Current Transformer Excitation Testing via DC Voltage
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Solution Overview
Problem
Conventional methods for testing the excitation characteristic of current transformers, such as the power-frequency method, require high voltages, limiting their application scope and posing safety risks, especially for class-P and class-TP protective CTs used in extra-high and ultra-high voltage systems.
Innovation Solution
A method and apparatus that apply alternately positive and negative DC voltages across the secondary winding of current transformers to acquire a secondary current, constructing a mathematical model relating the magnetic flux and rms equivalent voltage, and generating an excitation characteristic curve, allowing for lower voltage testing and increased accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If power-frequency voltage is applied across the secondary winding to test excitation characteristic, then the excitation characteristic can be measured, but high voltage (2kV or higher, even up to over 20kV) is required which poses safety risks and limits application scope
Solution Approach 1:
The patent changes the voltage type parameter from power-frequency AC voltage to DC voltage for testing. By applying DC voltage to the secondary winding and measuring the resulting current, the excitation characteristic can be obtained without requiring high voltage. The DC voltage method transforms the testing approach while maintaining measurement accuracy, thereby eliminating the safety risks associated with high voltage power-frequency testing.
2Measurement precision
If power-frequency voltage is applied across the secondary winding to test excitation characteristic, then the excitation characteristic can be measured, but large device capacity is required which increases complexity and cost
Solution Approach 1:
The patent changes the voltage type parameter from power-frequency AC voltage to DC voltage for testing. By applying DC voltage to the secondary winding and measuring the resulting current, the excitation characteristic can be obtained without requiring high voltage. The DC voltage method transforms the testing approach while maintaining measurement accuracy, thereby eliminating the safety risks associated with high voltage power-frequency testing.
3Measurement precision
If power-frequency voltage is applied across the secondary winding to test excitation characteristic, then the excitation characteristic can be measured, but the application scope is limited to CTs with lower knee-point voltage
Solution Approach 1:
The patent changes the voltage type parameter from power-frequency AC voltage to DC voltage for testing. By applying DC voltage to the secondary winding and measuring the resulting current, the excitation characteristic can be obtained without requiring high voltage. The DC voltage method transforms the testing approach while maintaining measurement accuracy, thereby eliminating the safety risks associated with high voltage power-frequency testing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the testing of current transformers with knee-point voltages up to tens of kV using relatively low voltage and power, enhancing safety and applicability while providing accurate excitation characteristic curves.
Implementation Method 1
A CT transforms a higher primary current to a lower secondary current (or current in the secondary loop) with a certain ratio through core coupling based on the principle of electromagnetic induction
Implementation Method 2
In order to transfer energy between the first and second windings, the CT has to first establish magnetic field
Data Source
AI summary
This disclosure relates to the field of current transformers, for testing the excitation characteristic of a current transformer is disclosed. The method comprise applying alternately positive and negative DC voltages across terminals of secondary winding of a CT to be tested and acquiring a secondary current; constructing a mathematical model of the relationship between the secondary current and a root mean square (rms) equivalent voltage at rated frequency of the CT from the relationship between a magnetic flux of a secondary winding iron-core of the CT and the rms equivalent voltage; and generating an excitation characteristic curve according to the mathematical model. The method and apparatus of the embodiments may test CTs requiring lower testing voltage as well as CTs with knee-point up to tens of kV by supplying a relatively low voltage and power, which makes the embodiments widely applicable.