the step voltage and to recognise individual marked half-waves (11) therein and to determine the polarity thereof.