Frequency Interpolation for Disturbance Evaluation
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Solution Overview
Problem
Existing disturbance evaluation systems face challenges in accurately predicting fault currents and calculating network impedance, especially when dealing with small disturbances, due to inaccuracies in frequency assessment which are critical for representing phase changes in voltage and current signals.
Innovation Solution
An apparatus with measuring means for obtaining signal frequencies before and after a disturbance, using interpolation to calculate frequency trends across the disturbance interval, excluding the influence of the disturbance transient, by employing a delay line with access points at both ends to derive and combine frequency measures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency assessment includes the disturbance transient period, then more data points are available for frequency calculation, but the accuracy of frequency assessment deteriorates due to the influence of transient disturbances
Solution Approach 1:
The frequency assessment process is segmented into three distinct time periods: before disturbance, during disturbance (excluded), and after disturbance. By dividing the analysis window and excluding the transient period, the system obtains frequency measurements from stable periods only, thereby maintaining high accuracy while still having sufficient data points from the pre and post disturbance periods for reliable frequency calculation.
2Measurement precision
If the disturbance transient is excluded from frequency assessment, then frequency accuracy improves, but the period of interest for disturbance analysis is reduced
Solution Approach 1:
The system performs preliminary frequency assessment using data from the period before the disturbance occurs. This preliminary action establishes a baseline frequency that can be projected forward, allowing the system to maintain accurate frequency knowledge even during the excluded transient period, thereby effectively extending the useful analysis period without compromising accuracy.
3Difficulty of detecting and measuring
If projection of voltage and current signals is used to extract difference information, then disturbance analysis capability is enhanced, but frequency assessment accuracy becomes more critical and harder to maintain
Solution Approach 1:
The patent introduces an intermediary approach by using frequency assessment from stable periods (before and after disturbance) as a mediator to represent the frequency during the disturbance period. This intermediary frequency value, obtained from unaffected periods, enables the projection and comparison techniques to work accurately without being corrupted by transient frequency variations during the disturbance itself.
Data Source
Figure 1~2
Figure 3
AI summary
Apparatus (1) for use in disturbance evaluation systems based on disturbance extraction, which apparatus (1) comprises measuring means for obtaining signal frequency both before (4) and after a disturbance (3) in an electricity network but excluding use of the disturbance transient itself, and interpolation means (5) for interpolating frequency across the disturbance interval to reflect the underlying frequency trend (9) uninfluenced by the disturbance transient. The apparatus (1) may include: (i) at least one delay means (2) for receiving at least one analogue or digital signal (6) from the electricity network; (ii) at least one first access point (P) at a first part of the delay means (2); (iii) at least one second access point (Q) at a second part of the delay means (2), and the apparatus (1) being such that: (iv) the measuring means comprises: (a) a first frequency derivation means (3) for processing a set of access point outputs from the first access point and providing at least one measure of frequency (7) after the disturbance; and (b) a second frequency derivation means (4) for processing a set of access point outputs from the second access point or a delayed output means, for providing at least one measure of frequency (8) before the disturbance; and the interpolation means (5) receives the measure of frequency (7) after the disturbance and the measure of frequency (8) before the disturbance, and provides a measure of frequency (9) as a function of time over a period of interest, which comprises the disturbance interval and either side of the disturbance interval.