Mono-Tore Loop Ohmmeter Compensation for DC Leakage Flux
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Solution Overview
Problem
Existing loop ohmmeters face inaccuracies in measuring loop impedance due to magnetic flux losses and variations in iron and copper losses, which are influenced by parasitic AC and DC currents, necessitating compensation to maintain measurement accuracy.
Innovation Solution
A single-core loop ohmmeter uses a secondary winding to measure parasitic induction from a DC leakage current, compensating for its influence by injecting a constant current opposite and proportional to the parasitic induction, using a method involving a second secondary winding, integrator, comparator, and low-pass filter, with digital or analog processing to ensure accurate impedance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single transformer is used for both voltage injection and current measurement, then device complexity is reduced, but measurement precision deteriorates due to magnetic flux losses and iron losses
Solution Approach 1:
The patent segments the transformer into two independent secondary windings: one for current measurement and another for measuring magnetic flux losses. This allows separate measurement of the loop current and the transformer's magnetic losses, enabling compensation to improve measurement precision while maintaining the simple single-transformer structure.
Solution Approach 2:
The patent introduces a compensating current as an intermediary element. This compensating current, injected into the primary winding, counteracts the magnetic flux losses measured by the second secondary winding, thereby eliminating the source of measurement error and improving precision without adding complex external equipment.
2Measurement precision
If measurement current is used to generate alternating induction, then loop impedance can be measured, but DC leakage current causes parasitic induction that deteriorates measurement precision
Solution Approach 1:
The patent implements a feedback mechanism where the second secondary winding continuously measures the magnetic flux losses caused by DC leakage current, and this measurement is used to generate a compensating signal that is fed back to the primary winding to cancel the parasitic induction, thereby maintaining measurement precision.
Solution Approach 2:
The patent converts the harmful parasitic induction from DC leakage current into a useful measurement signal. By using the second secondary winding to measure the flux losses caused by the DC leakage, the system transforms the harmful effect into information that can be used to generate a compensating current, thereby eliminating the harm and improving measurement accuracy.
3Measurement precision
If iron losses and copper losses are compensated, then measurement accuracy is improved, but device complexity increases due to additional windings and processing circuits
Solution Approach 1:
The patent makes the single transformer multi-functional by equipping it with two secondary windings: one for current measurement and another for measuring magnetic flux losses. This allows the same transformer to perform both measurement functions and enable loss compensation without requiring separate measurement devices, thereby improving precision while limiting the increase in overall device complexity.
Solution Approach 2:
The patent merges the voltage injection function, current measurement function, and magnetic loss measurement function into a single transformer assembly. By combining these functions in one device, the patent achieves comprehensive measurement and compensation capabilities while avoiding the complexity of multiple separate devices and their interconnections.
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 method effectively reduces the impact of DC leakage currents on iron losses, ensuring precise loop impedance measurements without disrupting the measurement current, allowing continuous monitoring and remote transmission of impedance data.
Implementation Method 1
one transformer consisting of a toroid with a primary winding Np, used simultaneously for the injection of the voltage and the measurement of the current flowing in the earth loop, and a secondary winding Ns with a single turn formed by the earth connection conductor
Implementation Method 2
the measurement of the parasitic induction is derived from an output voltage Ub delivered across the terminals of a second secondary winding of Na turns of the single transformer
Data Source
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Figure 6~7
AI summary
Single-core ohmmeter for measuring a loop impedance Zx, comprising a single transformer having a primary winding of Np turns (14) and a secondary winding of a single turn (16) forming a measuring loop of impedance Zx, in which to compensate for a parasitic induction produced by a DC leakage current flowing in the measuring loop without canceling a measuring current Ip generating an alternating induction of constant average value for the measurement of the loop impedance Zx, the transformer comprises a second secondary winding of Na turns (18) whose output voltage Ub is delivered to a processing module (30 - 40) providing a voltage intended to be added to an alternating measuring voltage Vp in an adder (22) delivering the current to be injected into the primary winding (14) after passing through a voltage-current converter (20) supplying current to the primary winding via a shunt resistor (19).