Fault Level Estimation Using Segmented Impedance Measurement
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Solution Overview
Problem
Existing methods for estimating fault levels in electrical power supply networks struggle to accurately account for motor contributions, both upstream and downstream of a measurement point, due to the difficulty in distinguishing between motor and resistive load changes, leading to uncertainties in fault current assessments.
Innovation Solution
The apparatus and method involve calculating upstream and downstream impedances using changes in electrical power supply, with downstream calculator means determining dynamic motor contributions by measuring static and actual impedances, and combining these with upstream impedance to estimate fault levels, thereby addressing the motor contribution uncertainty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motor contribution is included in fault level estimation, then accuracy of fault current assessment is improved, but device complexity increases due to difficulty in distinguishing motor from resistive load changes
Solution Approach 1:
The patent divides the network impedance measurement into two separate measurements: upstream impedance (from power source to measurement point) and downstream impedance (from measurement point to load). By segmenting the measurement, the system can separately identify motor contributions downstream without being confused by upstream variations, thus improving accuracy while managing complexity through structured separation of measurement functions
Solution Approach 2:
The patent introduces a reference impedance measurement taken when motors are known to be off, serving as an intermediary baseline. This reference measurement acts as a mediator that allows the system to distinguish between resistive load changes and motor contributions by comparing against the known baseline, thereby improving measurement precision without requiring complex real-time motor identification algorithms
2Reliability
If natural disturbances are used to measure impedance changes, then fault level estimation can be performed without deliberate faults, but measurement precision deteriorates due to inability to distinguish motor from resistive load changes
Solution Approach 1:
The patent performs preliminary impedance measurements during periods when motors are known to be off, establishing baseline upstream and downstream impedance values before normal operation begins. This preliminary action allows the system to capture accurate reference data without the complicating factor of motor contributions, ensuring measurement precision is maintained while still using natural disturbances during operation
Solution Approach 2:
The patent dynamically adjusts the measurement strategy by taking impedance measurements at different operational states (motors off, motors on). By transitioning between these dynamic states and comparing measurements, the system can isolate motor contributions from resistive load changes, maintaining measurement precision while utilizing natural disturbances during normal operation
Data Source
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AI summary
Apparatus (16) for use in estimating a fault level in a network (2) providing an electric power supply to consumers, which apparatus (16) comprises: (i) upstream calculator means (18) for calculating upstream impedance by utilising changes which occur after and consequent upon changes in the electrical power supply due to consumer removal or supply of electricity to the network (2); and (ii) downstream calculator means (20) for: (a) calculating a static downstream impedance which is based on measurements before and/or after the time when the changes in the electrical power supply occur; (b) measuring the actual downstream impedance at the time when the changes in the electrical power supply occur; and (c) obtaining the difference between the calculated static downstream impedance and the actual downstream impedance.