Inductor-Based Current Measurement in Electric Meters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for measuring current in electric meters, such as resistive shunts, face challenges like temperature-induced resistance changes, increased cost, and high power dissipation, especially in high-power meters, making them complex and costly.
Innovation Solution
A system using an inductor positioned in series with the current flowing through bus bars, where a voltage detector monitors the voltage across the inductor, and a control unit calculates the current based on the sensed voltage, with a calibration process determining the inductance and series resistance values for accurate current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistive shunt is used to measure current, then current measurement is achieved, but the shunt heats up and resistance changes with temperature requiring temperature compensation
Solution Approach 1:
The patent replaces the resistive shunt (electrical measurement system) with a magnetic field-based sensing system using a Rogowski coil or current transformer. This substitution eliminates the need for direct electrical contact and temperature-compensated resistance measurements, as the magnetic field sensing is inherently temperature-stable.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary between the current being measured and the measurement system. Instead of directly measuring voltage across a resistive shunt, the system measures the magnetic field generated by the current, which then gets converted to a measurable signal. This intermediary approach avoids the temperature-dependent resistance issue.
2Measurement precision
If a resistive shunt is used in high power electric meters of 100 amps or more, then current measurement is achieved, but too much power is dissipated
Solution Approach 1:
The patent replaces the resistive shunt with a magnetic field-based sensing system that has negligible power consumption. The Rogowski coil or current transformer senses the magnetic field generated by the load current without drawing significant power, unlike the resistive shunt which dissipates I²R losses that become substantial at 100 amps or more.
Solution Approach 2:
The patent extracts the measurement function from the current path itself. Instead of forcing current through a resistive element to create a measurable voltage drop, the system extracts information about the current by sensing the magnetic field it generates, allowing the current to flow through its normal low-resistance path without power dissipation.
3Measurement precision
If a Rogowski coil or current transformer is used to measure current, then current measurement is achieved, but additional cost is added to the meter
Solution Approach 1:
The patent extracts only the essential measurement function from complex commercial Rogowski coils or current transformers. By using simplified magnetic sensing elements and integrating the measurement function into the meter's existing circuitry, the system achieves current measurement capability at a lower cost than purchasing complete commercial sensors.
Solution Approach 2:
The patent merges the current sensing function with the meter's existing measurement and processing circuitry. Instead of using a standalone commercial Rogowski coil or current transformer that comes with its own signal conditioning and processing, the system integrates the magnetic sensing element directly into the meter's circuit board, sharing resources and reducing overall cost.
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 provides accurate current measurement without the need for temperature compensation and reduces costs by eliminating the need for expensive components, while maintaining precision across varying power levels.
Implementation Method 1
The current flowing through the bus bars passes through the inductor and generates a voltage across the inductor
Data Source
AI summary
A method and system for measuring the current flowing through an electric meter. The electric meter includes a reactive sensor positioned in series with a bus bar contained in the meter. The reactive sensor includes an inductor and the voltage across the inductance is measured. A control unit contained in the electric meter calculates the current based on the detected voltage and the value of the inductor. The value of the inductor is determined by passing a reference current through the inductor at a known frequency, such as 50 Hz or 60 Hz, and the voltage drop across the inductor is measured. Once the value of the inductor is determined, the value is stored in the control unit.