Loop Impedance Measurement Using Adaptive Frequency Selection
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Solution Overview
Problem
Existing methods for measuring loop impedance in electrical systems are plagued by uncertainties due to non-constant network voltage, irregular frequencies, and interference on conductors, leading to inaccurate measurements and the need for high currents that can trip protection devices and result in bulky measuring instruments.
Innovation Solution
An apparatus that generates a low current signal with an arbitrarily defined frequency band, minimizing interference by selecting a frequency free from network noise, allowing for precise phase-earth loop impedance measurement without tripping protection devices, using a compact and scalable circuit capable of measuring all types of loop impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high current is used for measurement, then measurement precision is improved, but protection devices are tripped and instrument size increases
Solution Approach 1:
The patent applies periodic action by using intermittent passive loads that are activated only during measurement intervals. The measurement system periodically applies test currents through the loop impedance being measured, allowing accurate measurements without continuous high current flow that would trip protection devices. This periodic measurement approach enables precise loop impedance determination while maintaining normal operation of protection devices between measurements.
Solution Approach 2:
The patent employs parameter changes by varying the measurement frequency and current amplitude dynamically. The system adapts the test current parameters based on the measured loop impedance values, using higher currents for high-impedance loops and lower currents for low-impedance loops. This adaptive parameter adjustment enables accurate measurements across different loop conditions without consistently using high currents that would trigger protection devices.
2Measurement precision
If high current is used for measurement, then measurement precision is improved, but instrument weight and dimensions increase
Solution Approach 1:
The patent uses periodic measurement cycles with intermittent high current pulses rather than continuous high current capability. The instrument only draws high measurement currents during brief measurement intervals, allowing the use of smaller, lighter power supply components and current generators that can handle peak currents temporarily but do not require the continuous high power capacity of traditional instruments.
Solution Approach 2:
The patent applies partial action by using just enough current to achieve accurate measurements for each specific loop condition. Rather than designing for maximum possible current capacity, the system dynamically adjusts the measurement current to the minimum necessary level for each measurement, reducing the size and weight of power handling components while maintaining measurement precision across different loop impedance ranges.
3Adaptability or versatility
If network voltage and frequency variations are present, then measurement adaptability is improved, but measurement precision deteriorates
Solution Approach 1:
The patent implements feedback mechanisms by continuously monitoring the actual network voltage and frequency during measurement and using this information to adjust the measurement parameters. The system measures the real-time network conditions and adapts the test current frequency and amplitude accordingly, compensating for voltage and frequency variations to maintain precise loop impedance measurements across different operating conditions.
Solution Approach 2:
The patent applies dynamics by making the measurement system adaptive and responsive to changing network conditions. The measurement frequency, current amplitude, and timing are dynamically adjusted based on real-time network voltage and frequency measurements, allowing the system to maintain measurement precision whether the network is stable or experiencing variations in voltage and frequency.
4Measurement precision
If intermittent passive load method is used, then phase-phase and phase-neutral impedance measurement is improved, but phase-earth impedance measurement becomes impossible
Solution Approach 1:
The patent achieves universality by designing a measurement system that can measure all three types of loop impedance (phase-phase, phase-neutral, and phase-earth) using a single integrated approach. The system uses a universal measurement circuit that can be configured to measure any loop type by simply changing the connection configuration, eliminating the need for separate measurement methods for different loop types and enabling phase-earth impedance measurement without tripping protection devices.
Data Source
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AI summary
An apparatus (10) for measuring loop impedance comprises a differential amplifier (1) suitable for conditioning a Vgen input signal, a controlled current generator (5) capable of making an Igen current signal flow between two measuring terminals A, B, and a microcontroller (6) set up for acquisition of the signals, for processing the signals and for controlling the current generator (5). The microcontroller (6) comprises a frequency selector (2), suitable for analysis of the Vgen signal for identifying frequencies which are free of network interference in such a way as to generate the Igen current signal at a frequency identified, a digital filter (3) suitable for extracting the component of Vgen derived from application of the Igen current signal, and processing means (4) suitable for supplying the impedance measurement.