Transformer Expansion Tank Liquid Seal for Pressure Equilibrium

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Solution Overview

Problem

Conventional liquid-immersed transformers require regular maintenance of flexible rubber bags or diaphragms in expansion tanks due to their limited lifespan, which is costly, dangerous, and disrupts electrical supply, and silica-gel desiccants are ineffective in maintaining low moisture content, leading to potential liquid exposure to air.

Innovation Solution

A preservation system with a separate chamber and u-shaped tube-like vessel using different liquids to separate gas from ambient air, eliminating the need for flexible parts, providing pressure control and sealing without maintenance, and using high-density liquids to prevent mixing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a flexible rubber bag or diaphragm is used in the expansion tank to separate gas from liquid, then the pressure cushion function is achieved, but the component has limited lifespan requiring regular maintenance

Engineering Contradiction:
Improvelifespan of separation componentVSAvoidmaintenance frequency
Core Design Contradiction:
ReliabilityVSEase of repair

Solution Approach 1:

The patent removes the flexible separation component (rubber bag or diaphragm) from the expansion tank system entirely. Instead, it uses a rigid tank structure with a liquid seal mechanism where a second liquid in a U-shaped tube separates the gas from ambient air, eliminating the need for flexible polymeric materials that require maintenance.

Inventive Principle:
Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a second liquid as an intermediary substance in a U-shaped tube to perform the separation function. This liquid acts as a mediator between the gas and ambient air, providing a maintenance-free alternative to flexible membranes while achieving the same pressure cushion and separation objectives.

Inventive Principle:
Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the transformer is located in remote locations or at elevated heights, then installation flexibility is improved, but maintenance becomes more dangerous and disruptive

Engineering Contradiction:
Improveinstallation location flexibilityVSAvoidmaintenance safety and disruption
Core Design Contradiction:
Adaptability or versatilityVSEase of operation

Solution Approach 1:

The patent designs a self-maintaining system where the rigid expansion tank with liquid seal requires no periodic intervention. The system serves itself by using gravity and density differences to maintain the liquid seal automatically, eliminating the need for human maintenance operations in dangerous or remote locations.

Inventive Principle:
Principle #25Self-service

3Difficulty of detecting and measuring

If silica-gel desiccant is used to reduce moisture content in the gas, then moisture control is attempted, but the desiccant is poorly effective and requires replacement

Engineering Contradiction:
Improvemoisture content controlVSAvoiddesiccant replacement frequency
Core Design Contradiction:
Difficulty of detecting and measuringVSEase of repair

Solution Approach 1:

The patent removes the silica-gel desiccant from the system entirely. By using a liquid seal with a second liquid that has high density and low volatility, the system inherently prevents moisture ingress without requiring desiccant materials that need monitoring and replacement.

Inventive Principle:
Principle #2Taking out (Extraction)

4Ease of repair

If a rigid expansion tank is used without flexible parts, then maintenance needs are reduced, but pressure equilibrium may be difficult to maintain

Engineering Contradiction:
Improvemaintenance requirementsVSAvoidpressure equilibrium
Core Design Contradiction:
Ease of repairVSStress or pressure

Solution Approach 1:

The patent uses hydraulic principles with a second liquid in a U-shaped tube to manage pressure equilibrium. The liquid column height adjusts automatically based on pressure differences, providing a passive pressure balancing mechanism that works seamlessly with the rigid tank structure without requiring flexible components.

Inventive Principle:
Principle #29Pneumatics and hydraulics

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

The system maintains pressure equilibrium without flexible parts, reducing maintenance needs and preventing liquid exposure, ensuring long-term operation with minimal disruption and chemical interaction risks.

Implementation Method 1

using high-density liquids to prevent mixing

Methodology Applied
Scientific EffectDensity difference: Density Gradient

Implementation Method 2

The gas acts as a pressure cushion for the variable volume of the liquid contained in the expansion tank

Methodology Applied
Scientific EffectCompressibility: Compression

Implementation Method 3

a u-shaped, tube-like vessel with a first upper part connected to the at least one chamber, a second upper part open to an environment, and a base part fluidically connecting the first upper part and the second upper part and being configured for holding a second liquid separating the gas from ambient air

Methodology Applied
Scientific EffectHydraulic seal: Liquid Membrane

Data Source

PatentEP4679463A1Preservation system for a liquid-immersed transformer and transformer system
Publication Date: 2026.01.14 HITACHI ENERGY LTD
  • EP4679463A1 patent drawingFigure 1A~1B
  • EP4679463A1 patent drawingFigure 1C~1D
  • EP4679463A1 patent drawingFigure 2

AI summary

The present disclosure relates to a preservation system (10) for a liquid-immersed transformer (30), comprising an expansion tank (11) configured for holding variable volumes of a first liquid (4) and a gas (18), respectively, at least one chamber (14) formed separate from the expansion tank (11) and configured for holding a further volume of the gas (18), the chamber (14) being fluidically connected to an upper part of the expansion tank (11), such that the gas (18) above the variable volume of the first liquid (4) can flow to and from the at least one chamber (14), and a u-shaped, tube-like vessel (16) with a first upper part (16a) connected to the at least one chamber (14), a second upper part open to an environment, and a base part (16b) fluidically connecting the first upper part (16a) and the second upper part and being configured for holding a second liquid (20) separating the gas (18) from ambient air. The present disclosure further relates to a transformer system (1).