Differential Protection Device Fault Segmentation
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Solution Overview
Problem
Current differential protection methods in electrical power systems face challenges in distinguishing between primary and secondary faults within current transformer circuits, leading to potential unnecessary tripping of primary transmission lines and circuit breaker misoperation.
Innovation Solution
A method employing current differential protection devices at both ends of a protected object, comparing changes in measured values to determine the type of fault, allowing for independent detection of faults within current transformer circuits and avoiding circuit mixing, thereby differentiating between primary and secondary faults and issuing tripping commands only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If local measurements from current transformers are used to detect faults, then fault detection capability is provided, but it becomes difficult to determine whether the fault originates in the protection equipment or in the reference protection equipment
Solution Approach 1:
The fault detection function is segmented into independent protection devices at each end of the protected object. Each device independently monitors its own current transformer circuits and compares measurements with the other end, allowing independent fault detection without circuit mixing. This segmentation enables clear identification of whether a fault occurs in local or remote current transformer circuits.
Solution Approach 2:
A communication channel acts as an intermediary between protection devices at different ends, transmitting measured values and comparison results. This intermediary enables each device to obtain remote measurements without direct circuit connection, resolving the ambiguity of fault origin by allowing independent analysis of local versus remote measurement anomalies.
2Adaptability or versatility
If circuit mixing of two protection equipment is used to obtain reference values, then differential protection functionality is achieved, but it becomes difficult to determine whether a fault is a primary network fault or a secondary network fault
Solution Approach 1:
The protection system is divided into independent protection devices, each with its own current transformer circuits. By comparing measurements from independently monitored circuits at both ends, the system can reliably determine whether a fault is primary (affecting both ends) or secondary (affecting only one end's local circuits), eliminating the ambiguity caused by circuit mixing.
Solution Approach 2:
Each protection device independently monitors the quality and status of its own local current transformer circuits while obtaining remote measurements through communication channels. This local quality monitoring enables reliable differentiation between primary faults (affecting the protected object) and secondary faults (affecting local measurement circuits).
3Reliability
If circuit breaker tripping is activated upon fault detection, then protection isolation is achieved, but unnecessary tripping may occur due to undetected secondary faults in current transformer circuits
Solution Approach 1:
The system performs preliminary comparison of measured values from both ends before activating circuit breaker tripping. By independently verifying that fault indicators appear at both ends (indicating a primary fault) rather than at only one end (indicating a secondary local fault), the system prevents unnecessary tripping while maintaining effective isolation for genuine primary faults.
Solution Approach 2:
Each protection device receives feedback from the other end through communication channels, allowing verification of whether fault indicators are consistent across both ends. This feedback mechanism ensures that tripping commands are issued only when primary faults are confirmed, preventing unnecessary disconnections caused by undetected secondary faults.
Data Source
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AI summary
The invention relates to a differential protection method in a power network for determining type of fault occurring within the power network. The power network comprises a protected object having two or more ends, and a current differential protection device (12, 14) and a current transformer (11, 13) are arranged at each end (A, B). The method comprises the steps: obtaining, at a first end of the protected object, measured values from a second end of the protected object; comparing, at the first end, changes in measured values taken at the first end with changes in the measured values obtained from the second end; and determining, upon the step of comparing changes in measured values showing differing results, type of fault occurring within the power network.