Transformer Differential Protection Using Zero-Sequence Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Differential protection methods for multi-phase transformers face challenges in reliably distinguishing between external and internal faults, particularly due to zero-current correction issues during high-current loads and converter saturation, leading to false tripping.
Innovation Solution
Incorporating the zero-sequence system current into the calculation of stabilization values by determining the maximum value from measured current values and zero-sequence currents flowing through the transformer, which helps in forming sufficient restraint values during faults, thereby reducing the risk of false tripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If zero-current correction is performed during high-current loads, then measurement accuracy is improved, but false tripping occurs due to converter saturation
Solution Approach 1:
The patent applies preliminary action by performing saturation detection before final fault determination. The system detects converter saturation in advance by monitoring the relationship between primary and secondary currents, and adjusts the protection logic accordingly to prevent false tripping while maintaining measurement accuracy during high-current loads
Solution Approach 2:
The patent implements dynamics by making the tripping threshold adaptive rather than fixed. The system dynamically adjusts the differential current threshold based on the stabilization value and detected saturation conditions, allowing the protection scheme to adapt its sensitivity according to the actual operating state and prevent false tripping during high-current scenarios
2Measurement precision
If differential protection sensitivity is increased to detect internal faults, then fault detection capability is improved, but false tripping increases during external faults
Solution Approach 1:
The patent uses dynamics by implementing an adaptive tripping threshold that changes based on operating conditions. The threshold is calculated as a function of the stabilization value and is adjusted according to detected saturation levels, enabling the system to maintain high sensitivity for internal faults while automatically reducing sensitivity during external faults to prevent false tripping
Solution Approach 2:
The patent applies feedback by continuously monitoring the relationship between primary and secondary currents and using this information to adjust the protection logic. The system feeds back saturation detection results to modify the tripping decision, creating a closed-loop control that prevents false tripping while maintaining fault detection capability
3Device complexity
If stabilization values are calculated without considering zero-sequence current, then calculation simplicity is maintained, but restraint values are insufficient during high-current faults
Solution Approach 1:
The patent applies merging by combining the zero-sequence current component with the phase current measurements in the stabilization value calculation. This integration ensures that the stabilization value reflects the total current magnitude including zero-sequence components, providing sufficient restraint during high-current faults while maintaining a unified and relatively simple calculation framework
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention relates to a differential protection method for generating an error signal, in which current measured values are respectively measured at at least two different measuring points (M1, M2) of a multiphase transformer (10) for each phase (A, B, C), the current measured values for each phase (A, B, C) are used to form differential current values and stabilization values, and the error signal is generated if it is determined during a trigger range test that a measured value pair of at least one of the phases (A, B, C), which is formed using one of the differential current values and the associated stabilization value in each case, is in a predefined trigger range (23). In order to be able to selectively and reliably distinguish an external error from an internal error, if the transformer (10) has an earthed neutral point (14), it is proposed that a zero phase-sequence system current flowing through the neutral point (14) is used to form the stabilization values. The invention also relates to a corresponding differential protection device (11) for performing such a differential protection method.