Line Protection Using Corrected Current After Circuit Breaker Opening

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Solution Overview

Problem

Current line protection systems are limited in sensitivity due to decaying resonant currents caused by capacitive reactive current compensation, leading to suboptimal performance in protective device functions such as switch failure protection.

Innovation Solution

A method that calculates the current at the circuit breaker by subtracting the compensating current from the measured current using voltage measurements, allowing for sensitive threshold setting and improved protective device sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a current transformer is installed on the line side of the choke to measure current, then the protective device can detect circuit breaker status, but the decaying resonant current after circuit breaker opens causes false measurements and reduces protection sensitivity

Engineering Contradiction:

Improvecircuit breaker status detectionVSAvoidcurrent measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces a voltage transformer as an intermediary measuring device on the load side of the circuit breaker. Instead of directly measuring current through the circuit breaker (which is contaminated by resonant current), the system measures voltage and calculates the load current indirectly. This intermediary measurement approach eliminates the harmful resonant current interference while maintaining reliable circuit breaker status detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct current measurement (electrical measurement through current transformer) with voltage measurement and mathematical calculation. By substituting the direct current sensing method with a voltage-based calculation approach, the system avoids the resonant current interference that plagues direct current measurements during circuit breaker operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a high minimum current threshold is set for open circuit breaker detection to avoid false triggers from resonant current, then false triggers are reduced, but the sensitivity of protective device functions is significantly reduced

Engineering Contradiction:

Improvefalse trigger reductionVSAvoidprotection sensitivity

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The voltage transformer serves as an intermediary that provides clean measurement data free from resonant current contamination. By measuring voltage on the load side and calculating current indirectly, the system obtains accurate current values even during circuit breaker operation, enabling both high sensitivity and low false trigger rates simultaneously.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the problematic resonant current phenomenon into a non-issue by changing the measurement location to the load side of the circuit breaker. The resonant current that would normally cause false triggers is isolated from the measurement point, allowing the use of low current thresholds for high-sensitivity protection without risking false alarms.

Inventive Principle:

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

3Speed

If current is measured directly through the circuit breaker to monitor line status, then real-time monitoring is achieved, but the capacitive reactive current from the choke creates resonant oscillations that distort measurements

Engineering Contradiction:

Improvereal-time monitoring speedVSAvoidcurrent measurement accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The system uses voltage measurement as an intermediary step between the circuit breaker and the protection logic. By measuring voltage and calculating current through mathematical operations rather than direct current sensing, the system maintains real-time monitoring capability while eliminating the measurement distortion caused by resonant oscillations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent substitutes direct current measurement with a voltage measurement and calculation system. This substitution replaces the problematic direct electrical connection through the circuit breaker with an indirect measurement approach that uses voltage sensing and mathematical computation to derive current values free from resonant interference.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP3916939B1Method for line protection and protection arrangement

Publication Date: 2023.10.11 SIEMENS AG

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AI summary

The present invention relates to a method for line protection in which a choke device (7, 8, 27-30) for reactive power compensation is provided on an electrical line (2, L1, L2, L3), and a resonant current (ICT) is measured on the line side of the choke device (7, 8, 27-30) by means of a first measuring device (9, 24-26) after opening a circuit breaker (5), characterized in that a voltage is measured by means of a second measuring device (10, 31-33) after opening the circuit breaker (5), and that a current (ISH) in the choke device is calculated from the measured voltage by means of an evaluation device, and the calculated current (ISH) is subtracted from the measured resonant current (ICT) by means of the evaluation device to obtain a corrected current (ICB). Furthermore, the present invention relates to a protective arrangement.