Roebel Bar Insulation Transition Region Corona Shielding
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Solution Overview
Problem
The transition region between slot and yoke corona shielding in Roebel bars experiences excessive heating and discharges due to high capacitive coupling, leading to increased dielectric heat losses and surface discharges, particularly at higher voltages and with insulations having increased dielectric coupling.
Innovation Solution
A local thickening of the insulation in the transitional region is achieved by applying an additional insulation with lower insulating quality, such as resin-impregnated glass/mica strips or polymeric fibers, to reduce capacitive coupling, which can be implemented during production or subsequently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the insulating thickness is reduced to achieve higher insulating quality (En≥3.5 kV/mm), then the dielectric strength is improved, but the capacitive coupling increases leading to excessive heating and discharges
Solution Approach 1:
The patent applies different insulation qualities to different regions: high-quality insulation (En=2.5-3.0 kV/mm) in the slot part and yoke part, and lower-quality insulation (En<2.5 kV/mm) specifically in the transition region between SCS and YCS. This local differentiation reduces capacitive coupling where it causes problems while maintaining high dielectric strength where it is needed.
Solution Approach 2:
The patent changes the dielectric properties by introducing additional insulation with different material composition and thickness in the transition region. This modifies the capacitive coupling parameter locally, reducing the displacement currents and associated heat losses without affecting the overall insulating performance.
2Reliability
If additional insulation with lower insulating quality is applied in the transition region, then capacitive coupling is reduced preventing heating and discharges, but the device complexity increases
Solution Approach 1:
The insulation system is segmented into distinct regions: standard insulation in the slot and yoke parts, and additional transition-region insulation specifically at the SCS/YCS boundary. This segmentation targets the problem area precisely without unnecessarily complicating the entire insulation system.
Solution Approach 2:
The additional insulation acts as an intermediary element between the SCS and YCS regions, mediating the transition and reducing the harmful capacitive coupling. It serves as a buffer zone that prevents direct high-stress interaction between the low-resistance SCS and high-impedance YCS.
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 approach effectively reduces capacitive coupling by a factor of 3, preventing excessive heating and discharges in the transitional region, thereby enhancing the reliability of Roebel bars in high-voltage applications.
Implementation Method 1
the capacitive coupling via the insulation gains in significance
Implementation Method 2
the dielectric heat losses, which are proportional to E*j
Implementation Method 3
the surface of this insulation is usually provided with a conductive layer... as corona shielding
Implementation Method 4
with a semiconductive layer, which preferably has a field-dependent conductivity
Data Source
AI summary
A Roebel bar for a rotating electrical machine includes a straight slot part disposed in a slot in an iron sheet of a stator of the rotating electrical machine and a bent yoke part adjacent to the straight slot part and protruding from the stator, wherein the bent yoke part is configured to connect the Roebel bar to at least one more Roebel bar so as to form a winding. A copper conductor disposed in the straight slot part and the bent yoke part is surrounded by an insulation having an outer surface. A slot corona shielding includes an electrically conductive layer disposed on the outer surface of the insulation in an area of the straight slot part. A yoke corona shielding includes a semiconducting layer disposed on the outer surface of the insulation in an area of the bent yoke part.