Converter Transformer Inter-Turn Protection Under Harmonic Blocking
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Solution Overview
Problem
Existing protection methods for converter transformers fail to quickly identify and isolate inter-turn short-circuit faults due to the difficulty in distinguishing transient short-circuit currents from magnetizing inrush currents, especially in high-voltage systems, leading to rapid fault development and potential device damage.
Innovation Solution
An inter-turn protection method and system that calculates three-phase differential currents, fundamental and second harmonic effective values, and positive/negative sequence component sums of differential current variations, using preset criteria to determine inter-turn protection actions based on these calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential protection with second harmonic blocking function is used, then magnetizing inrush current malfunctioning is prevented, but inter-turn fault detection speed is reduced due to long blocking time
Solution Approach 1:
The patent segments the protection logic into two independent parts: the existing differential protection with second harmonic blocking, and the new inter-turn protection based on zero-sequence current. This segmentation allows both protection functions to operate simultaneously without interfering with each other, thus maintaining reliability while improving detection speed for inter-turn faults.
Solution Approach 2:
The patent introduces zero-sequence current as an intermediary parameter to detect inter-turn faults. By using the zero-sequence component of the differential current, the system can identify inter-turn faults without being affected by the second harmonic blocking mechanism, thus bypassing the speed limitation while maintaining reliability.
2Reliability
If second harmonic blocking is applied to prevent inrush current false trips, then protection reliability is improved, but fault isolation time is extended
Solution Approach 1:
The patent performs preliminary detection of inter-turn faults using zero-sequence current analysis before the second harmonic blocking expires. By continuously monitoring the zero-sequence component, the system can identify faults in advance and prepare for rapid isolation, thus reducing the overall fault isolation time while maintaining protection reliability.
Solution Approach 2:
The patent implements a feedback mechanism where the inter-turn protection continuously monitors zero-sequence current and provides real-time fault detection. This feedback allows the system to quickly respond to developing faults without waiting for the second harmonic blocking to expire, thereby reducing fault isolation time while maintaining reliability through the robust differential protection framework.
3Adaptability or versatility
If conventional differential protection is used, then general internal faults are detected, but rapid developing inter-turn faults cannot be quickly identified due to harmonic blocking
Solution Approach 1:
The patent adds another dimension to the protection by introducing zero-sequence current analysis as a separate detection channel. This dimensional addition allows the system to detect rapid inter-turn faults through a different parameter space that is not affected by second harmonic blocking, thereby improving measurement precision for this specific fault type while maintaining versatility for general internal fault detection.
Solution Approach 2:
The patent changes the detection parameter from conventional differential current (affected by harmonics) to zero-sequence current (less affected by harmonics). This parameter change enables more precise detection of rapid inter-turn faults by using a parameter that maintains its effectiveness even when second harmonic blocking is active, thus improving measurement precision without sacrificing adaptability.
Data Source
AI summary
The present application provides an inter-turn protection method and system for a converter transformer. In the method and system, three-phase currents before and after initiating inter-turn protection are collected at a valve side and at a grid side of a converter transformer, and a three-phase differential current, a three-phase differential current variation, and a fundamental phasor of the sum of positive and negative sequences of the three-phase differential current variation of the converter transformer are calculated according to the three-phase current; then, criterion results for a differential protection criterion, a second harmonic blocking criterion, a waveform identification open criterion, and a sequence differential current open criterion are determined according to the calculated parameter values; and last, whether inter-turn protection actuates is determined according to the criterion results. When a developmental inter-turn short circuit fault occurs in a converter transformer and differential protection can not rapidly identify and remove the fault due to the time for second harmonic blocking being relatively long, the present method and system quickly perform inter-turn protection action output, and protection sensitivity and action speed during an inter-turn fault are greatly improved.