Master-Slave Fiber Optic Current Sensors for Differential Protection
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Solution Overview
Problem
Current differential protection systems in electrical power transmission rely on conventional current transformers, which are sensitive to power swings and load changes, and lack efficient remote monitoring capabilities for fault detection and location.
Innovation Solution
A master-slave optical current sensor system is introduced, where the slave sensor is periodically recalibrated based on the master's output, allowing for remote operation and improved accuracy in differential current measurement, enabling health monitoring and fault location, optionally with voltage sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current transformers are used in differential protection systems, then current measurement can be achieved, but the system becomes sensitive to power swings and load changes
Solution Approach 1:
The patent replaces conventional current transformers (electromagnetic/mechanical system) with fiber optic current sensors that operate on optical principles (Faraday effect). This substitution eliminates the sensitivity to power swings and load changes that plagues electromagnetic CTs, as the optical sensing mechanism is inherently immune to these electrical disturbances while maintaining measurement reliability
2Ease of operation
If fiber optic current sensors are used for remote current sensing, then remote operation capability is improved, but measurement accuracy deteriorates due to drift between sensors
Solution Approach 1:
The patent implements a master-slave configuration where the master sensor serves as a reference and the slave sensor's measurements are continuously compared against it. A feedback mechanism recalibrates the slave sensor based on the master's output, compensating for drift and maintaining measurement accuracy across remote locations without sacrificing the remote operation capability
Solution Approach 2:
The system dynamically adjusts the slave sensor's measurement parameters (scaling factors, offset values) based on continuous comparison with the master sensor. This parameter adaptation allows the remote slave sensor to maintain accuracy despite environmental variations and drift, while preserving its remote operational advantage
3Measurement precision
If individual fiber optic current sensors are precisely calibrated, then measurement accuracy is improved, but the complexity and cost of calibration increases
Solution Approach 1:
The slave sensor performs self-calibration by continuously comparing its measurements with the master sensor and automatically adjusting its output parameters. This self-service mechanism eliminates the need for complex external calibration procedures for each individual sensor, reducing calibration complexity while maintaining measurement accuracy through continuous adaptive adjustment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system enhances the accuracy and reliability of differential current measurements, reduces the need for precise calibration of individual sensors, and allows for remote operation, effectively addressing the limitations of conventional systems by providing robust fault detection and location capabilities.
Implementation Method 1
fiber optic current sensors operate based on the Faraday effect. Current flowing in a wire induces a magnetic field which, through the Faraday effect, rotates the plane of polarization of the light traveling in the optical fiber wound around the current carrying wire
Data Source
AI summary
A master-slave current sensor system for measuring, for example, differential current on a transmission line is described. The slave current sensor can be periodically recalibrated (or have a compensation value re-calculated) based on the master sensor's average output, and the slave sensor can be unpowered and remote from an electronics box which receives its measurements. Health monitoring and fault location can also be performed using the master-slave optical current sensor system, optionally in conjunction with one or more voltage sensors.