Non-Contact Cable Voltage Measurement Using Injection Current
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Solution Overview
Problem
Existing non-contact voltage measurement methods, such as those described in PTL 1, suffer from inaccuracies due to variations in insulator capacitance caused by factors like temperature and humidity, leading to potential electric shocks, short circuits, and loss of measurement data when measuring live wire sections in switchboards.
Innovation Solution
A measurement apparatus and method that injects an injection current with a second frequency into a core wire through an insulator, acquires a composite current composed of the injection and leakage currents, calculates active and reactive powers, and determines the voltage based on these powers and frequencies, allowing accurate measurement from the cable sheath without direct contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a clip is connected to a live wire section to measure voltage, then measurement can be performed, but there is a risk of electric shock to the operator and short circuit
Solution Approach 1:
The patent introduces a magnetic core as an intermediary element that couples with the live wire section through magnetic flux. The measurement clip attaches to this magnetic core rather than directly to the live wire, allowing voltage measurement through electromagnetic induction while maintaining electrical isolation. This mediator approach enables measurement capability while eliminating direct electrical contact and associated safety risks.
2Object-affected harmful factors
If measurement is performed through an insulator in contact with the core wire, then safety risks are reduced, but measurement precision may be affected by coupling capacitance variations
Solution Approach 1:
The patent replaces the direct electrical contact measurement system with an electromagnetic field-based measurement system. Instead of measuring voltage through electrical contact with the insulator, the system uses a magnetic core that generates magnetic flux proportional to the wire current, which is then converted to a measurable signal. This substitution of measurement mechanism eliminates the coupling capacitance issue while maintaining safety.
3Object-affected harmful factors
If a magnetic core is used for non-contact measurement, then safety is improved, but device complexity increases due to additional components
Solution Approach 1:
The magnetic core serves multiple functions simultaneously: it acts as a magnetic coupling element for voltage measurement, provides mechanical support for the measurement clip, and creates the necessary magnetic flux path for electromagnetic induction. By making the magnetic core multi-functional, the patent reduces the need for additional separate components, thereby limiting the increase in device complexity while maintaining safety improvements.
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 precise measurement of voltage and phase of leakage current with reduced environmental influences, minimizing risks of electric shock and short circuits, and ensuring accurate data acquisition from live wire sections.
Implementation Method 1
a measurement apparatus that measures voltage applied to a core wire by measuring magnetic flux
Data Source
AI summary
A measurement apparatus includes a controller configured to inject an injection current with a second frequency through an insulator into the core wire, to which the voltage to be measured, with a first frequency, is applied, acquire a composite current in which the injection current and a leakage current of the voltage to be measured having leaked out of the core wire through the insulator are superimposed in a circuit unit, calculate, by analyzing the composite current, measured active and reactive powers equivalent to active and reactive powers based on a contribution of the voltage to be measured, calculate the voltage to be measured, based on the measured active and reactive powers, the first and second frequencies, a voltage of the injection current, and a current effective value of the leakage current, and output the calculated voltage to be measured.