Current Transformer Open Circuit Detection via Harmonic Analysis

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Solution Overview

Problem

Current transformer open circuit conditions are not adequately detected, leading to safety hazards, equipment damage, and unnecessary power system shutdowns due to incomplete monitoring and corrective actions in existing technologies.

Innovation Solution

A method involving voltage and current measurement on the secondary side of a current transformer, using voltmeters and ammeters connected to a controller that performs Fast Fourier Transform analysis to identify characteristic harmonic signatures indicative of an open circuit, allowing for immediate corrective actions such as alarms or system shutdowns.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a test plug is used to limit over voltage by switching on an electronic component in parallel with the main current path, then operator safety is improved, but the current continuity to protective relays is disrupted and waveform integrity is degraded

Engineering Contradiction:

Improveover voltage hazardVSAvoidcurrent continuity and waveform integrity

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent introduces an intermediary detection mechanism (voltage monitoring circuit with FFT analyzer) that indirectly detects open circuit conditions by analyzing harmonic content, rather than directly switching the main current path. This mediator approach allows safety monitoring without disrupting current continuity to protective relays.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the mechanical/electronic switching mechanism of prior art test plugs with a signal processing approach using Fast Fourier Transform analysis. Instead of physically switching components to limit voltage, the system uses digital signal processing to detect open circuit conditions through harmonic analysis, eliminating the need for current-disrupting switches.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If the test plug continuously monitors and switches to limit voltage, then operator safety is improved, but protective relays experience disturbances causing unnecessary power system shutdowns

Engineering Contradiction:

Improveunlimited over voltageVSAvoidpower system availability

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The patent implements a feedback mechanism where the voltage monitoring circuit continuously analyzes the secondary side voltage waveform, detects open circuit conditions through FFT harmonic analysis, and triggers appropriate responses. This feedback loop provides accurate detection without the disruptive on-off switching of prior art, preventing false disturbances to protective relays.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent uses periodic Fast Fourier Transform analysis of the voltage waveform to detect open circuit conditions. By continuously analyzing the harmonic content at regular intervals, the system can detect anomalies without requiring the discontinuous switching action of prior art test plugs, thereby maintaining power system availability.

Inventive Principle:

Principle #19Periodic action

3Measurement precision

If off-line testing is used to check current transformer health, then device status can be assessed, but the system is not monitored in real-time and safety risks persist during operation

Engineering Contradiction:

Improvecurrent transformer health assessmentVSAvoidreal-time safety monitoring

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements preliminary detection by continuously monitoring the secondary side voltage waveform for characteristic harmonic signatures of open circuit conditions. This preliminary action allows the system to detect potential safety issues in real-time during operation, rather than waiting for off-line testing after the fact.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent enables the current transformer system to self-monitor its own health status through the voltage monitoring circuit and FFT analyzer. The system automatically detects open circuit conditions by analyzing its own secondary side voltage waveform, eliminating the need for external off-line testing and providing continuous real-time safety monitoring.

Inventive Principle:

Principle #25Self-service

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

Enables reliable detection of open current transformers without disrupting the power system, ensuring operator safety and maintaining waveform integrity by initiating appropriate corrective actions based on harmonic analysis.

Implementation Method 1

Methodology Applied

Scientific EffectFast Fourier Transform:

Data Source

PatentUS9568535B2Methods for detecting an open current transformer

Publication Date: 2017.02.14 ABB RES LTD

AI summary

A method for detecting an open current transformer in an electrical power system includes measuring for a voltage value on a secondary side of a current transformer. The method continues with observing the voltage value for a predetermined waveform and initiating corrective action in the electrical power system upon detection of the predetermined waveform.