Oil-Filled Power Bushing Bellow Pressure Compensation
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Solution Overview
Problem
Standard oil-filled power bushings experience gas bubble formation due to thermal changes, leading to partial discharges and accelerated aging, and existing solutions like movable pistons and sealed bellows face issues with tightness, friction, and overpressure, compromising the integrity of the bushing.
Innovation Solution
A liquid-filled power bushing with a bellow completely immersed in the expansion chamber, allowing the bellow's interior chamber to communicate with the external atmosphere through a channel or orifice, preventing gas contact with the insulating liquid and enabling expansion and contraction without gas formation within the oil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a gas cushion is used in the oil expansion chamber to compensate thermal expansion, then the oil can expand and contract with temperature variations, but gas bubbles form when N2 is released from the oil during sudden temperature drops, causing partial discharges and insulation degradation
Solution Approach 1:
The invention divides the expansion chamber into two separate compartments: one for oil expansion and another for gas cushion. This segmentation prevents direct contact between the insulating oil and the gas cushion, eliminating the harmful effect of gas bubbles forming in the oil during temperature variations while maintaining the beneficial thermal expansion compensation function
Solution Approach 2:
The patent introduces an intermediary structure (the partition wall with communication hole and/or bellow) between the oil and gas cushion. This intermediary allows the gas cushion to compensate for thermal expansion while preventing direct gas-oil contact that would cause bubble formation and partial discharges
2Object-affected harmful factors
If a movable piston is used to separate oil and gas in the expansion chamber, then gas bubbles are prevented from forming in the liquid, but tightness issues and friction occur at the interfaces between the piston and conductor and piston and walls
Solution Approach 1:
The invention extracts the harmful friction and tightness problems by replacing the movable piston with a fixed partition wall or bellow structure. This eliminates the sliding interfaces that cause friction and potential leakage, while still achieving complete separation between oil and gas compartments
Solution Approach 2:
The patent replaces the mechanical sliding piston system with a stationary partition wall or elastic bellow structure. This substitution eliminates the need for sliding contacts, removing the associated friction and tightness issues while maintaining effective oil-gas separation
3Stress or pressure
If sealed bellows are used to compensate oil expansion, then the bellows contract or dilate with liquid volume changes to avoid overpressure, but the bellows must withstand high overpressure generated during liquid expansion
Solution Approach 1:
The invention segments the expansion chamber into separate oil and gas compartments, allowing the gas cushion to independently absorb pressure variations. This eliminates the need for bellows to withstand high overpressure, as the gas cushion naturally accommodates volume changes without requiring high pressure resistance
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 solution effectively prevents gas bubble generation, reduces manufacturing costs, and maintains a pressure close to atmospheric pressure, enhancing the bushing's reliability and longevity by allowing it to 'breathe' and preventing overpressure risks.
Implementation Method 1
The bellow according to the invention further comprises a channel or orifice making its interior chamber communicating with a space located outside from the bushing, typically outside from the expansion chamber, so that gas may enter said interior chamber from said space when the volume of the interior chamber increases and may be released from the interior chamber into said space when the volume of the interior chamber decreases
Implementation Method 2
the solubility of the gas in the oil increases with increasing temperature. Consequently, N2 is dissolved in the oil until the oil-gas system reaches an equilibrium corresponding to an N2 saturation level in the oil of 100%. In case of sudden temperature drop (load reduction and/or external cooling), N2 solubility in the oil decreases
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
Oil filled power bushing with pressure compensation by bellow. The present invention concerns a liquid filled power bushing (1) comprising: - an insulator (11) comprising an insulator chamber (111) for receiving an insulating liquid (2); - an expansion chamber (14) communicating with the insulator chamber (111) for enabling an expansion or contraction of the insulating liquid (2); - an electrical conductor (13) located within the bushing (1) and extending through the expansion chamber (14) and the insulator chamber (111); characterized in that it further comprises a bellow (3) located inside the expansion chamber (14), the bellow (3) comprising an interior chamber (31) with variable volume, said interior chamber (31) communicating via a channel (32) with a space (4) filled with gas and located outside the expansion chamber (14) for enabling said gas to enter the interior chamber (31) in case of an expansion of the volume of the interior chamber (31) resulting from the contraction of the insulating liquid (2) and being released from said interior chamber (31) into said space in case of a contraction of the volume of the interior chamber (31) resulting from the expansion of the insulating liquid (2).