Contactless AC Power Measurement via Capacitive and Inductive Coupling
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Solution Overview
Problem
Existing AC power measurement methods require direct contact with conductor wires, posing safety risks and making it difficult to accurately measure active power without turning off the power supply, and suffer from phase errors due to differences in electrostatic capacitance between voltage sensors and cables.
Innovation Solution
A contactless AC power measuring apparatus using electrostatic capacitance coupling for voltage detection and electromagnetic induction coupling for current detection, with a processing unit normalizing voltage waveforms to account for grounding types, allowing for accurate line-to-line voltage computation and power measurement without physical contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct contact measurement is used to obtain accurate voltage and current waveforms, then measurement precision is improved, but safety risks increase and power supply must be turned OFF
Solution Approach 1:
The patent introduces an insulating rod as an intermediary medium between the voltage sensor and the conductor wire. The voltage sensor is mounted on the insulating rod which is then brought near the conductor wire for measurement. This intermediary allows the sensor to detect voltage waveforms accurately through capacitive coupling without direct electrical contact, eliminating safety risks while maintaining measurement precision.
Solution Approach 2:
The patent replaces direct mechanical/electrical contact measurement with non-contact capacitive coupling for voltage measurement and electromagnetic induction for current measurement. By using the insulating rod to position the sensor near the conductor and utilizing field-based detection methods, the system eliminates the need for direct electrical contact while maintaining accurate waveform detection.
2Reliability
If contactless measurement by electrostatic capacitance coupling is used for voltage detection, then safety is improved and power supply remains ON, but phase errors occur due to differences in electrostatic capacitance
Solution Approach 1:
The patent applies parameter change by introducing a correction coefficient that compensates for phase errors caused by varying electrostatic capacitance. The processing unit calculates this correction coefficient based on the relationship between the insulating rod's position and the conductor wire, then applies it to correct the detected voltage waveform phase, thereby maintaining measurement precision while preserving the safety advantages of contactless measurement.
3Ease of operation
If voltage sensors are placed at different distances from conductor wires, then ease of operation is improved, but measurement precision deteriorates due to inconsistent electrostatic capacitance
Solution Approach 1:
The patent implements feedback by having the processing unit detect the position of the insulating rod relative to the conductor wire and calculate a correction coefficient based on this position information. This correction coefficient is then applied to compensate for the effects of varying electrostatic capacitance, allowing the system to maintain high measurement precision even when the sensor is positioned at different distances for ease of operation.
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 safe, accurate, and non-contact measurement of AC power by eliminating phase errors and inconsistencies in voltage waveforms, ensuring precise computation of active power without disrupting the power supply.
Implementation Method 1
a voltage detecting unit configured to detect voltage waveforms of each of phases of a set of three insulated cables for supplying a three-phase A.C. power to a load, by performing a contactless measurement by electrostatic capacitance coupling
Implementation Method 2
a current detecting unit configured to detect current waveforms of the set of three insulated cables, by performing a contactless measurement by electromagnetic induction coupling
Data Source
AI summary
An A.C. power measuring apparatus includes a voltage detecting unit that detects voltage waveforms of each of phases of a set of insulated cables for supplying a three-phase A.C. power to a load, by performing a contactless measurement by electrostatic capacitance coupling, and a current detecting unit that detects current waveforms of the set of insulated tables, by performing a contactless measurement by electromagnetic induction coupling. The apparatus further includes a processing unit that computes a power to be supplied to the load, based on line-to-line voltage waveforms, the current waveforms, and prescribed voltage values, by normalizing the voltage waveforms of each of the phases so that as amplitude ratio of the voltage waveforms becomes in accordance with a grounding type of the three-phase A.C. power, and obtaining the line-to-line voltages of the set of three insulated cables based on the normalized voltage waveforms of each of the phases.