# Thermal Analysis and Cooling Strategies of High-Efficiency Three-Phase Squirrel-Cage Induction Motors—A Review

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## Abstract

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## 1. Introduction—Induction Motors

#### 1.1. Losses in a Squirrel-Cage Induction Motor

^{2}R losses, iron core losses, eddy-current losses, hysteresis losses, surface losses, losses because of flux pulsation, and mechanical losses [12,13,14]. Mechanical losses cannot be estimated analytically, so these losses will not be considered in the following simulations.

^{2}R losses in the stator and rotor windings can be represented with Equation (1).

_{1}and R

_{2}represent the winding resistance, m represents the number of phases, and I is the supply current.

_{1,0}represents the specific losses of the iron used, f represents the frequency of the supply, k

_{dj}represents the coefficient of heterogeneous distribution of the FD, B

_{j}is the average FD, and m

_{j}represents the magnetic circuit weight of division. The surface losses of the iron core in the air gap are described by:

_{1}represents the inner diameter of the stator, α is the coverage coefficient of poles, l

_{e}is the stator/rotor packet length, K

_{0}is the surface loss factor, Q

_{1,2}is the number of slots, n is the RPM, t

_{d}

_{1}is the slot pitch, and β

_{δ}is the pulsation in air gap FD. β

_{0x}depends on the ratio of slots opening and the air gap length in the stator teeth. The pulsating-magnetic-flux-caused set teeth losses are described by:

_{j}

_{1,2}is the stator/rotor teeth weight, B

_{p}

_{1,2}is the FD magnitude of the saturating stator/rotor teeth, and Q

_{1,2}is the number of slots.

#### 1.2. Hotspots in a Squirrel-Cage Induction Motor

## 2. Thermal Analysis of High-Efficiency Three-Phase Cage Induction Motors

#### 2.1. LPTN—Lumped-Parameter Thermal Network Modeling Method, a Computational Approach

- (i)
- Conduction

- (ii)
- Convection

- (iii)
- Radiation

#### 2.2. Thermal Investigation through Finite Element Method (FEM), a Computational Approach

_{s}is the solid body temperature, T

_{f}is the fluid temperatures, and Nu is the Nusselt number, which is represented as:

#### 2.3. Experimental Analysis to Compare the Motor Efficiency of Copper and Aluminum Rotors

^{2}R losses) and core losses. As the torque and speed increase, the mechanical power output increases, and the copper losses also increase due to the higher current, reducing the motor’s efficiency. However, the effect of the torque and speed on the efficiency depends on the load conditions and the design of the motor. Different motors may have different efficiency profiles.

- − Copper rotors typically have a lower resistance than aluminum rotors, which can lead to lower copper losses and a potentially higher efficiency under heavy loads.
- − Aluminum rotors are lighter, which can reduce the moment of inertia and improve the acceleration performance. This can be advantageous in certain applications.

#### 2.4. Experimental Analysis of the Stator of an Induction Motor

#### 2.5. Materials for Parts of Squirrel-Cage Motor

## 3. Cooling Strategies of High-Efficiency Three-Phase Cage Induction Motors

#### 3.1. Water-Cooling System

_{p}is tie specific heat capacity, T is the temperature, λ is the heat conductivity, and P is the heat generation rate.

_{f}is the frame temperature, T

_{w}is the water temperature, h is the frame, and HTC is the fluid convective heat transfer coefficient.

#### 3.2. Oil-Cooling Systems

#### 3.3. Natural Water-Cooling Capillaries (NWCC) Method

#### 3.4. Energy Harvesting and Self-Powered Induction Motor with Thermal Analysis

#### 3.5. Miscellaneous Methods of Thermal Management

## 4. Future Scope

## 5. Summary

## Funding

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

CFD | Computational fluid dynamics |

SW | Side windings |

FD | Flux density |

EW | End windings |

SCIM | Squirrel-cage induction motor |

IM | Induction motor |

LPTN | Lumped-parameter thermal network |

LPCM | Lumped-parameter circuit method |

FEA | Finite element analysis |

HTC | Heat transfer coefficient |

RTD | Resistance temperature detectors |

TEFC | Totally enclosed fan-cooled |

NWCC | Natural water-cooling capillaries |

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**Figure 2.**Overheating of a squirrel-cage induction motor [16].

**Figure 4.**Schematic depicting the direction of heat flow [26].

**Figure 5.**Graphic representation of the thermal network [26].

**Figure 6.**Efficiency of an aluminum rotor [31].

**Figure 7.**Efficiency of a copper rotor [31].

**Figure 8.**Squirrel-cage rotor: (

**a**) conductor bars and end rings before assembly; (

**b**) steel core, conductor bars, and rings after assembly; (

**c**) sectional view of the squirrel-cage rotor [34].

**Figure 9.**Axial water flowing through the induction motor housing [45].

**Figure 10.**Tangential water flowing through the induction motor housing [45].

**Figure 11.**Conceptual configuration of an induction motor with high-temperature superconducting (HTS) squirrel cage [48].

**Figure 12.**Toroidal and hairpin winding [52].

**Figure 13.**Oil-cooling circuit of the motor housing [54].

**Figure 14.**Structure of capillary jacket and capillary tube [55].

t (s) | Temperature, °C (Rotor Tooth) | Temperature, °C (Rotor Surface) | Temperature, °C (Stator Tooth) | Temperature, °C (Stator Surface) | Temperature, °C (End Cap) | Temperature, °C (Shaft Surface) |
---|---|---|---|---|---|---|

0 | 40 | 40 | 40 | 40 | 40 | 40 |

4.5 | 40.4 | 40.3 | 40.1 | 40.2 | 40.3 | 40.1 |

9 | 41.3 | 40.4 | 40.2 | 40.5 | 40.4 | 40.1 |

13.5 | 41.9 | 40.6 | 40.3 | 40.6 | 40.6 | 40.2 |

18 | 42.3 | 40.8 | 40.4 | 40.8 | 40.8 | 40.3 |

22.5 | 42.5 | 41 | 40.5 | 41.1 | 41 | 40.3 |

27 | 42.9 | 41.2 | 40.8 | 41.3 | 41.2 | 40.4 |

31.5 | 43.3 | 41.5 | 40.8 | 41.6 | 41.5 | 40.5 |

36 | 43.5 | 41.6 | 40.9 | 41.8 | 41.6 | 40.6 |

40.5 | 43.8 | 41.8 | 40.9 | 42.1 | 41.9 | 40.8 |

t (min) | Temperature, °C (WindEW) | Temperature, °C (WaterEW) | Temperature, °C (WindSW) | Temperature, °C (WaterSW) | Temperature, °C (WindYoke) | Temperature, °C (WaterYoke) |
---|---|---|---|---|---|---|

0 | 20 | 20 | 20 | 20 | 20 | 20 |

10 | 90 | 61 | 91.5 | 59 | 50 | 30 |

20 | 105 | 69 | 107 | 66 | 66 | 31 |

30 | 119 | 72 | 120 | 69 | 72 | 31 |

40 | 122 | 73 | 124 | 70 | 80 | 33 |

50 | 129 | 75 | 130 | 72 | 84 | 33 |

60 | 132 | 77 | 133 | 75 | 89 | 34 |

70 | 134 | 77 | 136 | 75 | 91 | 34 |

80 | 137 | 78 | 139 | 77 | 91 | 34 |

90 | 139 | 79 | 139 | 78 | 92 | 34 |

Component | Temperature (°C) | ||
---|---|---|---|

Air-Cooled | Water-Cooled | % Decrease in Temp. | |

End windings | 119 | 72 | 39.49% |

Slot windings | 120 | 70 | 41.67% |

Yoke | 72 | 31 | 56.95% |

Component | Material | Power Density | Efficiency Increment | Cooling Scheme | Reference |
---|---|---|---|---|---|

Rotor | Epoxy composite containing magnetic powder | Yes | Yes | Air cooling | [34] |

Aluminum | Yes | Yes | Air cooling | [35] | |

Soft magnetic materials | Yes | Yes | Air cooling | [33] | |

Copper, silicon copper | Yes | Yes | Air cooling | [36,37] | |

Spindle shaft | Fiber-reinforced composite materials | Yes | Yes | Air cooling | [34] |

Conductor frame | Iron powders and ferrite powders | Yes | Yes | Air cooling | [34] |

Casing | Aluminum | Yes | Yes | Air cooling | [35] |

End ring | Aluminum | Yes | Yes | Air cooling | [35] |

Stator core | Arnon7, nickel steel carpenter, and M19_24G | Yes | Yes | Air cooling | [38] |

Stator liner | Nomex 430430 | Yes | Yes | Air cooling | [35] |

Stator slot | Silicon steel | Yes | Yes | Air cooling | [20,35] |

Cooling Scheme | The Component That Is Cooled | Pattern of Cooling | Reference |
---|---|---|---|

Water cooling | Motor housing | Axial water flow and tangential water flow | [45] |

Stator | Axial water flow and tangential water flow | [45] | |

Immersed cooling | Motor housing | SCIM is submerged in the liquid | [47,48] |

Oil or splash-based cooling | Copper coils | Direct spraying of oil on the copper coils | [22,24,47] |

Totally enclosed fan-cooled (TEFC) scheme | Motor housing | Air flow around the housing | [46] |

Totally enclosed water-cooled scheme | Stator winding and the rotor | Radial and axial directions of water flow | [53] |

Natural water-cooling capillaries (NWCC) | Shielding of insulation material | Natural ventilation systems surrounding the motor | [54] |

Baffles in coolant pipes/air cooling | Stator | Coolant pipes with baffles | [61] |

Heat pipe/air cooling | Motor housing | Heat pipe mounted in the housing | [13] |

Nano-liquid/mixed liquid/air cooling | Motor housing | Axial water flow and tangential water flow | [13] |

Porous geometry/air cooling | End winding | Region of porous geometry | [9] |

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**MDPI and ACS Style**

Konda, Y.R.; Ponnaganti, V.K.; Reddy, P.V.S.; Singh, R.R.; Mercorelli, P.; Gundabattini, E.; Solomon, D.G.
Thermal Analysis and Cooling Strategies of High-Efficiency Three-Phase Squirrel-Cage Induction Motors—A Review. *Computation* **2024**, *12*, 6.
https://doi.org/10.3390/computation12010006

**AMA Style**

Konda YR, Ponnaganti VK, Reddy PVS, Singh RR, Mercorelli P, Gundabattini E, Solomon DG.
Thermal Analysis and Cooling Strategies of High-Efficiency Three-Phase Squirrel-Cage Induction Motors—A Review. *Computation*. 2024; 12(1):6.
https://doi.org/10.3390/computation12010006

**Chicago/Turabian Style**

Konda, Yashwanth Reddy, Vamsi Krishna Ponnaganti, Peram Venkata Sivarami Reddy, R. Raja Singh, Paolo Mercorelli, Edison Gundabattini, and Darius Gnanaraj Solomon.
2024. "Thermal Analysis and Cooling Strategies of High-Efficiency Three-Phase Squirrel-Cage Induction Motors—A Review" *Computation* 12, no. 1: 6.
https://doi.org/10.3390/computation12010006