Instrument Transformer Burden Testing with MOSFET Switching
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Solution Overview
Problem
Current burden testing methods for instrument transformers face inaccuracies due to varying primary currents, internal heating, and transformer magnetization, which can lead to flux offset and reduced measurement accuracy, and require lengthy test cycles and heavy, unwieldy resistors with limited lifespan.
Innovation Solution
The method involves using high-speed MOSFET switches controlled by a microprocessor and DSP to synchronize burden insertion and removal with zero crossings of the signal, allowing for single-cycle measurements and flexible burden configurations, reducing test time and heat dissipation, and using a composite burden resistor array mounted on a heat sink for efficient heat management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional burden testing methods are used with heavy resistors and lengthy test cycles, then measurement accuracy is maintained, but test time increases and equipment lifespan decreases
Solution Approach 1:
The patent replaces traditional mechanical relay-based burden switching with solid-state MOSFET switches. This substitution enables precise control of burden insertion and removal timing, allowing single-cycle measurements while eliminating the mechanical wear and lengthy operation times associated with traditional relays. The solid-state switches provide rapid, accurate switching that maintains measurement precision without requiring lengthy test cycles.
Solution Approach 2:
The patent implements periodic action by synchronizing burden insertion and removal with the zero-crossing points of the AC waveform. This timing strategy allows the burden to be applied only during the necessary measurement window (single cycle), minimizing heat dissipation and test time while maintaining accurate measurements. The periodic synchronization ensures that measurements are taken at optimal points in the waveform cycle.
2Reliability
If traditional burden resistors are used, then testing can be performed, but heat dissipation increases and equipment lifespan decreases
Solution Approach 1:
The patent replaces traditional high-power burden resistors with a composite burden resistor array configured in series and parallel combinations. This array, controlled by solid-state MOSFET switches, achieves the same burden effect with significantly reduced power dissipation. The solid-state switching eliminates the need for continuously dissipating heat through large resistors, thereby extending equipment lifespan and reducing energy loss.
Solution Approach 2:
The patent segments the burden resistance into multiple smaller resistors arranged in series and parallel configurations. This segmentation allows precise control of the total burden value and enables the system to achieve the required measurement effect with lower individual resistor power ratings. The segmented approach reduces overall heat dissipation compared to using a single large burden resistor.
3Productivity
If burden testing is performed during operation, then continuous monitoring is enabled, but flux offset and measurement inaccuracies occur
Solution Approach 1:
The patent applies preliminary action by inserting the burden exactly at the zero-crossing point before the measurement cycle begins, and removing it immediately after the single measurement cycle completes. This timing ensures that the transformer core is not subjected to prolonged magnetization that would cause flux offset, while still enabling continuous monitoring capability. The preliminary and precise timing of burden application prevents measurement inaccuracies.
Solution Approach 2:
The patent implements skipping by completing the entire measurement process within a single AC cycle, rushing through the measurement before flux offset can develop. This single-cycle approach allows continuous monitoring while preventing the transformer magnetization and flux offset that would otherwise cause measurement inaccuracies during longer test durations.
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
This approach minimizes inaccuracies by reducing test time, heat dissipation, and the need for costly relays, while ensuring accurate measurements and extending the lifespan of burden resistors, and effectively demagnetizes the transformer core, resulting in a more efficient and safer testing process.
Implementation Method 1
switching the solid state switch to place the test load in circuit with the transformer
Implementation Method 2
composite burden resistor array mounted on a heat sink for efficient heat management
Implementation Method 3
high-speed MOSFET switches controlled by a microprocessor and DSP to synchronize burden insertion and removal with zero crossings of the signal
Data Source
Figure 1
Figure 2
Figure 3a
AI summary
A method and apparatus for testing a transformer. A controller generates a switching signal and supplies the switching signal to a solid state switch in circuit with a test load of known magnitude, switching the solid state switch to place the test load in circuit with the transformer. A signal through or across the transformer is then measured. Methods and apparatus for testing a transformer comprise the controller and solid state switch placing a series of test loads of different known magnitudes in circuit with the transformer from the lowest magnitude to the highest, from the highest to the lowest, or both. Additionally, a test load array comprises a plurality of power resistors, a heat sink for accommodating the plurality of power resistors, and a material providing electrical insulation of the power resistors from the heat sink and thermal conductivity between the power resistors and the heat sink.