Self-Shielded Di/Dt Transformer for Metering
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Solution Overview
Problem
Existing current sensors in electricity meters, such as current transformers (CTs), are prone to saturation and errors, especially in DC magnetic fields or half-wave rectified loads, requiring additional costly circuitry to compensate, and are complex and expensive to manufacture due to the need for precise winding configurations.
Innovation Solution
A current sensor arrangement featuring a non-magnetic core with bifilar windings and an integrating amplifier circuit, along with a DC stabilization circuit, which includes resistive paths to generate a phase shift and stabilize DC signals, reducing errors and production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional current transformers are used for current measurement, then the measurement can be obtained, but the sensor is prone to saturation and distortion errors especially in DC magnetic fields or half wave rectified loads
Solution Approach 1:
The patent changes the fundamental operating parameters of the current sensor by using an integrating amplifier circuit that measures the area under the current waveform rather than the instantaneous current. This integration approach transforms the measurement parameter from amplitude to accumulated value, making the system immune to DC offsets and half-wave rectification effects that cause saturation in traditional CTs.
Solution Approach 2:
The patent replaces the traditional electromagnetic induction mechanism of current transformers with an electronic integration-based measurement system. Instead of relying on magnetic coupling and transformer ratios, the invention uses an integrating amplifier with feedback winding to electronically compute the current measurement, eliminating magnetic saturation issues inherent in electromagnetic systems.
2Measurement precision
If additional circuitry is added to compensate for CT errors, then measurement accuracy under various circumstances improves, but production cost increases
Solution Approach 1:
The patent implements a self-compensating measurement system where the integrating amplifier automatically corrects for DC offsets and half-wave rectification errors through its inherent integration function. The feedback winding and integrator circuitry naturally eliminate measurement errors without requiring additional compensation circuitry or complex calibration systems, thereby reducing production costs while maintaining high accuracy.
3Measurement precision
If precise winding configurations are required in CTs to avoid errors, then measurement accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces the mechanically complex precise winding requirements of traditional CTs with an electronic integration system. The feedback winding in the integrating amplifier requires less precise turns ratios because the integration process inherently compensates for winding imperfections. This substitution of electromagnetic induction with electronic integration dramatically reduces manufacturing complexity while maintaining or improving accuracy.
4Adaptability or versatility
If traditional CT designs are used, then current measurement is achieved, but the sensor distorts and causes error in DC magnetic fields or half wave rectified loads
Solution Approach 1:
The patent fundamentally changes the measurement parameter from instantaneous current amplitude to integrated area under the waveform. This parameter transformation enables the system to accurately measure current in DC magnetic fields and half-wave rectified loads conditions where traditional CTs fail, as the integration process naturally handles non-sinusoidal and DC-containing waveforms without distortion.
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
The solution provides high accuracy over a larger dynamic range, immunity to AC and DC fields, and reduced component count, achieving accuracy better than 0.05% with lower costs and simpler manufacturing, while maintaining immunity to external influences and aging-related fluctuations.
Implementation Method 1
The first winding is configured to generate a magnetic field around the core in response to current flowing through the first winding
Implementation Method 2
The second winding is configured to generate a voltage in response to a magnetic field generated by the first winding
Data Source
AI summary
A sensor includes a core, first and second windings, an integrating amplifier circuit and a DC stabilization circuit. The first and second windings are wrapped around the core. The integrating amplifier circuit has a first input coupled to receive a sensed current from the first winding, and an output operably coupled to provide a current the second winding. The integrating amplifier circuit is configured to generate a phase shift from an input current received at the first input and the current provided to the second winding. The DC stabilization circuit includes a first resistive path coupled between the output of the integrating amplifier circuit and the first input of the integrating amplifier circuit, and a second resistive path coupled between the first winding and the first input of the integrating amplifier circuit.