Current Differential Protection Fault Identification via Adaptive Operate Value
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Solution Overview
Problem
Current differential protection methods face challenges in achieving a balance between sensitivity, speed, and reliability, particularly under heavy load conditions and CT saturation, leading to potential mal-trips and difficulties in distinguishing between internal and external faults.
Innovation Solution
A method that calculates fault component current vectors and uses a control factor related to the phase angle to differentiate between internal and external faults by comparing an operate value with a restrain value, allowing for improved sensitivity and reliability through adaptive operate characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the threshold is lowered to improve sensitivity and speed for internal fault identification, then the sensitivity and speed improve, but the reliability for external fault identification deteriorates
Solution Approach 1:
The patent applies dynamics by making the protection criterion adaptive rather than fixed. It dynamically adjusts the operate value calculation based on load current magnitude and power factor, switching between different calculation modes (full component based vs. fault component based) to optimize performance for different operating conditions, thereby simultaneously improving sensitivity and maintaining reliability
Solution Approach 2:
The patent changes parameters by introducing adaptive threshold adjustment based on load conditions. It modifies the operate value calculation parameters according to the measured load current and power factor, using different formulas for different operating regions, which allows the protection to maintain high sensitivity for internal faults while preventing mal-trip for external faults
2Reliability
If the threshold is raised to improve reliability for external fault identification, then the reliability improves, but the sensitivity and speed for internal fault identification deteriorate
Solution Approach 1:
The protection system dynamically selects different calculation approaches based on operating conditions. Under heavy load conditions, it switches to fault component based calculation with adaptive thresholds that ensure high reliability for external faults while maintaining sufficient sensitivity for internal faults through condition-based activation
3Measurement precision
If fault component based differential protection is used to improve sensitivity and speed under heavy load and high resistance fault conditions, then sensitivity and speed improve, but the reliability problem of CT saturation is not solved
Solution Approach 1:
The patent segments the protection criterion into multiple modes: full component based mode for normal conditions and fault component based mode for heavy load conditions. This segmentation allows each mode to be optimized for its specific operating range, with the fault component mode providing high sensitivity under heavy load while the overall system maintains reliability through selective activation
Solution Approach 2:
The patent changes the calculation parameters adaptively based on load conditions. It monitors load current magnitude and power factor, and switches between different operate value calculation formulas, thereby maintaining high sensitivity for internal faults under various conditions while preventing mal-trip for external faults with CT saturation
Data Source
AI summary
The present invention discloses a method for identifying the fault by current differential protection and a device thereof. The method comprises: measuring the full component currents of the two terminals of a two-terminal line system and calculating the corresponding fault component current vectors; obtaining an operate value by calculating a first difference between an absolute value of the sum of the fault component current vectors and Iset1; obtaining a restrain value by multiplying a second difference with a control factor, in which the second difference is calculated between the maximum of the absolute values of the fault component currents and Iset2 or between the absolute value of the difference of said fault component currents and Iset2; and identifying a fault as an external one or internal one by comparing the operate value with the restrain value. The solutions of the present invention achieve better reliability, sensitivity and faster speed than existing products.