Circuit Breaker Reclosing Using Shunt Reactor Current Derivative
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Solution Overview
Problem
Conventional methods for controlled reclosing of circuit breakers in high or medium voltage power systems face challenges due to inaccurate measurements of line voltage after tripping, which can lead to high overvoltages and stress on transmission line insulation, especially when zero crossings of reactor current do not coincide with zero crossings of source voltage and line frequency is not constant.
Innovation Solution
A method and device that calculate the line voltage from the time derivative of a current through a shunt reactor, using a current transformer connected in series with the shunt reactor, allowing for controlled reclosing based on the difference between source voltage and the derived line voltage, without requiring coincident zero crossings or constant line frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional voltage transformers are used to measure line voltage after CB tripping, then the measurement system is simple, but the measurement precision deteriorates due to frequency deviations from nominal power frequency
Solution Approach 1:
The patent replaces conventional voltage transformers (electromagnetic measurement devices) with a computational approach using current transformer measurements and mathematical differentiation. The line voltage is calculated from the time derivative of shunt reactor current rather than directly measured, substituting physical electromagnetic transformation with mathematical processing to achieve frequency-independent measurement precision
Solution Approach 2:
The patent changes the measurement parameter from direct voltage measurement to current derivative measurement. By measuring current through the shunt reactor and calculating its time derivative, the system obtains line voltage information that remains accurate across varying frequencies, unlike conventional voltage transformers tuned to nominal frequency
2Reliability
If controlled reclosing is performed without accurate line voltage measurement, then the reclosing operation is simpler, but the reliability deteriorates due to high overvoltages and insulation stress
Solution Approach 1:
The patent replaces direct voltage measurement with computational derivation from current measurements. By using the relationship between shunt reactor current and line voltage through mathematical differentiation, the system achieves reliable controlled reclosing decisions without the frequency limitations of conventional voltage transformers
Solution Approach 2:
The patent introduces the shunt reactor current as an intermediary measurement quantity. Instead of measuring line voltage directly, the system measures current through the shunt reactor and uses its time derivative as a proxy for line voltage, providing accurate information for reclosing control across all frequency conditions
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 and reliable controlled reclosing of circuit breakers, reducing the risk of high overvoltages and improving insulation stress on transmission lines by using the time derivative of the shunt reactor current to estimate line voltage, even at varying frequencies.
Implementation Method 1
a current transformer connected in series with the shunt reactor
Implementation Method 2
a shunt reactor coupled to the transmission line
Data Source
AI summary
A power system comprises a power source, a transmission line coupled to the power source through a circuit breaker, a shunt reactor coupled to the transmission line, and a current transformer connected in series with the shunt reactor. A method for controlling the circuit breaker of the power system comprises processing an output signal of the current transformer to obtain the voltage on the transmission line by determining a time derivative of a current sensed by the current transformer. The method further comprises performing, by at least one control or protection device, a control or protection operation (e.g., auto-reclosing) based on the determined time derivative of the current sensed by the current transformer.