Electrostatic Shield Openings for Cooler Rotating Machines

Solution Overview

Problem

Existing rotating electrical machines driven by power conversion circuits with inverters suffer from electrolytic corrosion of bearings due to switching operations, leading to reduced reliability. Additionally, conventional solutions that use electrostatic shields to reduce shaft voltage can cause heat to be trapped, resulting in demagnetization of permanent magnets and degradation of insulation performance.

Innovation Solution

A rotating electrical machine design that includes a rotor with embedded magnets, a stator with windings, bearings, and a casing connected to the stator core and bearings. An electrostatic shield with opening holes is integrated into the casing, allowing communication between the stator and rotor spaces to reduce shaft voltage and enhance cooling performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an electrostatic shield is disposed to close an opening of a slot of a stator to reduce shaft voltage, then shaft voltage is reduced and bearing corrosion is prevented, but heat generated in the rotor and stator stays in a narrow space causing demagnetization and insulation degradation

Engineering Contradiction:

Improvebearing reliabilityVSAvoidstator and rotor temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The electrostatic shield is segmented with multiple opening holes instead of being a continuous closed structure. This segmentation allows heat to pass through the shield while maintaining the electrostatic shielding function in the regions between openings, thus resolving the contradiction between shaft voltage reduction and heat dissipation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the electrostatic shield have different properties: some regions (with openings) allow heat passage, while other regions (between openings) maintain electrostatic shielding. This local differentiation enables the shield to simultaneously address both shaft voltage reduction and heat dissipation requirements.

Inventive Principle:

Principle #3Local quality

2Reliability

If an electrostatic shield is disposed to close an opening of a slot of a stator to reduce shaft voltage, then shaft voltage is reduced, but the performance of the rotating electrical machine is degraded due to heat-related issues

Engineering Contradiction:

Improveshaft voltage controlVSAvoidmachine performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The electrostatic shield is segmented with multiple opening holes instead of being a continuous closed structure. This segmentation allows heat to pass through the shield while maintaining the electrostatic shielding function in the regions between openings, thus resolving the contradiction between shaft voltage reduction and heat dissipation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the electrostatic shield have different properties: some regions (with openings) allow heat passage, while other regions (between openings) maintain electrostatic shielding. This local differentiation enables the shield to simultaneously address both shaft voltage reduction and heat dissipation requirements.

Inventive Principle:

Principle #3Local quality

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 proposed design effectively reduces shaft voltage and improves cooling performance, thereby enhancing the reliability and efficiency of the rotating electrical machine by preventing electrolytic corrosion and heat-related degradation issues.

Implementation Method 1

the conventional rotating electrical machine has been configured to reduce electrolytic corrosion by means of adjusting a stray capacitance distribution inside the rotating electrical machine with use of an electrostatic shield, so as to reduce a shaft voltage generated in the bearing

Methodology Applied

Scientific EffectElectrostatic shielding: Electrostatics

Implementation Method 2

the electrostatic shield has a plurality of opening holes by which a space in which the stator is disposed is communicated with a space in which the rotor is disposed

Methodology Applied

Scientific EffectThermal convection: Convection

Data Source

PatentUS12212189B2Rotating electrical machine

Publication Date: 2025.01.28 MITSUBISHI ELECTRIC CORP

AI summary

There are provided: a rotor including a rotating shaft and a rotor core; a stator including a stator core and stator windings; bearings; a casing fixed to the stator core and connected to the bearings, which houses the rotor and the stator; and an electrostatic shield connected to the casing. The electrostatic shield has a plurality of opening holes by which a space in which the stator is disposed is communicated with a space in which the rotor is disposed.