This results in a more complicated rotor construction and expensive material selection, and sets higher standards for the manufacturing precision. The rotor of an induction motor can be a squirrel cage rotor or wound type rotor. Almost 70% of the industrial motors and drives comes under these category. Basically, it is the construction of rotor which makes squirrel cage induction motor different from wound type induction motor. Squirrel cage motors are the most commonly used induction motors, but the main drawback in them is their poor starting torque due to low rotor resistance. Shaded pole induction motors working and construction. A squirrelcage rotor is the rotating part of the common squirrelcage induction motor. This results in a more complicated rotor construction and expensive. Pdf squirrel cage rotor design and manufacturing for. Industrial application and case histories, first edition. Particularly, the squirrel cage type is simplicity, robustness and low cost, which has always made it very goodlooking and therefore, captured the leading place in industrial sector.
Control of motor characteristics by squirrelcage rotor design. Parida department of electrical engineering national institute of technology, silchar,assam, india email. A squirrelcage motor with this type of rotor construction is called. Design of a three phase squirrel cage induction motor for. The figure itself depicts many difference between the two types of motors. The entire structure looks like cage hence it is called a squirrel cage rotor. Also appreciate the rugged construction of squirrel cage rotor and know the spectacular reasons for the skewed arrangements of the rotor conductors. Several text books show how to compute rotor bar and end ring currents. A squirrelcage induction motor is one in which the secondary circuit consists of a squirrelcage winding suitably disposed in slots in the secondary core. Select number of stator slots and suitable three phase winding layout.
Advantages and disadvantages of squirrel cage induction motor. It is usually designed for fixedspeed operation, larger ratings having such features as deep rotor bars to limit direct on line dol starting currents. Kanpur, india design of a three phase squirrel cage induction motor for electric propulsion system ravi prakash,mohammad junaidakhtar, r. This simple and rugged construction makes it the favorite for most applications. At starting the 3 phase windings are connected to a star connected rheostat and during the running condition, the windings are shortcircuited at the slip rings. Because of the large rotor resistance, this motor has a pullout torque occurring at a high slip, and its starting torque is quite high. The rotating magnetizing field represented by the space vector b m or, equivalently by the magnetizing current i m moves at the synchronous speed. Horizontal squirrel cage mediumvoltage induction motor. So s1f1s2f2, and at starting the slip is equal to 1, so a unique value of. But increasing the rotor resistance for improving starting torque is not advisory as it will reduce the efficiency of the motor due to more copper loss.
Its torquespeed characteristic is also shown in figure 726. How are squirrel cage induction motors constructed. It consists of a cylinder of steel laminations, with aluminum or copper conductors embedded in its surface. Examine the construction of the squirrel cage induction motor module ems 8221, paying particulat attention to the motor, connection terminals and the wiring 2. It provides knowledge for industrial engineers, who use motor current signature analysis mcsa to determine if there are any cage winding breaks in their squirrel cage.
There are mainly two types of induction motor on the basis of power supply, single phase induction motor and three phase induction motor. Squirrel cage induction rotor winding failure mechanisms. The following are common methods to start a squirrel cage motor, depending upon the limitation, if. Current signature analysis for condition monitoring of cage induction motors. When a 3 phase supply is given to the stator winding it sets up a rotating magnetic field in space. Standard handbook of petroleum and natural gas engineering third edition, 2016. These motors are very robust in construction and very cheap. This simplest form of ac induction motor or asynchronous motor is the basic, universal workhorse of industry. Third international conference on advances in control and optimization of dynamical systems march 15, 2014. Those induction motors which employ squirrel cage rotor are called squirrel cage induction motors. The sinusoidally distributed flux density wave is moving at slip speed inducing in the rotor cage voltages of magnitude indicated by the blue vertical lines. How are high starting torques obtained in a squirrel cage. But the rotor construction differs with respect to the type which is specified above. An induction motor also known as an asynchronous motor is a commonly used ac electric motor.
In the slip ring type,the rotor consists of three phase winding similar to that of the stator winding. Consequently, a small starting torque is developed. Squirrel cage and wound rotor or slip rig induction motor. Control of motorcharacteristics by squirrelcage rotordesign. Several text books show how to compute rotor bar and end ring currents, resistances. Three phase induction motor construction electrical academia. The motor accelerates to a speed slightly below the synchronous speed and runs as a. Pdf squirrel cage rotor design and manufacturing for high. Design, construction, and manufacture of squirrel cage rotors. In squirrel cage induction motors, rotor windings wound in squirrel cage. And in the previous article on types of electrical motors, we have classified induction motors based on the type of rotor used. What is the difference between a slip ring and a squirrel.
The construction of stator of the induction motor is almost the same as other motors. Pdf improving squirrel cage induction motor efficiency. Please have a look at the below figures of squirrel cage induction and wound rotor slip ring induction motor. According to the labelled notation a represents stator b rotor c bearing shields d fan e ventilation grill and f terminal box. Rotor material selection and construction topology influence on the electrical machine design are discussed. Closedform analysis of squirrelcage induction motors with. In operation, the nonrotating stator winding is connected to an alternating current power source. A squirrelcage rotor is the rotating part of the common squirrel cage induction motor. However, should the motor require service, this manual includes a section that assists the. Select specific electric loading ac ampere conductors per meter of air gap circumference from. Almost 95% of the induction motors used is of squirrel cage type. Three phase squire cage induction motor, fully enclosed. Their susceptibility to failure is dependent on the type of winding construction, the motor application, operating duty, winding geometry, and the materials of construction.
The rotor is constructed using a number of single bars shortcircuited by end rings and arranged in a hamsterwheel or squirrelcage configuration. As there are no brushes and slip ring, these motors requires less maintenance. Most of single phase induction motors use squirrel cage rotor as it has a remarkably simple and robust construction enabling it to operate in the most adverse circumstances. This rotor consists of uninsulated copper or aluminium bars, placed in the slots. Squirrel cage rotor type, which comprises a set of copper or aluminum bars installed into the slots, which are connected to an endring at each end of the rotor. Traditional design of cage rotor induction motors publish. Starting torque is directly proportional to the rotor resistance. Improving squirrel cage induction motor efficiency. The squirrel cage induction motor is by far the most common type of induction motor. Know about the different winding slots, lamination of the stator and its construction. The rotor is of the squirrel cage type and is under the influence of this moving field.
These motors are having the difference in rotor construction. The motor which employing squirrel cage type rotor is known as the squirrel cage motor. Electrical interview questions which motor is best. The laminations are aligned and heatshrunk onto the shaft, and then the molten aluminum is forced into the slots to form the squirrel cage. Design, construction, and manufacture of squirrel cage. Designing of three phase squirrel cage induction motor for. The squirrel cage rotor consists of laminated steel in the core with evenly spaced bars of copper or aluminum placed axially around the periphery, permanently shorted at the ends by the end rings. This chapter presents the essential features of the design, construction, and manufacture of squirrel cage induction rotors. But the rotor construction differs with respect to the type of motor. Cylindrical laminated core rotor is wound like winding on the stator. Squirrelcage rotor design and manufacturing for high. Induction motor construction squirrel cage rotor duration.
This rotating magnetic field has a speed which is known as the synchronous speed this rotating magnetic field induces the voltage in rotor bars and hence shortcircuit currents start flowing in the rotor bars. Difference between squirrel cage and slip ring induction motor. Based on the rotor construction, 3 phase induction motor can be of two types. A highspeed squirrel cage induction machine requires a totally different design compared to the traditional squirrel cage industrial motor because of the mechanical limitations caused by the high speed. The induction motor are of two types based on the construction of rotor. In this article, we will learn about squirrel cage and slip ring induction motors. In an induction motor, the electric current in the rotor needed to produce torque is obtained via electromagnetic induction from the rotating magnetic field of the stator winding. The bars are permanently shorted at both the ends with the help of conducting rings called end rings. As soon as this torque starts to revolve the rotor, additional torque is produced by singlephase inductionmotor action. Cage rotors are cast or fabricated of aluminum, copper, or other metals. Basic construction of 3phase ac induction motors you. In the induction motors used in lift and hoists, you will see a type of rotor called a slip ring rotor, whereas in most of the other applications you will see a simpler, squirrel cage type of rotor. The construction of stator for any induction motor is almost the same. Veinott, theory and design of small induction motors, new york.
Squirrel cage induction motor is used in lathes, drilling machine, fan, blower printing machines etc. Most of 3phase induction motors use squirrel cage rotor as it has a remarkably simple and robust construction enabling it to operate in the most adverse circumstances. Analysis and design of ac induction motors with squirrel cage rotors. A highspeed squirrelcage induction machine requires a totally. However, it suffers from the disadvantage of a low starting torque. Using variable voltage variable frequency vvvf drive. It provides knowledge for industrial engineers, who use motor current signature analysis mcsa to determine if there are any cage winding breaks in their squirrel cage induction motors scims. Rotor the rotor need not receive external power or excitation other than from the stator. Squirrelcage rotor design and manufacturing for highspeed. The rotor of the motor consists the cylindrical laminated core having semiclosed circular slots and short circuit at each end by copper or aluminium ring, called short circuiting ring. A identify the stator windings note that they consist of many tuns of small diameter wize evenly spaced axound the stator.
The rotor consists of a cylindrical lamina ted core with parallel slots for carrying the rotor conductors which, it should be. Pdf design and fabrication of high efficiency squirrel cage. In the project has been done an analysis of the mathematical equations of the whole system. Squirrelcage rotor almost 90 per cent of induction motors are squirrelcage type, because this type of rotor has the simplest and most rugged construction imaginable and is almost indestructible. The squirrel cage induction motor was designed for an extended service life under very demanding conditions.
Squirrel cage wound rotor with slip rings the rotating magnetic field the basic idea of an electric motor is to generate two magnetic fields. The construction of these rotor windings resembles a squirrel cage. Know about the most popular and almost unbreakable construction of squirrel cage induction motor. The starting of an induction motor does not relate to simple switching alone. A squirrel cage motor with this type of rotor construction is called nemadesign class d. Keeping the vf ratio constant, when frequency is reduced then that results in constant slipfrequency at running. There are other types of rotors used in ac motors such as synchronous and wound rotor, however, the focus here will be on the squirrel cage. The construction of the rotor is rugged and simple.
The squirrel cage induction motors are 90% used in various industrial, domestic and commercial applications. The rotor cage is similar in appearance to pet rodent exercise wheels from over a century ago, thus the name squirrel cage. When voltage is applied to the stator winding, a rotating magnetic field is established. Aluminum rotor bars are usually diecast into the rotor slots, which results in a very rugged construction. Squirrel cage induction motor the engineering projects. It also involves its switchgears to control its starting inrush current, starting torque, or both, and its overload and shortcircuit protection. Compared to the squirrel cage rotor, the rotor construction is not simple. The starting torque of the squirrelcage rotor can be increased by shaping the rotor bars. The rotor is built of a stack of steel laminations, such as the one shown in figure 3. Squirrel cage rotor design and manufacturing for highspeed applications article pdf available in ieee transactions on industrial electronics pp99. In simple words, the type of 3 phase induction motor which uses a squirrel cage rotor is called squirrel cage induction motor. Dont worry, difference between squirrel cage and slip ring type induction motor is tabulated after the figure.
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