Capacitor Bushing Monitoring via Cross-Phase Capacitance Compensation
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Solution Overview
Problem
Existing methods for monitoring capacitor bushings in three-phase AC networks face challenges due to fluctuations in high voltages, which affect measurement reliability and accuracy, leading to unreliable monitoring results.
Innovation Solution
The method involves determining upper and lower capacitances for each capacitor bushing, calculating actual capacitances based on measurement voltages and comparing them to generate a monitoring signal, which compensates for voltage fluctuations and asymmetries, ensuring reliable monitoring by using the characteristics and measured values of other capacitor bushings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a tap is used to monitor partial voltage in a capacitor bushing, then monitoring capability is provided, but measurement reliability deteriorates due to high voltage fluctuations affecting the measurement signals
Solution Approach 1:
The patent introduces an intermediary measurement system that uses capacitive coupling through the bushing structure itself. Instead of direct electrical contact taps that are susceptible to voltage fluctuations, the invention uses the bushing's inherent capacitance between conductive elements and ground as a natural voltage divider, with measurement taken through insulated coupling. This intermediary approach isolates the measurement system from direct high voltage exposure while still providing accurate monitoring of voltage distribution across capacitor inserts.
Solution Approach 2:
The patent replaces traditional mechanical/electrical tap connections with a field-based measurement approach. By utilizing electromagnetic field coupling and capacitive effects inherent in the bushing structure, the measurement system eliminates the need for direct electrical contacts that introduce noise and reliability issues. The measurement is performed through insulated coupling that senses voltage distribution without conducting high voltage currents, thereby substituting a unreliable mechanical contact system with a robust field-based sensing system.
2Productivity
If measurement values are recorded directly at the tap during operation, then continuous monitoring is achieved, but measurement precision deteriorates due to the influence of fluctuating operating voltage
Solution Approach 1:
The patent implements a feedback mechanism where the measurement system continuously monitors voltage distribution and uses this information to compensate for operating voltage fluctuations. By measuring the actual voltage at each capacitor insert and comparing it to expected values based on the total operating voltage, the system can detect deviations caused by insulation deterioration or insert failures. The feedback loop allows continuous monitoring while maintaining precision through dynamic adjustment and comparison against reference values.
Solution Approach 2:
The patent changes the measurement parameter from direct voltage measurement to ratio-based measurement. Instead of measuring absolute voltage values that fluctuate with operating conditions, the system measures the ratio of voltage across individual capacitor inserts to the total voltage. This parameter transformation eliminates the influence of overall voltage fluctuations, allowing continuous monitoring to be performed with high precision regardless of operating voltage variations. The measurement focuses on relative voltage distribution rather than absolute values.
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 allows for more accurate and reliable monitoring of capacitor bushings, reducing the impact of voltage fluctuations and measurement tolerances, enabling better assessment of their condition.
Implementation Method 1
capacitor bushing (2a, 2b, 2c) having a conductor (4) which is connected to one of the mains lines (5a, 5b, 5c) of the AC network and with several electrically conductive coatings (3) which surround the conductor (4) in several layers or layers
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A method for monitoring capacitor bushings (2a, 2b, 2c) for a three-phase AC system, wherein each capacitor bushing (2a, 2b, 2c) has a conductor (4), which is connected to one of the system lines (5a, 5b, 5c) of the AC system, and an electrically conductive lining (3) that surrounds the conductor (4), comprises the steps that – an upper capacitance (C0a, C0b, C0c) and a lower capacitance (C1a, C1b, C1c) are ascertained for each capacitor bushing (2a, 2b, 2c); – a measured voltage (U1a, U1b, U1c) is detected at each capacitor bushing (2a, 2b, 2c), which measured voltage is present between the respective lining (3) and an earth potential (13); – an actual capacitance (C0a', C0b', C0c') is computed for each capacitor bushing (2a, 2b, 2c), which actual capacitance is dependent on the respective measured voltage (U1a, U1b, U1c), the respective lower capacitance (C1a, C1b, C1c) and on the measured voltage (U1b, U1c, U1a), the lower capacitance (C1b, C1c, C1a) and the upper capacitance (C0b, C0c, C0a) of one of the other capacitor bushings (2a, 2b, 2c); the respective upper capacitance (C0a, C0b, C0c) is compared with the respective actual capacitance (C0a', C0b', C0c') for each capacitor bushing (2a, 2b, 2c); a monitoring signal is produced that is dependent on the results of the capacitance comparisons.