Faraday Optical Current Transformer Cascade for Differential Protection

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Solution Overview

Problem

The introduction of optical differential protection into transformer protection faces challenges due to unequal amplitudes and phase differences in line currents on both sides of the protected object, caused by transformation ratios and connection configurations, leading to excessive differential currents and potential false tripping.

Innovation Solution

An optical computation method and system based on the Faraday magneto-optical rotation effect are employed, which includes a cascaded optical computation approach using three optical current transformers connected in series. This method calculates differential currents by performing optical addition and subtraction operations on the Faraday rotation angles, effectively addressing the phase and amplitude mismatches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If optical differential protection is directly introduced into transformer protection, then fast response speed and full waveform information utilization are improved, but false tripping risk increases due to unequal amplitudes and phase differences in line currents

Engineering Contradiction:

Improveresponse speedVSAvoidfalse tripping risk

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the parameters of the optical current transformers by introducing different magnification factors (k1, k2, k3) to compensate for the unequal amplitudes and phase differences caused by transformer connection groups. This allows the system to maintain fast optical-domain response while achieving accurate differential current calculation that prevents false tripping.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces an intermediary computational layer that processes optical signals through a system of equations involving Faraday rotation angles and magnification factors. This intermediary processing step reconciles the phase and amplitude differences between high-voltage and low-voltage side currents, enabling reliable transformer protection without sacrificing the speed advantages of optical differential protection.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If traditional differential protection based on power frequency quantity is used, then phase and amplitude equality assumptions hold, but response speed decreases due to digital filtering window processing

Engineering Contradiction:

Improvephase and amplitude equalityVSAvoidresponse speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent replaces the traditional mechanical/electrical signal processing system with an optical computation system. By using optical current transformers and Faraday rotation effects, the system performs differential current calculation in the optical domain without requiring digital filtering windows, thereby achieving both fast response speed and accurate phase/amplitude handling through optical-domain mathematical operations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If transformation ratio and connection group effects are compensated, then measurement precision improves, but device complexity increases due to cascaded optical computation

Engineering Contradiction:

Improvedifferential current measurement accuracyVSAvoidoptical computation system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges multiple optical current transformers with different magnification factors into a cascaded optical computation system. By combining the optical signals from three optical current transformers and processing them through a unified mathematical model involving Faraday rotation angles, the system achieves precise differential current measurement while keeping the overall device structure integrated and manageable.

Inventive Principle:

Principle #5Merging (Combining)

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

The proposed solution accurately measures differential currents in transformer protection, reducing the risk of false tripping and enhancing the reliability of optical differential protection systems by accounting for transformation ratios and connection configurations.

Implementation Method 1

optical calculation method and system for relay protection based on the Faraday magneto-optical rotation effect

Methodology Applied

Scientific EffectFaraday magneto-optical rotation effect: Faraday Effect

Data Source

PatentUS20250052792A1Method and system for optical calculation in relay protection based on the faraday magneto-optical rotation effect

Publication Date: 2025.02.13 HARBIN INST OF TECH

AI summary

Optical calculation method and system for relay protection based on Faraday magneto-optical rotation effect are provided. A cascaded optical computing approach is employed, where three optical current transformers are connected in series on a single optical path. Final output optical signal represented as a cascaded multiplication of outputs of three optical current transformers, carries a Faraday rotation angle containing differential current information. Differential current required for protection is computed by modulation ratio which is calculated by use of a carrier and modulation wave signals of the output optical signal detecting by filtering circuit from the third optical current transformer.