Active Monitoring for High Voltage Bushing Insulation
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Solution Overview
Problem
Current on-line transformer monitoring systems are limited in measuring capacitance and power factor values for both the inner and outer condenser sections of energized bushings, as well as transformer windings, due to passive sensor limitations that only measure power frequency current through the inner section, failing to monitor the outer section and neutral bushings effectively.
Innovation Solution
An active monitoring system that injects a high frequency voltage into the test tap of the bushing, using an active sensor with a high pass filter to separate the electrical circuit into high frequency and power frequency buses, allowing for the measurement of current magnitude and phase angle, enabling the determination of capacitance and power factor values for both inner and outer condenser sections, as well as transformer windings, even when the bushing is energized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive sensor is used to monitor bushing capacitance and power factor, then the system can provide continuous monitoring, but it can only measure the inner condenser section and not the outer condenser section or transformer windings
Solution Approach 1:
The patent changes the frequency parameter by injecting high frequency voltage signals (e.g., 100 kHz) into the bushing test tap. This frequency change enables the measurement system to penetrate through the inner condenser section and measure the outer condenser section capacitance and transformer winding capacitances, which are inaccessible to power frequency passive sensors. The high frequency injection transforms the measurement capability from partial to complete bushing monitoring.
2Loss of information
If an active monitoring system injects high frequency voltage into the test tap, then complete measurement of bushing and transformer insulation components is enabled, but the system complexity increases due to additional injection circuitry and signal separation requirements
Solution Approach 1:
The patent introduces a high pass filter as an intermediary component that separates the high frequency measurement signal from the power frequency operating voltage. This filter acts as a mediator that allows the high frequency injection signal to pass through to the measurement circuit while blocking the power frequency voltage, thereby simplifying the overall system design by providing clean signal separation without requiring complex isolation circuits.
Solution Approach 2:
The monitoring system is segmented into distinct functional modules: a high frequency voltage injection circuit, a high pass filter for signal separation, and a measurement circuit for capacitance and power factor determination. This segmentation allows each module to be optimized independently and simplifies the overall system architecture, making the complex measurement task manageable through modular design.
3Reliability
If high frequency voltage is injected into the test tap to measure outer condenser section capacitance, then complete on-line testing is achieved, but the risk of interference with the energized bushing operation increases
Solution Approach 1:
The high frequency voltage injection is implemented as a periodic superimposed signal on top of the continuous power frequency operating voltage. This periodic injection occurs at high frequency (e.g., 100 kHz) cycles, allowing the measurement system to extract capacitance information through the regular high frequency signal while the underlying power frequency voltage continues to drive the bushing operation, thereby minimizing operational interference.
Solution Approach 2:
The high frequency voltage injection creates electrical oscillations at high frequency that propagate through the bushing insulation components. These oscillations are analogous to mechanical vibrations in that they are high frequency disturbances that do not affect the lower frequency operating conditions, allowing measurement without disrupting the energized bushing's normal operation at power frequency.
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
Enables complete on-line testing of bushing and transformer insulation components, accurately measuring capacitance and power factor for both C1 and C2 sections of phase and neutral bushings, and self and mutual capacitances of transformer windings, reducing the risk of catastrophic failures and equipment damage.
Implementation Method 1
using an active sensor with a high pass filter to separate the electrical circuit into high frequency and power frequency buses
Implementation Method 2
measuring a current magnitude and a phase angle of a high frequency current produced by the 1 kHz or more voltage passing through the condenser sections of the bushing
Data Source
AI summary
Systems and methods for measuring the integrity of insulation components in electrical systems. In preferred embodiments, an active sensor is coupled to a test tap of a bushing, the active sensor having an electrical circuit electrically coupled to the test tap, and wherein the electrical circuit includes a high pass filter that divides the electrical circuit into a high frequency bus and a power frequency bus. A grounded high frequency voltage is injected into the test tap via the frequency bus circuit. Resulting voltages and currents may be measured and compared to a reference voltage to determine capacitances and power factors for both the inner and outer sections of the bushing. Once the capacitances and power factors of the bushings are known, grounded and ungrounded high frequency voltages may be injected to determine capacitances and power factors of a connected transformer or reactor.