Three-Layer End Winding Corona Protection for High-Voltage Machines
Solution Overview
Problem
Existing end winding corona protection designs for high-voltage rotating machines are inadequate in controlling voltage drops and surface currents caused by power converter-driven pulses, leading to potential discharges and erosion, especially in asynchronous machines with steel-supported windings under high mechanical stress.
Innovation Solution
A three-layer end winding corona protection system comprising a highly conductive inner layer, a semiconductive middle layer, and a medium resistive outer layer, applied as tapes or paint, with specific surface resistance ranges to manage voltage differences, currents, and mechanical abrasion, ensuring surface currents flow through the stator core and not through metallic bolts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional two-layer end winding corona protection is used, then the machine operates safely under sinusoidal voltages, but the voltage drops and surface currents caused by power converter-driven pulses cannot be controlled, leading to discharges and erosion
Solution Approach 1:
The corona protection is divided into three distinct layers with different resistance characteristics: an innermost layer of low surface resistance (10-200 Ω) to handle high dv/dt pulses, an intermediate layer of medium surface resistance (100-10000 Ω) for current control, and an outermost layer of high surface resistance (>10000 Ω) for protection. This segmentation allows each layer to address specific aspects of the harmful effects from power converter pulses.
Solution Approach 2:
The corona protection uses a composite structure combining materials with different electrical properties in three layers. The innermost layer uses highly conductive material to shunt displacement currents during voltage transients, the intermediate layer uses semiconductive material for controlled current flow, and the outermost layer uses resistive material for protection against erosion and discharge.
2Reliability
If the end winding corona protection is made thicker to improve protection effectiveness, then better control of voltage drops and surface currents is achieved, but the space requirements for winding assembly are exceeded
Solution Approach 1:
Each layer is optimized with specific local properties: the innermost layer has very low resistance (10-200 Ω) to handle high dv/dt pulses effectively, the intermediate layer has medium resistance (100-10000 Ω) for current control, and the outermost layer has high resistance (>10000 Ω) for protection. This local optimization allows thin layers to achieve maximum protection effectiveness.
Solution Approach 2:
The invention changes the resistance parameter distribution across three thin layers rather than using a single thick layer. By optimizing the resistance values and thickness of each layer, the total thickness is minimized while maintaining effective corona protection against power converter pulses.
3Strength
If steel materials are used for mechanical support of the rotor winding, then the high mechanical stress from centrifugal forces and vibrations is withstand, but the electric conductivity of the support materials causes new electric issues in the end winding area
Solution Approach 1:
The three-layer corona protection structure acts as an intermediary between the steel support structure and the end winding. The innermost layer provides a low-resistance path that directs surface currents away from the steel bolts, preventing contact arcing while the steel structure provides mechanical support.
Solution Approach 2:
The harmful electric currents are extracted from the steel support structure by providing an alternative low-resistance path through the innermost corona protection layer. This prevents the currents from flowing through the steel bolts and causing contact arcing and erosion.
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
Effectively controls voltage drops and prevents discharges, maintaining safe operation under high voltages and currents, while being thin enough for assembly and suitable for asynchronous machines with steel-supported windings, supporting currents up to 3 kA and voltages up to 4-5 kV.
Implementation Method 1
The innermost layer has a surface resistance in the range of 10 Ω to 200 Ω and is designed to control voltage differences which occur along the surface of the end winding
Implementation Method 2
The intermediate layer has a resistance perpendicular to its surface in the range of 100 MΩ/mm2 to 106 MΩ/mm2 and is designed to limit currents perpendicular to the surface of the end winding corona protection
Implementation Method 3
The outermost layer has a surface resistance in the range of 1 kΩ to 10 kΩ and is designed to limit voltage gradients on an outermost surface of the end winding corona protection and to protect against mechanical abrasion
Implementation Method 4
Both the end winding corona protection and the slot corona protection are designed to control surface currents in a way that no visible discharges (corona, arcing) occur
Data Source
AI summary
An end winding corona protection. A winding of a rotating electric machine, comprising a conductor and a groundwall insulation surrounding the conductor, an end winding corona protection arranged on the outer surface of the ground-wall insulation, the end winding corona protection comprising a first layer characterized in that the surface resistance of the first layer is in the range of 10 Ohm to 80 Ohm, and in that the end winding corona protection further comprises a second layer arranged on the outer surface of the first layer, wherein the second layer is made of semiconductive material, and wherein third layer is arranged on the outer surface of the second layer and made of medium resistive material.