Dry Transformer Active Part With Composite Bobbin
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Solution Overview
Problem
High electrical stress in dry insulated transformers, particularly at the HV winding edges, hinders the reduction of size and weight, and existing solutions do not effectively manage this stress to achieve compact designs comparable to oil-insulated transformers.
Innovation Solution
The active part of the dry-type distribution transformer employs a composite bobbin with higher permittivity than the surrounding insulation, combined with metallization and a resistive layer on the HV coil winding, along with an air gap between LV and HV coils to control electric fields, allowing for a more compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the coil is wound into a bobbin with higher permittivity than the surrounding insulation, then the electrical stress at the winding edges is reduced and the transformer size is decreased, but the manufacturing complexity increases
Solution Approach 1:
The bobbin is constructed as a composite structure combining multiple materials with different permittivities - a core material with higher permittivity than the surrounding insulation, and optionally additional layers or components. This composite design allows precise control of the electric field distribution to reduce electrical stress at the winding edges while maintaining manufacturability through modular construction
Solution Approach 2:
The permittivity distribution in the bobbin is optimized locally - the material directly surrounding the winding edges has higher permittivity to concentrate the electric field in that specific region, while other parts of the bobbin may have different permittivity values. This localized property variation reduces overall electrical stress without requiring the entire bobbin to be complex
2Strength
If the bobbin wall thickness is increased to provide better support, then the mechanical strength is improved, but the transformer size and weight increase
Solution Approach 1:
The bobbin utilizes composite materials with high strength-to-weight ratio, combining materials that provide both mechanical support and electrical field control functions. This allows adequate wall thickness for strength while minimizing unnecessary material that would increase weight
Solution Approach 2:
The bobbin structure serves multiple functions simultaneously: it provides mechanical support for the windings, controls the electric field distribution through its permittivity characteristics, and offers insulation. This multi-functionality reduces the need for additional separate components that would increase weight
3Stress or pressure
If the permittivity of the bobbin material is increased to control the electric field, then the electrical stress distribution is improved, but the cost of materials increases
Solution Approach 1:
High permittivity material is applied only in the specific regions where electric field control is most critical - particularly at the winding edges where electrical stress is highest. Other regions of the bobbin may use lower permittivity or standard insulation materials, reducing overall material cost while maintaining electrical performance
Solution Approach 2:
The bobbin employs a composite structure where high permittivity material is combined with more cost-effective standard insulation materials. This stratified approach ensures optimal electrical stress control at critical interfaces while minimizing the use of expensive materials throughout the entire structure
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 reduces electrical stress, enabling a more compact and cost-effective design by minimizing size, weight, and material usage while maintaining comparable electrical parameters to oil-insulated transformers.
Implementation Method 1
winding the coil into a bobbin with permittivity higher than the permittivity of the surrounding insulation. This moves the high electrical field away from the winding edges and into the solid insulation
Implementation Method 2
The resistive layer 7 forms a shield for control an electric fields around the limb 3 and LV and HV coils
Implementation Method 3
Between the external surface of the metallic layer placed on the frontal face of the insulating body and an internal surface of the yoke, an air gap is situated which is free of an electric field generated by LV coils and HV coils
Data Source
Figure 1~2
Figure 3
AI summary
The present invention relates to an active part of a dry-type distribution transformer having an insulation system with electrical field control. An active part of the dry transformer comprising a core (1) with yokes (2) and limbs (3) having an a longitudinal axis (A) around which LV coils (4) and winding bobbin (5) is placed concentrically. The bobbin (5) has a shape of a longitudinal cylinder (5a) which is ended with annular discs (5b). The bobbin (5) is made of material having a dielectric permittivity which is two to five times higher more the dielectric permittivity of the insulating body (8) surrounding the limb (3) around the axis (A), in which the LV coils (4) and HV coils (6) are embedded. The external facial surfaces of the insulating body (8) is provided with a metallic layer (10) having such electric conductivity that the part of the insulating body (8) between an internal surface of the metallic layer (10) and an external surface of the annular disc (5b) has a thickness (d3) which is sufficient for insulation. A side surface of the cylinder (5a) is covered with a resistive layer (7) being a control shield of an electric field around the limb (3) of the core (1) and the HV coils (6) and the LV coils (4).