HVDC Transformer Insulating Liquid Resistivity Control
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Solution Overview
Problem
In High Voltage Direct Current (HVDC) environments, transformers experience excessive electrical DC stress due to the high resistivity of Gas-to-Liquid (GTL) oil, which shifts the electric field to dielectrically weaker liquid insulation, leading to adverse effects on the insulation system.
Innovation Solution
A blend of a high-resistivity gas-to-liquid oil with a second oil or additive, such as mineral oil or synthetic ester, is used to adjust the equilibrium resistivity of the insulating liquid, ensuring it remains at least 10^11 ohm-meters but no more than half the value of the primary oil's resistivity, thereby reducing stress on the liquid insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the resistivity of the insulating liquid is increased, then the dielectric strength is improved, but the DC electric field shifts to the liquid causing excessive stress on the insulation system
Solution Approach 1:
The patent optimizes the resistivity parameter to a specific range by controlling the blend ratio of GTL oil and mineral oil or by selecting appropriate additives. This ensures the liquid insulation has sufficient dielectric strength while maintaining resistivity low enough to prevent excessive DC field stress concentration.
2Duration of action of stationary object
If mineral oil with additives is used, then the high temperature operating stability is improved, but the resistivity decreases which may shift stress to the liquid insulation
Solution Approach 1:
The patent carefully controls the type and concentration of additives (0.001-1% by weight) to achieve the desired balance between thermal stability and resistivity. By selecting specific additives and optimizing their concentrations, the patent maintains adequate resistivity levels while still benefiting from the high-temperature stability that additives provide.
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 solution effectively lowers the resistivity of the insulating liquid, reducing stress and improving the reliability and safety of inductive devices by ensuring the liquid insulation can withstand electrical DC fields, while maintaining a favorable resistivity ratio with solid insulation, thus optimizing insulation performance.
Implementation Method 1
a blend of a high-resistivity gas-to-liquid oil with a second oil or additive
Implementation Method 2
the resistivity of the oil is an important factor
Implementation Method 3
Transformers that experience strong electrical DC potential fields are subjected to DC stress
Implementation Method 4
The dielectric insulation in converter transformers usually comprises liquid insulation
Data Source
Figure 1~2
AI summary
The present disclosure relates to an insulating liquid (26) for an enclosure (24) intended to enclose an inductive device comprising a winding (20) surrounded by solid insulation (22) as well as to an inductive arrangement comprising a container (24) with such an inductive device (12) and insulating liquid (26). The insulating liquid (26) comprises a first main component in the form of a first oil having an equilibrium resistivity of at least 1013 ohm metres and at least one second auxiliary component in the form of a second oil or additive having a lower equilibrium resistivity causing the equilibrium resistivity of the insulating liquid to be at least 1011 ohm metres and at most half the value of the equilibrium resistivity of the first oil when in use in the enclosure.