Differential Protection Device Filtering Excitation Carrier Signal
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Solution Overview
Problem
Existing differential protection devices struggle to accurately detect direct current fault currents due to interference from alternating current components, leading to potential overmodulation and unjustified triggering.
Innovation Solution
Incorporating a low-pass or band-pass filtering circuit as the first stage in the operational chain to extract the excitation carrier signal component from the fault signal, combined with a rectifier averaging circuit to linearize the DC current measurement and a comparator for controlled triggering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the excitation signal is transmitted through the transformer winding to detect insulation faults, then the sensitivity to insulation resistance changes is improved, but the carrier signal causes unwanted electromagnetic radiation and interference with other transformers
Solution Approach 1:
The patent introduces a modulator as an intermediary device that converts the low-frequency excitation signal into a high-frequency modulated carrier signal for transmission through the transformer winding. This mediator allows the detection function to operate effectively while the high-frequency carrier minimizes electromagnetic radiation and interference with other transformers, thus resolving the contradiction between detection sensitivity and electromagnetic interference.
2Object-generated harmful factors
If a high-frequency carrier is used to reduce electromagnetic radiation, then the interference with other transformers is reduced, but the detection of insulation faults becomes more difficult due to signal attenuation
Solution Approach 1:
The patent employs a feedback mechanism where the response signal from the transformer winding is demodulated and compared with the original excitation signal. The system continuously monitors the insulation resistance based on the phase and amplitude changes of the response signal, providing real-time feedback to maintain accurate detection despite signal attenuation at high frequencies. This feedback loop ensures that insulation faults can be detected even when using a high-frequency carrier to minimize electromagnetic interference.
3Speed
If the excitation frequency is increased to improve detection speed, then the response time is reduced, but the signal becomes more susceptible to noise and interference
Solution Approach 1:
The patent uses periodic modulation of the excitation signal at a specific carrier frequency to improve detection speed. By modulating the excitation signal periodically and detecting the corresponding periodic response, the system achieves fast response times while the periodic nature of the signal allows for easier filtering and noise rejection through synchronous detection techniques, thus resolving the contradiction between detection speed and noise susceptibility.
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
Ensures precise detection of DC fault currents even with AC interference, preventing unnecessary tripping and maintaining reliable safety by linearizing the measurement and controlling triggering levels.
Implementation Method 1
When a periodic excitation signal is applied to the winding of a transformer, voltage peaks occur at certain frequencies depending on the winding and the circuit connected to the transformer terminals
Implementation Method 2
A band-pass filter is provided having a pass-band including the fundamental frequency and a reject-band including at least one harmonic frequency
Data Source
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AI summary
The subject of the present invention is a differential protection device (1) allowing fault currents in an electrical installation to be detected and comprising a detection and control module (3) with a measurement torus (4) through which the conductors (2, 2', 2'') of the network pass, an excitation circuit (15) and a measurement coil (5) capable of and designed for generating a fault signal (SD') that is connected to circuits (7, 8, 9) for processing and evaluating the fault signal (SD') and transmitting a control signal (SC) for a cut-off means (11), which are arranged to form an operational electronic chain (14). Device (1) characterized in that said operational chain (14) of said module (3) comprises a low-pass or band-pass filtering circuit (9), constituting the first circuit of said chain (14) and processing the fault signal (SD') so as to extract the signal component substantially corresponding to the excitation carrier (SPE) therefrom.