Squirrel Cage Induction Motor

In the case of a squirrel cage induction motor, the geometry is regular and periodic.

From: Finite Elements, Electromagnetics and Design, 1995

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Modelling of ac rotating machines

Nasser D. Tleis BSc, MSc, PhD, CEng, FIEE, in Power Systems Modelling and Fault Analysis, 2008

‘Fixed’ speed induction generators

These are essentially similar to squirrel-cage induction motors and are driven by a wind turbine prime mover at a speed just above synchronous speed, normally upto 1% rated slip for today's large wind turbines. Because the speed variation from no load to full load is very small, the term ‘fixed’ speed tends to be widely used. The generator is coupled to the wind turbine rotor via a gearbox as shown in Figure 5.29. The design and construction of the stator and rotor of an induction generator are similar to that of a large induction motor having a squirrel-cage rotor.

Figure 5.29. Fixed speed wind turbine induction generator

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Electrical Distribution and Installation

I G Crow, R Robinson, in Plant Engineer's Handbook, 2001

Squirrel-cage induction motor

The principal advantages of the squirrel-cage induction motor are its simplicity of design and robust construction. Its torque/speed and current/speed characteristics are such that, on starting, a torque of typically twice full-load torque is produced but a large current (typically, six to eight times full-load current) is drawn from the supply. It is this latter aspect of the current drawn upon starting which is important in deciding upon the type of starting equipment needed for a squirrel-cage motor because


The drawing of a large current from the supply will cause a corresponding voltage drop at the point of common coupling with other consumers. This will affect other drives within the installation or consumers fed from the same supply authority.


If the motor drives plant of high inertia (e.g. fans) the time during which the large current is drawn may be extended. Such a current flowing for an extended period may cause the unwanted operation of overload or over-current protection relays within the supply system.

In order to overcome (1) it is often necessary to introduce a form of assisted starting, which can also help in overcoming problem (2). However, modification of the overload protection device characteristics may also be necessary.

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S.J. Salon, ... G. Reyne, in Finite Elements, Electromagnetics and Design, 1995

4.2.1 Mesh Generation

In the case of a squirrel cage induction motor, the geometry is regular and periodic. This was taken advantage of in the mesh generation strategy. The mesh was formed using a mapping function which subdivided each region of the motor. The regions are defined in Figure 4.2.1.

Figure 4.2.1. Topological Regions of an Induction Motor

The innermost region is the rotor core. This region represents the space between two cylinders, one at the motor shaft and the other at the bottom of the rotor slots. The inner circle is divided into a number of equal parts set by the user. Each rotor slot and the root of the tooth is likewise divided into a user defined number of segments. Then the number of intervening layers and weights is specified. The resulting mesh is generated layer by layer from the inner circle to the outer circle. The method uses a weighting function (Hwang, Salon and Palma 1988) which refers to Figure 4.2.2.

Figure 4.2.2. Division of Motor into Layers


where AB and GH refer to the arc lengths, NB and NA are the specified number of segments along these arcs, and R is as shown in Figure 4.2.2. The total number of layers is then

(4.2.2)N=NINT[log(AB/NBGH/NA)log W]

where NINT returns the nearest integer to the argument. The length, d1, is found as


The number of segments on this layer is


To find the next layer, we recompute W, replace N by N-1 and R by R −d1 and so on. The first step in predicting the magnetic vibration characteristics of a particular electric machine is to analyze the dynamic magnetic field acting in the machine. The magnetic field data may then be used to compute forces and force distributions, which are then in turn applied to a mechanical model of the machine and used to predict vibrations.

Consider the case illustrated in Figure 4.2.2, with NA segments on the inner circle and NB segments on the outer segment. The interior nodes will all be placed on circles whose radii are completely determined by the number of layers and weights. It only remains to determine the number of nodes (or segments) on each circle.

The rotor tooth and slot section exhibits symmetry over each half slot pitch. The geometry is specified in Figure 4.2.3.

Figure 4.2.3. Slot and Tooth

The number of layers and weighting is specified as in the case of the rotor core and the mesh is generated for the half slot using Equation (4.2.4). The mesh is then reflected around the center line of the slot and repeated Nr times, where Nr is the number of rotor slots. The mesh regions are different from the material regions. The material properties are specified independently. With this extra flexibility, the rotor meshing region contains one layer of elements in the air gap as shown above. The reason for this choice will be explained below in the discussion of the moving mesh.

The air gap region is an annular region similar to the rotor core and is meshed in the same way. Note that the air gap mesh region docs not correspond exactly to the air gap since one layer of the actual air gap is meshed with the rotor and one with the stator.

The stator tooth and slot region (and one layer of elements in the air gap) is treated like the rotor tooth and slot region above. The stator core region is treated like the rotor core region.

As the rotor turns, the air gap elements must be continualy remeshed. In the analysis which follows, we show that for electromagnetic purposes, the rotor is modelled in its own reference frame. The rotor core and slot-tooth regions are not remeshed, only rotated. The stator core and slot-tooth regions remain stationary. It is only the air gap region (excluding the part of the air gap attached to the rotor mesh and stator mesh as described above) which is continuously changing. The mesh is generated in such a way that the air gap region lies between two circles with uniform node spacing. The remeshing is accomplished (when needed) without adding any new nodes or elements. The algorithm only reconnects existing elements using the new nodal positions. This is illustrated in Figure 4.2.4 for two instants of time.

Figure 4.2.4. Remeshing of the Air Gap Layers

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M.V.K. Chari, S.J. Salon, in Numerical Methods in Electromagnetism, 2000

Squirrel Cage Induction Motor

We consider a three-phase squirrel cage induction motor. The motor is rated at 5 hp. The parameters of the motor are listed in Table 10.1. In this example the entire motor winding is represented. The inputs are the instantaneous voltages at the three terminals. The currents in the windings are unknown. The rotor is free to turn. Each rotor bar is represented as an independent circuit connected to an end ring that has a constant resistance and inductance. The mesh in the air gap may or may not be remeshed at each time step, depending on the distortion of the elements. In any case, the remeshing is done so that the number of nodes and elements remains the same. The sequence of plots in Figures 10.4, 10.5, and 10.6 shows the motor operating at full load at various positions in a cycle.

Table 10.1. Electrical and Mechanical Parameters of 5-HP Induction Motor

Parameter Value Units
Voltage source Phase voltage 220 V
Frequency 50 Hz
Resistance/phase 0.13 Ω
Inductance/phase 0.02 mH
Winding coils DC resistance 0.951 Ω
Lead inductance 4.87 mH
Winding type Double layer
Pole pitch 6 slots
Number of turns 160 turns
Rotor end ring Interbar resistance 2.10 μΩ
Interbar inductance 0.04 μH
Rotor load Inertia 6.191 · 10−3 kg·m2
Rotor bars Electric conductivity 4.90 · 107

Figure 10.4. Equipotential Plot at One Instant

Figure 10.5. Plot at a Later Time

Figure 10.6. Plot at a Still Later Time

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Improving Machinery Reliability

In Practical Machinery Management for Process Plants, 1998

Motor Life Insurance Terms

To maximize the life and performance of AC squirrel-cage induction motors in process industry applications, one must have:

A motor with the proper design (A, B, C, D, or E) for the application

An enclosure properly configured to protect the motor from environmental contamination

An adequately sized motor to handle the load requirements

A conservatively designed (or applied) motor that will allow it to work well within its designed thermal capacity

A proper installation that assures good alignment, eliminates vibration, and does not transfer unwanted external loads to the motor

An adequately designed and maintained (if required) bearing lubrication system

A motor environment that provides adequate air circulation and maintains the effectiveness of motor heat removal or ventilation systems

A regulated power supply that supplies the correct voltage, maintains voltage balance between phases and provides protection against over currents

A load cycle designed to avoid frequent starts and other causes of motor overheating.

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Electric Motors

Anibal de Almeida, Steve Greenberg, in Encyclopedia of Energy, 2004

1.1.1 Squirrel-Cage Induction Motors

The vast majority of the motors used in industry are squirrel-cage induction motors (Figs. 1 and 2) due to their low cost, high reliability, and fairly high efficiency. These motors also use more of the total electrical energy than any other motor type in homes and buildings. The three-phase induction motor, invented in the 1890s, is composed of three sets of stator (the stationary part of the motor) windings arranged around the stator core (a stack of steel laminations with slots for the windings).

Figure 1. Diagram of squirrel-cage induction motor.

Figure 2. Squirrel-cage induction motor. (A) General structure. (B) Rotor squirrel cage (bars and end rings).

There are no electrical connections to the rotor (the rotating part of the motor), which means that there are fewer wearing parts to maintain and replace. When the three stator windings are fed by a three-phase alternating current (AC) supply, a rotating magnetic field is generated, the rotating speed of which is determined by the frequency of the power supply and by the number of magnetic poles of the motor. If the motor is fed by 60 Hz and has two pairs of poles as in Fig. 1, the speed of the rotating field will be 1800 revolutions per minute (rpm). When the rotating field crosses the squirrel-cage rotor (so named because the cylindrical shape of the conducting rotor bars resembles a squirrel cage), the variable magnetic flux induces currents in the rotor bars (hence the name induction motor), which leads to a pulling torque in the direction of the rotating field. The rotor accelerates to a speed close to the speed of the rotating field speed (synchronous speed), but never is able to reach it. If the two speeds were equal, there would not be a change in the magnetic flux (of the stator relative to the rotor), and thus no induced currents, and therefore no torque. The induction motor speed decreases by a few percent when the motor goes from no load to full-load operation. The full-load speed is a function of the motor design and power and is usually in the range of 94–99% of the synchronous speed; the difference is the “slip.” Figure 2 shows the typical construction of a squirrel-cage induction motor. The rotor squirrel cage, detached from the steel laminations can also be seen.

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Mechanical plant electrical services

In Electrical Systems and Equipment (Third Edition), 1992

8.2.9 Conveyors

Conveyors are driven by 415 V three-phase 50 Hz squirrel-cage induction motors through fluid couplings to protect conveyors during start-up. The motors are totally-enclosed, fan cooled with protection to IP55.

Each conveyor is equipped with an emergency trip-wire system running the full length of the conveyor alongside the access way. Switches are located at intervals along the trip wire. The trip wire may be a wire rope, arranged to operate trip switches directly, or a low voltage electric cable arranged to operate a trip relay. In the latter system, a trip relay is energised through the cables and the switches between which they are suspended. Upon deflection of a cable, the relay circuit is broken by the associated switches. Since a cable fault or breakage will also cause the trip relay to operate, the system is self-monitoring.

The contacts of the trip switches or relays are connected directly into conveyor drive-motor contactor circuits and cause the conveyors to stop when the trip is operated.

Each conveyor is fitted with a speed detector. Belt-driven speed detectors are prone to slip when dusty or wet and have been dropped in favour of electronic pulse or similar types. The conveyor is tripped if the conveyor belt slips or breaks.

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Modelling of voltage-source inverters, wind turbine and solar photovoltaic (PV) generators

Nasser Tleis BSc (Hons), MSc, PhD, CEng, FIET, M-CIGRE, in Power Systems Modelling and Fault Analysis (Second Edition), 2019

6.4.1 Modelling and analysis of short-circuit current contribution

Type 1 fixed-speed induction generators are essentially similar to squirrel-cage induction motors. These are driven by a wind turbine prime mover at a speed just above synchronous speed, normally up to 1% rated slip for today’s large wind turbines. Because the speed variation from no load to full load is very small, the term ‘fixed’ speed is widely used. The generator is coupled to the wind turbine rotor via a gearbox as shown in Fig. 6.4. The design and construction of the stator and rotor of an induction generator are similar to those of a large induction motor with a squirrel-cage rotor.

Figure 6.4. Type 1 fixed-speed wind turbine induction generator.

In Chapter 5, Modelling of rotating ac synchronous and induction machines, we presented the modelling of induction motors and analysed their short-circuit current contribution. The positive- and negative-sequence short-circuit contribution of a fixed-speed induction generator can be represented in a similar way to that of an induction motor. The equations of transient reactances and time constants derived for induction motors can also be used for induction generators. The stator windings of these generators are usually connected in delta or star with an isolated neutral. Thus their zero-sequence impedance to the flow of zero-sequence currents is infinite.

Using Eq. (5.112b), to represent a single-cage fixed-speed induction generator, the instantaneous short-circuit currents delivered by the machine for a three-phase solid fault at its terminals are given by




and θo is the instant of fault occurrence on machine stator phase r voltage waveform and the machine parameters are as given in Chapter 5, Modelling of rotating ac synchronous and induction machines.

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Data charts and tables

Peter D. Osborn BScEng (Hons), C Eng, FIEE Engineering Consultant, in Handbook of Energy Data and Calculations, 1985

A38 Induction motors

38.1. Typical performance values for standard three-phase 415 V 50 Hz T.E.F.C. squirrel cage induction motorsa

Output((kw)) Speed rev/min Efficienc Power factor Motor input (full load)
Full load 0.75 load 0.5 load Full load 0.75 load 0.5 load Amp kW kVA
0.75 1425 71 68 62 0.71 0.63 0.51 2.06 1.06 1.49
910 68 67 62 0.66 0.60 0.50 2.32 1.10 1.67
715 65 63 54 0.54 0.47 0.37 2.97 1.15 2.14
1.10 1410 75 74 69 0.75 0.67 0.53 2.72 1.47 1.96
910 76 76 73 0.69 0.61 0.48 2.92 1.45 2.10
705 69 66 60 0.59 0.50 0.39 3.76 1.59 2.70
1.50 2880 77 75 71 0.88 0.78 0.72 3.08 1.95 2.21
1400 76 76 73 0.79 0.72 0.61 3.48 1.97 2.50
950 75 73 70 0.68 0.58 0.46 4.09 2.00 2.94
720 75 74 69 0.56 0.46 0.36 4.97 2.00 3.57
2.20 2875 79 78 75 0.89 0.84 0.77 4.35 2.78 3.13
1435 79 76 72 0.78 0.69 0.56 4.97 2.78 3.57
955 80 79 77 0.73 0.65 0.51 5.24 2.75 3.77
720 79 77 73 0.62 0.54 0.42 6.25 2.78 4.49
3.00 2840 80 79 76 0.86 0.81 0.69 5.64 3.49 4.06
1440 81 80 77 0.77 0.69 0.56 6.69 3.70 4.81
960 82 81 77 0.72 0.66 0.54 7.07 3.66 5.08
725 78 77 75 0.71 0.63 0.51 7.54 3.85 5.42
5.50 2900 83 83 80 0.86 0.83 0.75 11.1 6.63 7.98
1440 85 85 83 0.75 0.67 0.55 12.0 6.47 8.63
975 86 85 83 0.77 0.72 0.59 11.6 6.40 8.31
730 84 83 81 0.79 0.75 0.61 11.5 6.55 8.29
7.50 2885 85 85 84 0.90 0.90 0.86 13.6 8.82 9.80
1440 86 86 85 0.82 0.80 0.71 14.8 8.72 10.64
975 84 83 79 0.76 0.71 0.57 16.3 8.93 11.75
725 84 84 82 0.79 0.73 0.62 15.7 8.93 11.30
15.0 2940 85 84 80 0.88 0.85 0.80 27.9 17.6 20.1
1460 87 87 85 0.86 0.82 0.76 27.9 17.2 20.0
975 88 88 87 0.82 0.78 0.70 28.9 17.0 20.8
30.0 2955 87 85 82 0.91 0.89 0.84 52.7 34.5 37.9
1475 90 90 88 0.86 0.84 0.78 53.9 33.3 38.8
980 90 90 89 0.82 0.79 0.71 56.5 33.3 40.6
55.0 2960 91 90 86 0.90 0.90 0.88 93.4 60.4 67.2
1475 91 91 90 0.88 0.86 0.84 97.8 60.4 70.3
985 91 91 89 0.84 0.80 0.71 105 60.4 75.5
75.0 2960 91 90 86 0.92 0.91 0.88 125 82.4 89.5
1475 92 91 89 0.88 0.86 0.81 129 81.5 92.6
985 92 91 90 0.85 0.83 0.76 133 81.5 95.9
90.0 2970 91 90 86 0.91 0.90 0.84 151 98.9 109
1480 92 91 90 0.87 0.85 0.80 156 97.8 112
985 92 91 90 0.85 0.84 0.80 160 97.8 115
110.0 2970 92 91 88 0.91 0.90 0.87 183 120 131
1480 92 91 89 0.87 0.83 0.77 191 120 137
985 92 91 90 0.86 0.83 0.77 193 120 139
132.0 2955 92 92 89 0.93 0.93 0.91 215 143 154
1480 92 91 89 0.86 0.83 0.77 232 143 167
985 92 91 89 0.83 0.81 0.74 240 143 173
These values should be used as a guide as they vary with manufacturer and can be improved, but usually at a price premium.
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Prime movers for fans

WTW (Bill) Cory, in Fans and Ventilation, 2005

Types of electric motor


Alternating current (AC) motors


3-phase motors

Squirrel cage induction motors

Wound-rotor induction motors

Synchronous motors

Polyphase AC commutator motors


Single-phase AC motors

AC series motor

Single phase AC capacitor-start, capacitor-run motors

Single phase AC capacitor-start, induction-run motors

Single-phase AC split phase motors

Single-phase shaded pole motors


Single-phase repulsion-start induction motor


Direct current (DC) motors

Series wound motors

Shunt wound motors

DC compound wound motors


“Inside-out” motors

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