Insulation Deterioration Diagnosis Using Preliminary Core Magnetization
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Solution Overview
Problem
Existing insulation deterioration diagnostic apparatuses for inverter-driven load devices struggle to precisely measure minute leakage currents across a wide range of frequencies due to limitations in zero-phase current transformers, such as frequency-dependent magnetic characteristics and sensitivity issues, which hinder early detection and continuous operation diagnostics.
Innovation Solution
The proposed solution involves an insulation deterioration diagnostic apparatus with a zero-phase current transformer having an annular magnetic core, a magnetizing coil, and a detecting coil, along with a magnetization control circuit that supplies alternating current at a frequency twice that of the drive frequency to magnetize the core, and a frequency extracting circuit to correct for frequency-dependent sensitivity, allowing for precise measurement of leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a zero-phase current transformer is used to detect leakage current, then the measurement can be performed continuously without stopping power supply, but the measurement precision deteriorates at low drive voltage frequencies due to frequency-dependent magnetic characteristics
Solution Approach 1:
The magnetic core is preliminarily magnetized by applying a magnetizing current before leakage current detection. This preliminary magnetization ensures that the magnetic core operates in a stable region with consistent magnetic characteristics, eliminating the influence of frequency-dependent magnetic properties and enabling accurate leakage current measurement across all drive frequencies including low frequencies
Solution Approach 2:
The invention changes the magnetic state of the core by applying a DC or low-frequency magnetizing current superimposed on the AC excitation current. This parameter change transforms the magnetic operating point of the core, stabilizing its magnetic characteristics and enabling precise measurement independent of the drive voltage frequency
2Measurement precision
If the power supply is completely stopped to carry out insulation deterioration diagnosis, then the measurement precision is improved, but the productivity deteriorates due to operational interruption
Solution Approach 1:
The magnetic core is preliminarily magnetized before detection to establish stable magnetic characteristics, enabling accurate insulation deterioration diagnosis to be performed during continuous operation without requiring power supply interruption
Solution Approach 2:
The invention enables continuous power supply during insulation deterioration diagnosis by stabilizing the magnetic core characteristics through preliminary magnetization. This allows the useful action of both power supply and detection to continue simultaneously without interruption, maintaining productivity while achieving accurate measurement
3Device complexity
If conventional current detection methods are used, then the device complexity is reduced, but the measurement precision deteriorates for minute leakage currents at low frequencies
Solution Approach 1:
A magnetizing current source is introduced to preliminarily magnetize the magnetic core before detection. This additional preliminary action stabilizes the magnetic characteristics, enabling precise detection of minute leakage currents at low frequencies while maintaining relatively simple device architecture
Solution Approach 2:
The magnetizing current acts as an intermediary that mediates between the power supply and the detection system. By stabilizing the magnetic core characteristics through this intermediary current, the system achieves high measurement precision for minute leakage currents without requiring complex detection apparatus
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 enables reliable and precise insulation deterioration diagnosis by reducing the dependency on drive frequency variations, enabling early detection and continuous operation without disrupting the load device's power supply.
Implementation Method 1
a magnetization control circuit for supplying an alternating current having a frequency at least twice as high as a drive frequency of the load device to the magnetizing coil to magnetize the magnetic core
Implementation Method 2
a zero-phase current transformer having an annular magnetic core, a magnetizing coil wound around the magnetic core, and a detecting coil wound around the magnetic core, the transformer being for detecting a zero-phase current of an electric path
Data Source
AI summary
The invention is related to an insulation deterioration diagnostic apparatus for an electric path connected between an inverter device and an inverter-driven load device, including: a zero-phase current transformer having an annular magnetic core, a magnetizing coil wound around the magnetic core, and a detecting coil wound around the magnetic core, the transformer being for detecting a zero-phase current of an electric path; a magnetization control circuit for supplying an alternating current having a frequency at least twice as high as a drive frequency of the load device to the magnetizing coil to magnetize the magnetic core; and a frequency extracting circuit for extracting a frequency component identical to the drive frequency fd, from the output signal of the detecting coil, whereby precisely measuring a current leaking from an inverter-driven load device over a wide range of frequencies.