Cumulative Phasor Sum for Fault Direction Determination
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Solution Overview
Problem
Existing fault direction determination methods in power systems face instability due to non-constant amplitudes and frequencies of voltages and currents during faults, leading to unreliable directional decisions and potential loss of selectivity in power system protection.
Innovation Solution
The method involves using a cumulative phasor sum or quotient of cumulative phasor sums of electric phasor quantities at different time instants to stabilize the directional phasor quantities, allowing for more accurate and dependable fault direction determination even with distorted signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional phasor quantities are used for fault direction determination, then the method is simple and straightforward, but the results become unstable and unreliable during faults with non-constant amplitudes and frequencies
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the cumulative phasor sum of voltage and current before the fault occurs. This pre-computed cumulative sum serves as a stable reference that can be directly compared with post-fault measurements, eliminating the need for complex real-time calculations during the fault condition when signals are distorted.
Solution Approach 2:
The patent changes the parameter from instantaneous phasor values to cumulative phasor sums. By integrating the phasor quantities over time before the fault, the system transforms the measurement parameter into a form that is less sensitive to amplitude and frequency variations during the fault, thereby improving reliability without significantly increasing complexity.
2Speed
If instantaneous phasor values are used for directional determination, then the response is immediate, but the measurements are highly sensitive to signal distortions and amplitude variations during faults
Solution Approach 1:
The system performs the cumulative summation of phasors in advance, before the fault distorts the signals. This pre-computed reference value captures the normal operating state and can be immediately compared with post-fault measurements, achieving both fast response and high precision by avoiding real-time integration during the fault condition.
Solution Approach 2:
The patent introduces a dynamic approach by using the cumulative phasor sum that adapts to changing operating conditions while maintaining stability. The cumulative sum naturally filters out high-frequency noise and transient disturbances, providing a robust reference that remains valid even when signal characteristics change during the fault.
Data Source
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AI summary
A method and an apparatus for determining a direction of a fault in a three-phase electric network, the apparatus comprising means (10) for determining a value for a directional phasor quantity at a measuring point in the three-phase electric network after a fault has been detected in the three-phase electric network, and means (10) for comparing the determined value for the directional phasor quantity with a directional operation characteristic to determine the direction of the fault from the measuring point, wherein the means (10) for determining the value for the directional phasor quantity comprises means for forming a cumulative phasor sum of at least two values, determined at different instants of time, of an electric phasor quantity at the measuring point; and means for setting the cumulative phasor sum as the value for the directional phasor quantity.