Impedance Vector Rotation for Distance Protection
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Solution Overview
Problem
Distance protection devices incorrectly detect faults during pendulum movements in electrical networks, leading to unnecessary line disconnections that exacerbate grid instability, as they cannot differentiate between pendulum movements and actual short circuits without significant time delays.
Innovation Solution
A method that classifies impedance movements by forming impedance change vectors and monitoring their direction and rotation, generating a classification signal to unlock distance protection devices before the typical reversal point dwell phase, allowing for early detection of short circuits within pendulum movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distance protection devices block during pendulum movements to avoid false tripping, then reliability improves, but detection speed of actual short circuits deteriorates due to the reversal point dwell phase delay
Solution Approach 1:
The patent segments the reversal point evaluation into two independent parts: (1) checking whether directed continuous impedance movement resumes within a predetermined time period, and (2) evaluating the rotation angle of impedance change vectors. This segmentation allows the system to independently assess each criterion and make faster decisions about unlocking the distance protection device, reducing the overall detection delay while maintaining reliability.
Solution Approach 2:
The patent applies partial action by checking only the rotation angle of impedance change vectors in the area of the reversal point, rather than requiring the full thirty mains periods to elapse. By monitoring the rotation angle (comparing angles before and after the reversal point), the system can partially evaluate the pendulum movement characteristics and make an earlier decision to unlock the protection device if a short circuit is detected, thus reducing detection delay while maintaining sufficient reliability.
2Measurement precision
If distance protection devices wait for the full reversal point dwell phase to ensure accurate classification, then measurement precision improves, but productivity deteriorates due to delayed fault response
Solution Approach 1:
The patent performs preliminary evaluation of the impedance movement characteristics by checking whether directed continuous movement resumes within a predetermined time period and by evaluating the rotation angle of impedance change vectors in the reversal point area. This preliminary action allows the system to make an early decision about the presence of a short circuit before the full thirty mains periods elapse, thus improving productivity (fault detection speed) while maintaining measurement precision through the dual-criterion evaluation approach.
3Loss of time
If the system monitors impedance change vectors and their rotation to enable early detection, then detection speed improves, but device complexity increases
Solution Approach 1:
The patent extracts and focuses specifically on the rotation angle of impedance change vectors in the area of the reversal point as the key indicator for early fault detection. By taking out this specific parameter (rotation angle) from the overall impedance analysis and making it the primary criterion for early decision-making, the system achieves faster detection speed while limiting the complexity increase to only the necessary vector rotation calculation, rather than requiring complex analysis of the entire impedance trajectory.
Data Source
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AI summary
The invention relates, inter alia, to a method for generating a classification signal (Q) that classifies an electrical impedance. According to the invention, the temporal evolution of the impedance is measured by generating impedance values (Z, Z0-Z6). Impedance change vectors (dZ1-dZ5) are generated with temporally successive impedance values (Z, Z0-Z6), the direction of which describes the movement of the impedance in the complex impedance plane and the length of which describes the magnitude of the respective impedance change. Based on the impedance values (Z, Z0-Z6) and/or the impedance change vectors (dZ1-dZ5), it is checked whether the impedance exhibits a directed continuous impedance movement according to at least one predetermined movement criterion. In the case of a previously detecteddirected continuous impedance motion and, in the case of a subsequent detected change in the direction of the impedance motion, the reaching of a reversal point (U) is inferred, and the rotation of the impedance change vectors (dZ1-dZ5) in the region of the reversal point (U) is monitored by forming a rotation angle measurement (ϕs), and a classification signal (Q) indicating an error (F) is generated if the impedance change vectors (dZ1-dZ5) in the region of the reversal point (U) have rotated by a predetermined maximum rotation angle or more than the predetermined maximum rotation angle.