Insulation Fault Location in Isolated AC Networks
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Solution Overview
Problem
Existing methods for detecting insulation faults in alternating voltage networks are inefficient, unreliable, and disruptive, as they require active feeding, are limited by network length, and struggle with high impedance faults due to the influence of capacitances and inductances in AC systems.
Innovation Solution
A circuit arrangement with a selection switch to connect feed conductors to ground potential and detection devices to measure current changes, using a computing unit to identify faulty branches by analyzing parasitic ground currents, which accounts for both ohmic and capacitive components, allowing for selective and accurate fault detection without disrupting the network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If systematic switching on and off of individual feeders is used to detect insulation faults, then fault detection capability is improved, but network availability deteriorates because feeders cannot supply loads during switching-off periods
Solution Approach 1:
The invention applies periodic action by using a selection switch to periodically connect different feeder conductors to earth potential in sequence, while detection devices continuously monitor current changes during these periodic switching operations. This allows fault detection without requiring complete feeder disconnection, maintaining network availability while enabling systematic fault identification through periodic earth connection of individual feeders.
2Measurement precision
If voltage modulation method is used to locate faulty feeder, then fault detection capability is improved, but network length limitation worsens because it requires active feeder which limits maximum network length
Solution Approach 1:
The invention substitutes the voltage modulation method with a direct current injection method. Instead of modulating voltage and relying on active feeder response, the system injects test currents through the selection switch and directly measures current changes with detection devices. This substitution eliminates the maximum network length limitation while maintaining accurate fault location capability.
3Measurement precision
If known AC fault detection methods are used, then fault detection is possible, but reliability worsens due to additional influences from capacitances and inductances in AC networks
Solution Approach 1:
The invention extracts and isolates the resistive component of the fault current from the total AC current by using a selection switch to connect feeders to earth potential and detection devices to measure current changes. This separation allows reliable fault detection by focusing only on the resistive fault current component, eliminating the interfering influences of capacitances and inductances that are inherent in AC networks.
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 cost-effective, selective, and reliable localization of insulation faults, preventing disruptions to consumers and allowing for the detection of small fault currents and high fault resistances, while being robust and accurate, without the need for additional feed means.
Implementation Method 1
the earth current also includes a variable component dependent on the parasitic line capacitances
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a circuit arrangement for locating insulation faults to earth in isolated AC networks up to 750V, in which the voltage of an AC voltage source (1) is applied to two feed conductors (E1, E2) of the AC network having at least two branches (AZ1, AZ2, ...AZn), comprising a selector switch (8) for selectively connecting the feed conductors (E1, E2) to earth potential and a detection device (7) assigned to each branch (8-1, ..., 8-n) to be checked for detecting a change in current in the branch, wherein a fault detection device (2) for detecting and evaluating network parameters is arranged between the AC voltage source (1) and the feed conductors (E1, E2), wherein the fault detection device (2) is configured to compare actual values of the network parameters with predefinable target values and thereby detects the faulty feed conductor (E1, E2).and upon the occurrence of a predefinable deviation from the target values, a control (5) for the selection switch (8) is switched from a standby state to an activated state, wherein the control (5) permits the connection of the faulty feed-in conductor (E1, E2) to earth potential only during the duration of the activated state, wherein the detection devices (7) are connected to a processing unit (12) to which the measurement results (S1, S2, S3, S4, Sz) detected by the detection devices (7) are supplied, wherein the processing unit (12) is configured to derive from the measurement results (S1, S2, S3, S4, Sz) at least the magnitude of the parasitic earth current (Ic1, Ic2, Ic3, Ic4, Icz) of the respective branch (8-1, ..., 8-n), and by detecting the change in at least the parasitic earth current (Ic1, Ic2, Ic3, Ic4, Icz) during the period of grounding of the faulty feed-in conductor (E1, E2) to identify the faulty branch (8-1, ..., 8-n).