Induction Motor Rotor Bars with Radial Resistivity Gradient

Solution Overview

Problem

Existing electric induction motors and synchronous motors with traditional high resistivity rotors suffer from poor efficiency and inadequate starting torque characteristics, necessitating an improvement in rotor design to enhance both efficiency and starting torque.

Innovation Solution

The design incorporates conducting elements with a resistivity profile that decreases either continuously or in steps from the rotor axis, utilizing materials like copper and zinc alloys, particularly in rotor bars for squirrel cage induction motors and pole shoes for solid salient pole synchronous motors, manufactured using additive manufacturing to optimize starting characteristics and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If high-resistivity material (aluminium) is used in rotor bars, then starting torque is improved, but efficiency deteriorates

Engineering Contradiction:

Improvestarting torqueVSAvoidefficiency

Core Design Contradiction:

ForceVSLoss of energy

Solution Approach 1:

The rotor bar is divided into two distinct zones with different material properties: an outer zone with high resistivity material (aluminium) for improved starting torque, and an inner zone with low resistivity material (copper) for reduced losses and improved efficiency during steady-state operation. This local differentiation of material properties allows simultaneous optimization of both starting characteristics and running efficiency.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The rotor bar employs a composite structure combining two different conductive materials - aluminium in the outer region and copper in the inner region. This composite material approach leverages the advantageous properties of each material: aluminium's high resistivity for starting torque enhancement and copper's low resistivity for efficiency improvement during normal operation.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If low-resistivity material (copper) is used in rotor bars, then efficiency is improved, but starting torque deteriorates

Engineering Contradiction:

ImproveefficiencyVSAvoidstarting torque

Core Design Contradiction:

Loss of energyVSForce

Solution Approach 1:

The rotor bar is divided into two distinct zones with different material properties: an outer zone with high resistivity material (aluminium) for improved starting torque, and an inner zone with low resistivity material (copper) for reduced losses and improved efficiency during steady-state operation. This local differentiation of material properties allows simultaneous optimization of both starting characteristics and running efficiency.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The rotor bar employs a composite structure combining two different conductive materials - aluminium in the outer region and copper in the inner region. This composite material approach leverages the advantageous properties of each material: aluminium's high resistivity for starting torque enhancement and copper's low resistivity for efficiency improvement during normal operation.

Inventive Principle:

Principle #40Composite materials

3Ease of manufacture

If single-material rotor bars are used, then manufacturing simplicity is maintained, but performance optimization deteriorates

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidefficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The rotor bar is segmented into two distinct material zones along its length - an outer segment with aluminium and an inner segment with copper. This segmentation allows each zone to be optimized for its specific function while being manufactured as an integrated component through processes like differential solidification or selective material deposition.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The rotor bar employs a composite structure combining two different conductive materials - aluminium in the outer region and copper in the inner region. This composite material approach leverages the advantageous properties of each material: aluminium's high resistivity for starting torque enhancement and copper's low resistivity for efficiency improvement during normal operation.

Inventive Principle:

Principle #40Composite materials

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 results in improved starting torque and efficiency at steady-state operation, allowing the motor to maintain high torque per current performance and reduce resistive losses, particularly evident in the CuZn37 alloy configuration which offers superior starting characteristics and efficiency compared to single-material rotor designs.

Implementation Method 1

The part of the conducting element at the largest distance from the rotor axis will determine the starting characteristics at high slips as the current distribution is determined by the skin effect

Methodology Applied

Scientific EffectSkin effect: Skin Effect

Implementation Method 2

When the rotor is subject to a magnetic field from, e.g., a stator, a current is induced in the conducting elements and a torque is produced on the rotor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentEP3713050B1Induction motor

Publication Date: 2022.05.25 ABB (SCHWEIZ) AG

Figure 1~2
Figure 3a~4
Figure 5

AI summary

A rotor (3) for an electric machine (1) is described. The rotor (3) comprises a rotor axis (4) about which the rotor (3) is configured to rotate, and at least one conducting element configured to conduct current in the direction of the rotor axis (4). The rotor is characterized in that the resistivity within the conducting element decreases with a decreasing distance from the rotor axis (4).