Fault Distance Calculation Using Residual Voltage and Zero-Sequence Current
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Solution Overview
Problem
Existing methods for determining the distance to a phase-to-earth fault in three-phase electric networks require all phase-to-earth voltages and currents, which are not always readily available, and often necessitate additional measuring arrangements, and rely on secure faulted phase identification.
Innovation Solution
The method uses changes in residual voltage and zero-sequence current values to approximate the voltage change in the faulty phase, eliminating the need for all phase-to-earth voltage and current measurements, and models the zero-sequence circuit of the electric network to calculate fault distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If all phase-to-earth voltages and currents are used for fault distance calculation, then measurement precision is improved, but device complexity increases due to additional measuring arrangements
Solution Approach 1:
The patent extracts only the necessary measurement quantities (residual voltage and zero-sequence current) from the complete set of phase measurements, eliminating the need to measure all phase-to-earth voltages and currents. This extraction principle reduces device complexity while maintaining sufficient measurement precision for fault distance calculation.
Solution Approach 2:
The patent makes the protection device self-sufficient by utilizing measurement quantities (residual voltage and zero-sequence current) that are already available in the system, eliminating the need for additional dedicated measuring arrangements. This multi-functionality approach allows existing measurements to serve multiple purposes.
2Reliability
If all phase-to-earth voltages and currents are measured, then reliability of fault distance calculation is improved, but ease of operation deteriorates due to requirement of additional measuring arrangements
Solution Approach 1:
The protection device serves itself by utilizing measurement quantities (residual voltage and zero-sequence current) that are already available in the system without requiring additional external measuring arrangements. This self-service principle improves ease of operation while maintaining calculation reliability.
3Measurement precision
If phase voltages are used in fault distance calculation, then measurement precision is improved, but device complexity increases due to requirement of secure faulted phase identification procedure
Solution Approach 1:
The patent extracts the fault distance calculation from dependence on faulted phase identification by using residual voltage and zero-sequence current measurements. This extraction eliminates the need for complex faulted phase identification procedures while maintaining sufficient measurement precision through the inherent properties of residual and zero-sequence quantities.
Data Source
Figure 1~2
AI summary
Method and apparatus for determining a distance to a phase-to-earth fault on a three-phase electric line of an electric network, the apparatus comprising means (40) for determining, during a phase-to-earth fault (F) on the three-phase electric line (30), values of a residual voltage of the electric network and a zero-sequence current of the electric line at a measuring point (40) when a neutral to earth admittance of the electric network outside the electric line has a first value and when the neutral to earth admittance of the electric network outside the electric line has a second value different from the first value; and means (40) for determining the distance to the phase-to-earth fault (F) from the measuring point (40) on the basis of the determined residual voltage and zero-sequence current values.