FOCT Offset Cancellation via Signal Normalization

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Solution Overview

Problem

Current current transducers, particularly those using iron core transformers and fiber-optic current transducers (FOCTs), face challenges in accurately measuring current due to distortions caused by hysteresis in iron cores and temperature-induced DC offsets in Faraday rotators, leading to inaccurate current estimation in high voltage transmission lines.

Innovation Solution

The implementation of a processing unit in FOCTs that normalizes and adjusts electrical signals from light signals to the same per unit basis, effectively removing offsets and non-symmetrical features, thereby enhancing the accuracy of current measurement by compensating for temperature variations and optical losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If iron core current transformers are used for current measurement, then current monitoring capability is provided, but significant signal distortions occur due to hysteresis effects

Engineering Contradiction:

Improvecurrent monitoring capabilityVSAvoidsignal accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent replaces iron core transformers with fiber-optic current transducers that use optical fields instead of magnetic fields for current measurement. The FOCT uses a light beam passing through a Faraday rotator and polarizer to measure current, eliminating the hysteresis effects inherent in iron core transformers while maintaining reliable current monitoring capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If fiber-optic current transducers are used for current measurement, then measurement accuracy is improved, but DC offsets are introduced due to temperature variations in the Faraday rotator

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidtemperature-induced DC offsets

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a feedback mechanism where the system measures the DC offset components in the X and Y signals, determines their magnitude, and then subtracts these offset values from the respective signals. This feedback loop continuously compensates for temperature-induced DC offsets, maintaining measurement accuracy despite environmental variations

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent converts the harmful DC offset effect into a measurable and correctable parameter. By identifying and quantifying the offset components, the system transforms the temperature-induced error into a known quantity that can be systematically removed through signal processing, thereby eliminating its harmful effect

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Productivity

If conventional FOCT signal processing is used, then current estimation is provided, but inaccurate results occur due to uncorrected DC offsets

Engineering Contradiction:

Improvecurrent estimation capabilityVSAvoidcurrent estimation accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by removing DC offsets from the X and Y signals before performing current estimation calculations. By preprocessing the signals to eliminate offset components prior to the estimation algorithm, the system ensures that subsequent current calculations are based on accurate, offset-free signal components

Inventive Principle:

Principle #10Preliminary action

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 approach provides more accurate current measurements by eliminating DC offsets and non-symmetrical distortions, enabling reliable detection of current transients and reducing noise immunity, thus improving the performance of current transducers in high voltage transmission line monitoring.

Implementation Method 1

FOCTs operate on the principle of Faraday rotation, which is a magneto-optical effect whereby a rotation of the plane of polarization of a light beam confined in a fiber-optic waveguide placed near the transmission line is observed in response to a magnetic field induced by the flow of current

Methodology Applied

Scientific EffectFaraday rotation: Faraday Effect

Implementation Method 2

the third fiber is a low birefringence fiber (LBF) that is wrapped around the transmission line

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS10473697B2Current transducer with offset cancellation

Publication Date: 2019.11.12 GE INFRASTRUCTURE TECH LLC

AI summary

There is provided a system for use with a fiber-optic current transducer. The system includes a processing unit configured to transduce a first light signal into a first electrical signal. The processing unit is further configured to transduce a second light signal into a second electrical signal. Furthermore, the processing unit is configured to remove offsets from the first electrical signal and the second electrical signal by forcing the first electrical signal and the second electrical signal to be on the same per unit basis.