Control of motorcharacteristics by squirrelcage rotordesign the reactance x2 in an induction motor equivalent circuit represents the referred form of the rotors leakage reactance. Speed torque characteristics of induction motor from eq. Construction of double squirrel cage induction motor a double squirrel cage induction motor consists of a rotor which has two independent cages one above the other in the same slot. It is usually designed for fixedspeed operation, larger ratings having such features as deep rotor bars to limit direct on line dol. The upper slot conductors from the outer cage and the lower slot conductors form the inner cage. The outer cage bars have a smaller crosssectional area than the inner bars and are.
Stator is made up of number of stampings in which different slots are. Doublecage induction motors behavior under flicker conditions. However, it suffers from the disadvantage of a low starting torque. Wound rotor induction motors ac motors electronics.
As the name indicates, the double cage induction motors have two cages in the rotor and they have the advantages of both squirrel cage induction motors and wound rotor induction motors. It also involves its switchgears to control its starting inrush current. Double cage induction motor electrical engineers guide. Double squirrel cage induction motor your electrical guide. An induction motor or asynchronous motor is an ac electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. In the squirrel cage induction motor the rotor slots are usually given slight skew a to reduce the magnetic hum and locking tendency of the rotor b to increase the tensile strength of the rotor bars c to ensure easy fabrication d none of the above ans. Wound rotor induction motor is used in applications which require smooth start and adjustable speed. Bars of outer cage have small cross sectional area than the inner cage bars and it is made up of highresistivity materials. The squirrelcage winding in this design consists of two layers of bars shortcircuited by end rings. However, the slip at which the maximum torque occurs changes with rotor resistance. Former is cheaper and broadly used as it requires less maintenance than later one. Here in this equation the starting torque of induction motor tsh is proportional to rotor resistance r2.
X depend on the shape and size of the rotor slot, the conductor material and the rotor current frequency. Starting torque is directly proportional to the rotor resistance. Therefore for motor startup simulations, the double cage model is. A double cage motor develops higher starting torque for low starting current and. Their sole purpose is to allow resistance to be placed in series with the rotor windings while starting figure below. Many papers have been published on the singlecage model parameter. In operation, the nonrotating stator winding is connected to an alternating current power source. It is called a squirrel cage motor because the rotor inside of it known as a squirrel cage rotor looks like a squirrel cage. Analytical modeling of double cage rotor induction motors in healthy and broken bars conditions conference paper pdf available november 2014 with 810 reads how we measure reads. An induction motor can therefore be made without electrical connections to the rotor. The basic idea of an electric motor is to generate two magnetic fields. Know about the different winding slots, lamination of the stator and its construction. The model of doublecage induction motor for the analysis of thermal fields in transient operations article pdf available january 2017 with 1,335 reads how we measure reads.
Dec 26, 2015 in this small post we will discuss about the double cage induction motor in brief. Typically k r is in the range of 1 to 5, and k x is in the range of 0. Recall that leakage reactance is the reactance due to the rotor flux lines that do not also couple with the stator windings. The reason for the name squirrel cage is because of the type of rotor used in these motors. 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.
The torque of a rotor in an induction motor under running condition is maximum. The rotor slot and rotor conductor has modified shape or modified peculiar shape can be draw or can be develop. Wound rotor induction motor the engineering projects. Some of the applications of this motor include cranes, mills, hoists and conveyors. Indirect vector control of multi cage induction motor. Then, the starting torque with increase but at the same time their will be more copper loss and %n of motor will decreases. The higher valued rotor resistance results more torque to be developed at the starting. Motors employing this type of rotor are known as squirrel cage inductionmotors.
The copper colored wires form the squirrel cage because they looks like one of those exercis. Whereas a synchronous motor s rotor turns at the same rate as the stator field, an induction motor s rotor rotates at a somewhat slower speed than the stator field. The starting torque of squirrel cage induction motor is low compared to the dc motor and the slip ring induction motor. The 3phase set of currents, each of equal magnitude and with a phase.
Sep 15, 2017 double cage induction motor is used for cage rotor to increase rotor resistance so higher starting torque can achieve by this method. Motors employing this type of rotor are variously known asphasewound motors or wound motors or as slipring motors. This arrangement is used for obtaining high starting torque at a low value of starting current. Pdf analytical modeling of double cage rotor induction motors in. Cage induction motor an overview sciencedirect topics. The starting torque could be increased by increasing starting resistance but due to high current in the rotor during starting will increase the copper loss which will decrease the motor. Wound rotor induction motors ac motors electronics textbook. Evaluation of the detectability of broken rotor bars for double squirrel cage rotor induction motors conference paper pdf available october 2010 with 3,334 reads how we measure reads. Double cage induction motor, cogging and crawling of induction motor, induction generator. The figure below shows a deep bar cage rotor with deep and narrow bars. Wound rotor induction motor is also used in fans, blowers and mixers. An induction motor with two cage rotor is used for high starting torque. Alternatively, the preferred flux paths can be imposed by removing iron inside the rotor so that the flux is.
Double cage rotor of an induction motor a double cage induction motor is that type of motor in which a double cage or two rotor windings or cages are used. An double cage induction motor is that type of motor in which a double cage or two rotor windings or cages are used. What are the merits and demerits of singlecage and double. The deep bar and double cage rotor are used to increase starting torque of squirrel cage induction motor. Jul 25, 2019 a 3 phase squirrel cage induction motor is a type of three phase induction motor which functions based on the principle of electromagnetism. Oct 09, 2016 a 3 phase induction motor has two types based on the rotor construction, named as. Are there any uses for double cage induction motors. There are two basic reasons for the use of singlephase motors rather than 3phase motors. Almost 95% of the induction motors used is of squirrel cage type. And in the previous article on types of electrical motors, we have classified induction motors based on the type of rotor used. The resistance of the upper cage winding is more than the inner c. As its name indicates stator is a stationary part of induction motor. The asynchronous machine block implements a threephase asynchronous machine wound rotor, single squirrel cage, or double squirrel cage.
How are squirrel cage induction motors constructed. An induction motor with two rotor windings or cages is used for obtaining high starting torque at low current. The stator of a double cage rotor of an induction motor is same as that of a normal induction motor. The simulation of double cage induction motor provides the base for the design of the. Squirrel cage rotor almost 90 per cent of induction motors are squirrel cage. The stator of a double cage rotor of an induction motor is same as that of a normal induction.
This simplest form of ac induction motor or asynchronous motor is the basic, universal workhorse of industry. A double cage induction motor is that type of motor in which a double cage or two rotor windings or cages are used. Analytical modeling of double cage rotor induction motors in healthy and broken bars conditions. Double cage rotor of an induction motor 6nq8vq6w61nw. However, it reduces substantially in a slipring motor due to the high impedance of the rotor circuit. The model of double cage induction motor for the analysis of thermal fields in transient operations article pdf available january 2017 with 1,335 reads how we measure reads. This rotor is a cylinder of steel laminations, with highly. The model may be repre sented by an equivalent single rotor. Sep 18, 2019 the deep bar and double cage rotor are used to increase starting torque of squirrel cage induction motor. Double cage and deep bar squirrel cage rotor induction motor. The model of doublecage induction motor for the analysis of.
Vibration signature analysis for rotor broken bar diagnosis. High during starting and low at normal operating speed. Slip ring induction motor is made up from wound rotor and squirrel cage induction motor is made up from the squirrel cage rotor. Wound rotor induction motors chapter ac motors pdf version. Pdf the model of doublecage induction motor for the. In practice, in order to convert temporarily the single phase motor into twophase motor, auxiliary conductors are placed in the upper layers of stator slots. Model the dynamics of threephase asynchronous machine.
Firstly, i am going to tell you about the structure of squirrel cage induction motor. Equivalent circuit of double cage induction motor the mathematical model of a double cage induction machine is arranged in a manner which is closely similar to the derivation of the d,q model of a single cage induction machine. Double cage rotor a rotor design, which though more expensive gives still better starting, and running performances than the deepbar design, is the doublecage rotor. Deep bar rotor the deep bar rotor in an induction motor is used to obtain high rotor resistance at starting and low rotor resistance at the running condition. Construction of squirrel cage induction motor explained. A double squirrel cage rotor is shown in the figure. Pdf the model of doublecage induction motor for the analysis of. Double cage induction motor is used for cage rotor to increase rotor resistance so higher starting torque can achieve by this method. The advantage of using sqim over other motors is that it does not have slip rings. When the rotor resistance is increased, so is the slip for maximum torque, and the stable operating slip range of the.
Double cage induction motor introduction diy electrical. 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. In this small post we will discuss about the double cage induction motor in brief. Starting performance as compare to double cage rotor, the single cage has less starting torque so at starting less heating loss occur. The mode of operation is dictated by the sign of the mechanical torque. The squirrel cage winding in this design consists of two layers of bars shortcircuited by end rings. As the name indicate the double cage induction motor has two winding in rotor. The outer cage bars have a smaller crosssectional area than the inner bars and are made of high resistivity materials like brass etc. It has been shown for example, in that the single cage model is not able to capture both the starting characteristics and the breakdown torque characteristics of a cage induction motor. For reason of economy, most houses, offices and also rural areas are supplied with single phase a. But the rotor construction differs with respect to the type of motor. In a slip ring induction motor, the rotor resistance is a.
Jan 02, 2020 in the squirrel cage induction motor, the rotor has very low fixed resistance, therefore, the starting torque is low due to low power factor and high reactance. Double cage rotors free download as powerpoint presentation. The slotting arrangement for double cage induction motor is as shown in above figure. In the squirrel cage induction motor, the rotor has very low fixed resistance, therefore, the starting torque is low due to low power factor and high reactance. Phasewound rotor this type of rotor is provided with 3phase, double layer, distributed winding consisting of coils.
Construction an induction motor with two cage rotor is used for high starting torque. The double cage rotor has two cages in which rotor winding is accommodated. Torque speed characteristics of induction motor slip. The resistance of the squirrel cage induction motor can not be varied as compared to the slip ring induction motor. Hello dipti, the term squirrel cage is a description of the rotor commonly found in an ac induction motor. In case of 3o squirrel cage motor has low starting torque. Squirrel cage induction motor and wound rotor induction motor. Working of double squirrel cage motor at starting of the motor, frequency of induced emf is high because of large slip slip frequency of rotor emf supply frequency. The starting of an induction motor does not relate to simple switching alone. A stator winding is placed in the stator of induction motor and the three phase supply is given to it. Due to the additional second cage, the rotor is now described with four differential.
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. It consists of a cylinder of steel laminations, with aluminum or copper conductors embedded in its surface. In this paper, a new diagnostic index that allows the extraction of rotor fault components issued from axial vibration signals, is defined to improve the fault quantification procedure. Emergency motor switchon happens occasionally while operating a double squirrelcage motor at full supply voltage with the rotor. A 3 phase induction motor has two types based on the rotor construction, named as. When the speed of the rotor of the deep bar double cage induction motor increases, the frequency of the induced emf and current in the rotor gets gradually decreased. The construction of stator of the induction motor is almost the same as other motors. 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. A squirrel cage rotor is the rotating part of the common squirrel cage induction motor.
Also the rotor bars are usually not quite parallel to the rotor shaft but are mounted in a slightly skewed position. Three phase squire cage induction motor, fully enclosed. The rotor will constantly be turning to align its magnetic field with that of the stator field. Squirrel cage induction motor the engineering projects. In double cage rotor there are two layers of bars as shown. A wound rotor induction motor has a stator like a squirrel cage induction motor, but a rotor with insulated windings brought out via slip rings and brushes. Dec 27, 2015 an induction motor with two cage rotor is used for high starting torque.
In both induction and synchronous motors, the ac power supplied to the motor s stator creates a magnetic field that rotates in synchronism with the ac oscillations. Stator of double cage induction motor is similar to the ordinary induction motor. Their sole purpose is to allow resistance to be placed in series with the. Now let us discuss in detail, the most common form of induction motor, the squirrel cage induction motor. Pdf evaluation of the detectability of broken rotor bars. It is usually designed for fixedspeed operation, larger ratings having such features as deep rotor bars to limit direct on line dol starting currents.
Jun 12, 2016 an induction motor with two cage rotor is used for high starting torque. The rotor therefore resembles a cage induction motor, with parts of the periphery cut away in order to force the flux from the stator to enter the rotor in the remaining regions where the airgap is small, as shown in fig. The outer bars consists of rotor bars having low reactance and high resistance. Control of motorcharacteristics by squirrelcage rotordesign. But the rotor consists of two windings or cages namely outer cage and inner cage.
When a 3 phase supply is given to the stator winding it sets up a rotating magnetic field in space. The double cage motor is so develop that it overcomes the above difficulties and given good starting torque with good efficiency for that purpose. Study of double cage induction motors with different rotor bar materials. Double cage rotor a rotor design, which though more expensive gives still better starting, and running performances than the deepbar design, is the double cage rotor. The stator of a double cage induction motor is similar to that of ordinary induction motor. Pdf emergency motor switchon happens occasionally while operating a doublesquirrel cage motor at full supply voltage with the rotor blocked e. The rotor bars are not insulated from the rotor core because they are made of metals having less resistance than the core. Advantage of double cage rotor over single cage rotor induction.
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