Transformer Voltage Estimation via Sequence Components
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Solution Overview
Problem
Measuring voltages at the high voltage side of a transformer is complex and costly, especially when connected to medium-voltage grids, and existing methods for fault detection based on low voltage side measurements are inadequate for accurately determining faults at the high voltage side, particularly for transformers without a neutral line.
Innovation Solution
A method that measures delta and string voltages, along with phase angles at the low voltage side, transforms these into positive, negative, and zero-sequence voltages and angles, and estimates the corresponding parameters at the high voltage side, allowing for qualitative and quantitative fault detection without direct measurement at the high voltage side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltages are measured directly at the high voltage side of the transformer, then measurement accuracy and reliability are improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent uses the transformer itself as an intermediary to transfer voltage information from the high voltage side to the low voltage side. By measuring voltages at the low voltage side and using the known transformer ratio, the system indirectly obtains high voltage side voltage information without direct measurement, thus avoiding the complexity of high voltage measurement equipment.
Solution Approach 2:
The patent creates a scaled-down copy of the high voltage side voltage conditions by measuring corresponding voltages at the low voltage side. The measurement system effectively works with a copy of the voltage information that has been transformed to a safer, more manageable voltage level while preserving the essential fault detection capabilities.
2Device complexity
If voltage measurements are performed at the low voltage side of the transformer, then device complexity is reduced, but measurement precision and fault detection accuracy deteriorate for certain transformer types
Solution Approach 1:
The patent changes the parameters being measured from simple voltage magnitudes to a comprehensive set including voltage magnitudes, phase angles, and sequence components (positive, negative, and zero sequence). By transforming and analyzing these multiple parameters in combination, the system overcomes the limitations of simple voltage measurement and achieves accurate fault detection even without direct high voltage side measurement.
Solution Approach 2:
The patent measures more parameters than traditionally required (including both magnitude and phase angle, and decomposing into sequence components), which provides redundant information that compensates for the indirect measurement approach. This excessive measurement of parameters ensures that sufficient information is available to accurately detect faults despite the transformation process.
3Loss of information
If zero-sequence voltage information is not transmitted through the transformer, then information loss occurs, but measurement safety and simplicity are improved
Solution Approach 1:
The patent performs preliminary decomposition of the voltage signals into sequence components at the low voltage side before transformation. By calculating the zero-sequence component from the available low voltage side measurements and using the transformer's known characteristics, the system prepares the necessary information in advance to compensate for what would otherwise be lost during transformation.
Solution Approach 2:
The patent uses feedback from the measured low voltage side parameters to continuously update and refine the estimation of high voltage side conditions. By comparing expected transformer behavior with actual measurements and adjusting the analysis accordingly, the system compensates for information loss and maintains accurate fault detection capability.
Data Source
AI summary
The disclosure relates to a method and related device for approximately determining voltages at a high-voltage side of a transformer on the basis of measured voltages at a low-voltage side of the transformer. The method includes measuring delta voltages and phase voltages and phase angles at the low-voltage side of the transformer, transforming the phase voltages and phase angles into positive and negative phase sequence system voltages and phase angles of the positive and negative phase sequence systems, respectively, at the low-voltage side, determining positive and negative phase sequence system voltages and phase angles of the positive and negative phase sequence systems, respectively, at the high-voltage side from the positive and negative phase sequence system voltages and phase angles of the positive and negative phase sequence systems, respectively, at the low-voltage side, determining estimated values of a zero phase sequence system voltage and of a phase angle of a zero phase sequence system at the high-voltage side from the measured delta voltages and phase voltages and phase angles at the low-voltage side, and transforming the positive, negative and zero phase sequence system voltages and the phase angles into phase voltages and/or delta voltages at the high-voltage side of the transformer.