Nonlinear Corona Shielding for Electrical Machines
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Solution Overview
Problem
High-voltage electrical machines face issues with partial discharges and insulation breakdown due to excessive field increases at the edges of laminated cores, leading to intense local heating and material degradation, while existing corona shielding systems either short-circuit or experience spark erosion due to inappropriate resistance levels.
Innovation Solution
A corona shielding system utilizing a nonlinear field strength-dependent electrical resistance material, shared between outer and overhang corona shielding, which adjusts resistance based on operating field strength to maintain a homogeneous electrical field distribution and prevent potential peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the outer corona shielding has low square resistance, then electrical conductivity is improved, but the laminated core can be electrically short-circuited leading to high induced circulating currents and high-current arcs
Solution Approach 1:
The patent applies a corona shielding material with nonlinear field strength-dependent electrical resistance, where the resistance dynamically adjusts based on the local electrical field strength. In regions of high field strength, the resistance decreases to prevent breakdown, while in regions of low field strength, the resistance remains high to prevent short-circuits and circulating currents. This dynamic parameter adjustment resolves the contradiction between needing high conductivity and avoiding harmful short-circuits.
2Reliability
If the outer corona shielding has high square resistance, then electrical insulation is improved, but high-voltage spark erosion can occur
Solution Approach 1:
The nonlinear field strength-dependent resistance of the corona shielding material automatically reduces resistance in regions of high electrical field strength, preventing spark erosion. In regions of low field strength, the material maintains high resistance for proper electrical insulation. This dynamic adaptation eliminates the need to choose between high insulation and spark erosion prevention, as both requirements are satisfied simultaneously through field-dependent resistance modulation.
3Ease of manufacture
If conventional linear resistance corona shielding material is used, then manufacturing is simplified, but severe nonlinearity is needed to force the electrical field out of regions of high field strengths
Solution Approach 1:
The patent employs a corona shielding material whose electrical resistance changes nonlinearly with field strength, enabling automatic field shaping without complex geometric configurations. This material property allows the system to achieve reliable field distribution control while maintaining relatively simple manufacturing, as the nonlinear resistance behavior inherently forces the electrical field out of high-field-strength regions without requiring precision-engineered shapes or multi-layer structures.
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 effectively reduces field strength increases, extends service life by preventing short-circuits and spark erosion, and ensures a balanced electrical field distribution through conductive and insulating properties adapted to varying field conditions.
Implementation Method 1
both the outer corona shielding and the overhang corona shielding are formed with the same corona shielding material which has a nonlinear field strength-dependent electrical resistance
Data Source
AI summary
The present disclosure relates to electrical machines. The teachings thereof may be embodied in a corona shielding system for an electrical machine. For example, a corona shielding system may include: an outer corona shield and an overhang corona shielding. The outer corona shielding and the overhang corona shielding may comprise a first corona shielding material having a nonlinear field strength-dependent electrical resistance.