The starting torque and the starting periods is also large. If an induction machine with closed or skewed rotor slots is studied, the model for saturation should be extended. This includes the starting and running values of the rotor single cage equivalent circuit. Introduction as stated in prior research l, 2, while starting up the deep bar and double squirrel cage.
The deep bar and double cage rotor are used to increase starting torque of squirrel cage induction motor. Cracking or breaking these bars arises due to manufacturing problem on the bar itself or due to high value of. More emphasis should be put on the acquisition of an in. Oct 04, 2017 as the motor speeds up, the rotor frequency decreases and the current distributes in both the cages of the double cage rotor or in the complete bar in the deep bar rotor. Double cage induction motor introduction diy electrical. Double cage induction motor is used for cage rotor to increase rotor resistance so higher starting torque can achieve by this method. Both deep bars and double cage structures 123 4 have the same effects. Based on the influence of the skin effect over electrical rotor parameters can be constructed a mathematical mode. Pdf skin effect modelling in induction motors rotor deep bars. Study of double cage induction motors with different rotor bar. The double cage behaves like a deep bar cage electric equipment. As the name indicates, the double cage induction motors have two cages in the rotor and they have the advantages of both squirrelcage induction motors and wound rotor induction motors. High during starting and low at normal operating speed b. Deep bar rotor the chief advantage of the slipring induction motor compared to the squirrel cage one lies in the fact that while its rotor is designed with low resistance to give good running performance high efficiency, low slip, etc.
Can any body advise me of a straightforward method of converting these parameters to the resistance and reactance of a double cage induction motor, which has a torque speed curve similar to that of the deep bar machine. For a double cage rotor, the same rule as above applies. The stator of a double cage induction motor is similar to that of ordinary induction motor. Now that you know some of the design characteristics of the double cage rotor, are there any special considerations that should be given for testing. Double cage induction motor electrical engineers guide. Let us refresh the advantages of squirrel cage induction motor and wound rotor induction motors. The squirrel cage winding in this design consists of two layers of bars shortcircuited by end rings. Remains same during starting and normal operating speed d. In this paper, for higher frequencies some analytic expressions are proposed, that result from the skin effect theory. The squirrel cage with deep rotor bar can be equivalent with a double cage, one of these cages being with constant parameters 8. The model of doublecage induction motor for the analysis.
Also appreciate the rugged construction of squirrel cage rotor and know the spectacular reasons for the skewed arrangements of the rotor conductors. On the other hand, the inner cage consists of rotor bars having high reactance and low resistance. The double cage rotor has two cages in which rotor winding is accommodated. An induction motor model with deepbar effect and leakage. Figure 727a shows a current flowing through the upper part of a deep rotor bar. Output parameters of single cage and double cage rotor parameters single cage rotor double cage rotor starting torque, t st nm 4. Double cage rotor a rotor design, which though more expensive gives still better starting, and running performances than the deep bar design, is the double cage rotor.
Indirect vector control of multi cage induction motor. The double cage behaves like a deep bar cage electric. Hence the inductive reactance x l in the inner side bars or deep bars gets decreased and the current faces less inductive reactance and less resistance as a whole. Request pdf study of double cage induction motors with different rotor bar. Due to this reason, the cost of the motor is quite low. Based on the influence of the skin effect over electrical rotor parameters can be constructed a mathematical model for the asynchronous motor with deep rotor bar, that allows simulation of. Pdf the model of doublecage induction motor for the. Construction an induction motor with two cage rotor is used for high starting torque. The squirrelcage winding in this design consists of two layers of bars shortcircuited by end rings. The sliptorque curve for deep bar rotor is shown below along with the deep bar stator. Nov 18, 2015 the double cage rotors use deep rotor bars, as illustrated in fig. Slip ring rotor for both of them the stator part connection is same.
Control of motor characteristics by cage rotor design. 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. More emphasis should be put on the acquisition of an inrushstartup test as a baseline. 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. Novel method of improving squirrel cage induction motor. Double cage rotor of an induction motor rotor resistance control of an induction motor. Dynamic modelling of induction motor squirrel cage for. The rotor parameters, the resistance and the leakage inductance, vary with the currents frequency of rotor bars due to skin effect, and for small frequencies can be negligible under 10 15 hz. Hence, the induction machine is a doubly excited machine in the same sense as the synchronous and dc machines. May 02, 2016 before answering the question we have to know about types of rotors in induction motors. This paper deals with deep bar effect in squirrel cage rotors.
Mar 15, 2020 a squirrel cage induction motor does not contain brushes, slip rings and commutators. In deep bar double cage rotor bars are there in two layers. In pdmas january 5 tip, the company discussed what a doublecage rotor is. On the other hand, the rotor current mainly flows in the symmetric inner cage under steady state operating condition, and fault signature is insensitive to outer cage damage.
The doublecage rotors use deep rotor bars, as illustrated in fig. For the low starting torque requirements, an ordinary cage motor is used. Double cage rotor of an induction motor 6nq8vq6w61nw. 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. Mar 25, 2017 consequently, at high slip frequency, the rotor current resides mainly in the upper starting cage while, at low slip frequency, the current flows mainly into the working lower cage. While the constant parameter model of a double cage machine is well known 24, no attempt has been made so far to develop an appropriate model of a saturated dou ble cage induction machine. Control of motorcharacteristics by squirrelcage rotordesign. The outer bars consists of rotor bars having low reactance and high resistance. The squirrel cage with deep rotor bars can be equivalent with a double cage, one of these cages having constant parameters 8.
Induction machines using this type of rotor are widespread. 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. Double cage rotors free download as powerpoint presentation. As the motor speeds up, the rotor frequency decreases and the current distributes in both the cages of the double cage rotor or in the complete bar in the deep bar rotor. Construction of squirrel cage induction motor explained.
Dec 26, 2015 what is meant by double cage induction motor. The resulting models can be applied with some degree of approximation to induction machines with deepbar rotor as well. The skin effect is mostly relevant in the case of deep rotor bars and a doublecage structure. Low at starting and high at normal operating speed c. The resistance of the upper cage winding is more than the inner c. 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. 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. Skin effect modelling in induction motors rotor deep bars. Deep bar or double cage rotors are used in squirrel cage. The advantages of squirrel cage and wound rotor induction motors are combined in the double cage induction motor.
Pdf analytical calculation of equivalent circuit parameters. The stator of a double cage rotor of an induction motor is same as that of a normal induction motor. A squirrel cage induction motor does not contain brushes, slip rings and commutators. This arrangement is used for obtaining high starting torque at a low value of starting current. It is seen that the top most layer element a is linked with minimum leakage flux and therefore its leakage inductance is minimum. A bar may be assumed to be made up of number of narrow layers as shown in fig. Representation of the rotor with two rotor windings rather than with a single winding is known to lead to significant improvement in the accuracy of simulation results for both deep bar and double cage induction machinesl. The basic concept is illustrated with a deepbar rotor in figure 727.
Select current density in rotor bars and end rings depends on ambient temp, cooling conditions, and duty cycle, and from rotor bar and end ring currents get their cross sectional areas. The rotor of of an induction motor can be designed in two types. Deepbar cage rotor figure below shows a cage rotor with deep and narrow bars. Cracking or breaking these bars arises due to manufacturing problem on the bar itself or due to high value of bar currents which induce through rotor circuits. How are squirrel cage induction motors constructed. Before answering the question we have to know about types of rotors in induction motors.
Any machine with a deepbar rotor can be treated for modelling purposes as a doublecage induction machine 24. Introduction as stated in prior research l, 2, while starting up the deepbar and doublesquirrelcage. Sep 18, 2019 the deep bar and double cage rotor are used to increase starting torque of squirrel cage induction motor. Some cages enhance the deep bar effect to improve the starting performances. The sliptorque curve for deepbar rotor is shown below along with the deepbar stator. The model of doublecage induction motor for the analysis of. Performance analysis of three phase squirrel cage induction. Vibration signature analysis for rotor broken bar diagnosis. For higher torque requirements a deep bar cage motor is used. Need for deepbar and doublecage rotor deepbar rotors torqueslip relationship doublecage rotors equivalent circuit diagram. Know about the most popular and almost unbreakable construction of squirrel cage induction motor.
It is possible to produce a variable rotor resistance by the use of deep rotor bars or doublecage rotors. Starting torque is directly proportional to the rotor resistance. Deep bar cage rotor figure below shows a cage rotor with deep and narrow bars. July, 2018 3 of 11 the rotor receives its excitation by induction from the armature field. This kind of rotor consists of a cylindrical laminated core with parallel slots for carrying the rotor conductors, which are not wires, as we think, but thick, heavy bars of copper or aluminium aluminium or its alloys.
Apr 17, 2015 the sliptorque curve for deep bar rotor is shown below along with the deep bar stator. This is because an equivalent doublecage machine can always be found with an admittance locus closely fitting to that of a deepbar induction machine 18. A double cage induction motor is that type of motor in which a double cage or two rotor windings or cages are used. 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. A combined use of current and vibration analysis was developed.
Smallsignal model for saturated deepbar induction machines. Modelling of deepbar and doublecage selfexcited induction. Double cage equivalent of deep bar rotor motor electric. The slotting arrangement for double cage induction motor is as shown in above figure.
As stated in prior research l, 2, while starting up the deep bar and double squirrel cage motors with soldered rotors, the squirrel cag e winding is the component most vulnerable to damage. The effective resistance is small and running performance is improved. The advantages of squirrelcage and wound rotor induction motors are combined in the double cage induction motor. Sem08 deep bar cage rotor induction motor duration. Ac motors, heating, induction motors, squirrel cage motors, temperature rise 1. Due to the absence of brushes, there are no sparks in the motor. Threephase induction 208v motor with matlab revised. An induction motor with two rotor windings or cages is used for obtaining high starting torque at low current.
However, slip rings are used in wound type induction motor to add external resistance to the rotor winding. Class b has large and deep rotor bars, that is, the skin effect cannot be neglected during startup. Double cage and deep bar squirrel cage rotor induction. Speed control of induction motor induction motor speed control by pole changing. 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. 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. A woundrotor motor can be used for very severe starting conditions or when speed control by rotor resistance is required. Classes a and b have similar torquespeed characteristics. In a slip ring induction motor, the rotor resistance is a. As the name indicate the double cage induction motor has two winding in rotor.
Pdf electric machines by dp kothari and ij nagrath pdf. Torque speed characteristics of induction motor slip power. The figure below shows a deep bar cage rotor with deep and narrow bars. Advantage of double cage rotor over single cage rotor.
Another phenomenon that is usually omitted within the smallsignal analysis is the skin effect of rotor bars. Representation of the rotor with two rotor windings rather than with a single winding is known to lead to significant improvement in the accuracy of simulation results for both deepbar and doublecage induction machinesl. The dq modeling, order reduction and numerical analysis. Know about the different winding slots, lamination of the stator and its construction. The output parameters of the single and the double cage rotor induction motor are shown in table 2 table 2. Designing squirrel cage rotor slots with high conductivity. As stated in prior research l, 2, while starting up the deepbar and doublesquirrelcage motors with soldered rotors, the squirrel cag e winding is the component most vulnerable to damage. Thus both r be and x be vary with slip frequency as they do in a deep bar single cage figure 9. Abstractthis paper presents a dynamic modelling of a series of induction motors im squirrel cage with di. Broken rotor bar faults these common faults occur on the movement part of cage rotor type or synchronous machine, which has damper bars. The leakage inductance is small in this region due to the tight coupling between the rotor and the stator. What are the merits and demerits of singlecage and double.
While the constant parameter model of a doublecage machine is well known 24, no attempt has been made so far to develop an appropriate model of a saturated dou. Since current flowing in that area is tightly coupled to the stator, the leakage. Any machine with a deep bar rotor can be treated for modelling purposes as a double cage induction machine 24. Advantages and disadvantages of induction motor electrical4u. Deep bar or double cage rotors are used in squirrel cage induction motor to obtain published on 27 oct 15. The conductor bars are inserted from one end of the rotor and as one bar in each slot. Consequently, at high slip frequency, the rotor current resides mainly in the upper starting cage while, at low slip frequency, the current flows mainly into the working lower cage. When the rotor is stationary or turnin g slowly the frequency of rotor currents is relatively high, the currents crowd to the top of the rotor bar and the resistive part of impedance is relatively high.
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