Digital Protective Relay DC Component Disturbance Detection
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Solution Overview
Problem
Conventional self-power relays experience delays and malfunctions due to initial sample values including electrical disturbances from DC components, restricting instantaneous relay operations and affecting initial relay performance.
Innovation Solution
A method for detecting electrical disturbances by a DC component using adjacent sample values, allowing for instantaneous relay operations by comparing differences between sample values and setting reference values based on sampling cycles and breaking currents, thereby preventing malfunctions and improving stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional self-power relay performs DFT on a minimum 1/2 cycle sample value to remove DC component effects, then the relay operation reliability is improved by removing electrical disturbances, but the relay operation time is increased causing a delay of about one cycle and restricting instantaneous relay operation
Solution Approach 1:
The patent applies preliminary action by detecting electrical disturbances using only two adjacent sample values before performing DFT transformation. The disturbance detection unit compares the difference between adjacent sample values with a predetermined threshold to identify disturbances in advance, allowing the relay to skip unnecessary DFT calculations and achieve instantaneous operation while maintaining reliability through selective disturbance rejection
Solution Approach 2:
The patent uses partial action by performing DFT transformation on only two sample values instead of the conventional minimum 1/2 cycle samples. This partial sampling approach is sufficient for disturbance detection and DC component removal, significantly reducing the transformation time while maintaining the reliability needed for accurate relay operation decisions
2Speed
If the conventional self-power relay uses initial sample values for relay operation, then the relay operation speed is improved, but malfunction may occur due to DC component interference in the initial samples
Solution Approach 1:
The patent extracts and removes the harmful DC component from the initial sample values before relay operation. The disturbance detection unit identifies DC components by comparing adjacent sample values, and the DFT transformation on these two values removes the DC effect, leaving only the useful AC component information for reliable and fast relay operation
Solution Approach 2:
The patent introduces an intermediate disturbance detection and removal process between sample acquisition and relay operation. By using two sample values as an intermediary step to detect and remove DC components, the system enables both fast operation (using initial samples) and reliable operation (free from DC interference)
Data Source
AI summary
The present disclosure relates a method of detecting an electrical disturbance by a DC component in a digital protective relay, which includes acquiring a sample value by sampling an input signal at a regular cycle, detecting the electrical disturbance based on a difference between a sampled first sample value and a second sample value after the first sample value, and when the electrical disturbance is detected, detecting the DC component based on a difference between the second sample value and a third sample value after the second sample value and a difference between the third sample value and a fourth sample value after the third sample value.