Adaptive Pulse Test Current for Insulation Fault Localization
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Solution Overview
Problem
In widely branched unearthed power supply systems, high-impedance insulation faults and large system leakage capacitances lead to unreliable detection and localization of insulation faults due to interference from leakage currents, limiting the effectiveness of existing insulation fault location methods and requiring excessive test currents or system shutdowns.
Innovation Solution
The method involves generating a periodic locating current with adjustable pulse and pause durations, maintaining a maximum permissible amplitude, to eliminate disturbance variables and accurately detect differential currents, using measuring current transformers to track residual currents and determine settling times, ensuring reliable fault localization while adhering to safety limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a test current is injected to detect insulation faults in widely branched ungrounded power supply systems, then fault detection capability is improved, but leakage currents from large network capacitances create interference that reduces measurement reliability
Solution Approach 1:
The patent applies periodic test current pulses with alternating polarity (positive and negative half-cycles) to excite the network. By using periodic action, the capacitive leakage currents become time-dependent and can be distinguished from the steady-state test current through time-domain analysis, resolving the measurement interference issue.
Solution Approach 2:
The patent performs preliminary determination of capacitive leakage currents during the transient phase before the steady-state measurement is taken. This preliminary action allows the system to compensate for or eliminate the interference from large network capacitances before the actual fault current measurement, improving measurement precision.
2Measurement precision
If the test current amplitude is increased to improve detection of high-resistance insulation faults, then detection sensitivity is improved, but safety limits for personnel and equipment protection are exceeded
Solution Approach 1:
The patent uses periodic test current pulses with alternating polarity instead of continuous high-amplitude current. The pulsed nature allows the system to achieve sufficient detection sensitivity through cumulative effect while keeping the peak amplitude within safety limits, thus resolving the contradiction between detection sensitivity and safety.
Solution Approach 2:
The patent changes the temporal parameters of the test current (pulse width, frequency, duty cycle) rather than simply increasing amplitude. By optimizing these parameters, the system achieves high detection sensitivity for high-resistance faults while maintaining peak current levels within safe operational limits for personnel and equipment.
3Reliability
If a test current is injected into the power supply system to locate insulation faults, then fault localization capability is improved, but system operation is interrupted requiring shutdowns
Solution Approach 1:
The patent employs periodic test current injection that can be performed during normal system operation without requiring shutdown. The periodic nature allows the test to be integrated into the operational cycle, enabling fault localization while maintaining system availability and productivity.
Solution Approach 2:
The patent enables continuous monitoring and fault detection capability by using test currents that can be injected during normal operation. This maintains the continuity of useful action (power supply to consumers) while simultaneously performing fault localization, eliminating the need for system shutdowns.
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
This approach enables efficient and technically reliable insulation fault localization in terms of time and cost, maintaining personal and system protection by eliminating dynamic interference components and avoiding incorrect measurements, even with large system leakage capacitances.
Implementation Method 1
The test current generator produces a test current and injects it at a central point into the ungrounded power supply system between one or more live conductors and earth (injected test current). This creates a closed circuit in which the test current flows from the test current generator through the live conductors, the insulation fault, and back to the test current generator via an earth connection.
Implementation Method 2
The fault location is determined by detecting the test current in the ungrounded power supply system using the insulation fault locator and its connected current transformers. Each section of the line being monitored is permanently assigned a current transformer.
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for locating insulation faults and an insulation fault detection device for an ungrounded power supply system. The basic concept of the present invention is based on adaptively adjusting the pulse duration of a test current, while maintaining a predetermined maximum permissible test current amplitude, such that all disturbances in a detected differential current, in particular leakage currents resulting from large network leakage capacitances, are eliminated. If a test of the magnitude of the final value of the differential current reveals that a test current limit is exceeded, this exceedance serves as an indicator that the relevant line section is located within the fault current circuit.