Current Transformer Control Circuit for DC Measurement Accuracy
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Solution Overview
Problem
Existing current transformers face inaccuracies in measuring alternating-current (a-c) and direct-current (d-c) currents, especially when d-c currents are present, due to core magnetization and saturation issues, leading to fluctuations in magnetic flux and errors in current measurement.
Innovation Solution
The use of a common electronic control circuit to provide magnetic control for multiple current transformers, employing voltage pulses or continuously adjustable voltages to manage the magnetization of the magnetic core, ensuring accurate measurement of a-c and d-c currents by demagnetizing the core and minimizing flux variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common electronic control circuit is used to provide magnetic control for multiple current transformers, then device complexity is reduced and cost is lowered, but measurement precision may be compromised due to shared control resources
Solution Approach 1:
The patent combines multiple current transformer control functions into a single electronic control circuit that can sequentially control multiple current transformers. This merging approach reduces device complexity and cost while maintaining measurement precision through time-division multiplexing, where each current transformer is measured in sequence during different time intervals.
Solution Approach 2:
The electronic control circuit is designed with universal functionality to control multiple different types of current transformers (measuring different currents such as Ia, Ib, Ic) through the same control mechanisms. This multi-functionality allows a single circuit to perform what would traditionally require multiple dedicated circuits, reducing complexity while maintaining accuracy for each measurement.
2Measurement precision
If voltage pulses are used to demagnetize the magnetic core, then measurement accuracy for d-c currents is improved, but the complexity of the control circuit increases
Solution Approach 1:
The patent employs periodic voltage pulses applied to the magnetic core at specific intervals to demagnetize it and prevent saturation. This periodic action occurs during designated time intervals between current measurements, allowing the core to be reset without interfering with the measurement process. The demagnetizing pulses are applied in a rhythmic, periodic manner that coordinates with the measurement sequence.
Solution Approach 2:
The magnetic core is demagnetized using voltage pulses before actual current measurements are taken. This preliminary action ensures the core starts each measurement cycle in a demagnetized state, preventing accumulation of magnetic flux that would cause measurement errors. The demagnetizing process is completed in advance of each measurement sequence.
3Device complexity
If multiple current transformers are controlled sequentially by a common circuit, then cost is reduced, but measurement speed decreases compared to parallel control
Solution Approach 1:
Multiple current transformers are controlled in sequential periodic intervals rather than simultaneously. Each current transformer is activated for measurement during its designated time slot, with the common control circuit switching between them in a periodic sequence. This time-division approach reduces the number of control circuits needed while maintaining acceptable measurement throughput for power monitoring applications.
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 enhances the accuracy of current measurement by reducing errors associated with core magnetization and saturation, allowing for precise measurement of a-c and d-c currents, including those with d-c components, at a lower cost compared to competing technologies.
Implementation Method 1
The varying voltage controls the voltage induced in the winding in such a way that the integral over time of the induced voltage correlates to desired changes of the induction of the magnetic body
Implementation Method 2
Existing current transformers face inaccuracies in measuring alternating-current (a-c) and direct-current (d-c) currents, especially when d-c currents are present, due to core magnetization and saturation issues
Data Source
AI summary
Apparatus for measuring multiple primary electric currents in a non-contact manner by utilizing multiple current transformers. Each current transformer is coupled with one of the primary electric currents. Each current transformer comprises a magnetic core and a secondary winding. The apparatus comprises: A current-sensing means for sensing current transformer secondary currents and for producing an information signal; a voltage control and selection circuit for periodically connecting each current transformer secondary winding to the current-sensing means and for periodically controlling the voltage across each secondary winding; a power supply circuit for providing operating power to the voltage control and selection circuit; and a control circuit for receiving and processing the information signal and for controlling the voltage control and selection circuit. The control circuit and the voltage control and selection circuit function to select and control the multiple current transformers for periodic measurement of the multiple primary electric currents.