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The three-phase induction motors are the most widely used electric motors in industry. They run at essentially constant speed from no-load to full-load. However, the speed is frequency dependent and consequently these motors are not easily adapted to speed control.
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- Disclaimer
- SYLLABUS/ TOPICS COVERED
- (b) Rotor Construction
- (a) Stator Construction
- 3.3 Principle of Operation
- 3.5.3 Slip
- 3.5.4 Rotor Current Frequency
- 3.10 Rotor Output
- 3.12 Circle Diagram
- 3.12.2 Tests to Determine the Equivalent Circuit Parameters
- 1. No-load test
- 2. Blocked-rotor Test
- 3.13 Performance Characteristics of Three phase Induction Motor
- 3.15.1 Methods of Starting Three Phase Induction Motors
- 3.16 Speed control of Three Phase Induction Motors
- 3.16.4 Pole changing method
- 3.16.5 Stator frequency control
- 3.17 Power Stages in an Induction Motor
- Fixed losses
- 3.18 Double Cage Induction Motor
- Cogging (Magnetic Locking or Teeth Locking) of induction motor
- Induction Generator Application
- SYLLABUS/ TOPICS COVERED
- 4.1.1 Double Revolving Field Theory of Single Phase Induction Motor
- 1- The DC Test:
- 4.3.1 Working of Split Phase Motor
- 4.4 Single Phase Series Motor
- 4.4.1 Operation
- 4.4.3 Applications
- Advantages:
- 4.5.6 Applications
- 4.6.3 Applications
- Acknowledgement
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This document does not claim any originality and cannot be used as a substitute for prescribed textbooks. The information presented here is merely a collection by the committee members for their respective teaching assignments. Various sources as mentioned at the end of the document as well as freely available material from internet were consulted ...
Three Phase Induction Motors: Types, Construction and principle of operation, 3 phase Induction Motor, general phasor diagram, equivalent circuit, power and torque relations, condition for maximum torque, circle diagram, Performance characteristics, effect of rotor resistance on speed torque characteristics, stable & unstable region of operation, O...
The rotor of the squirrel cage motor shown in Fig: 3.1(b) contains no windings. Instead it is a cylindrical core constructed of steel laminations with conductor bars mounted parallel to the shaft and embedded near the surface of the rotor core. These conductor bars are short circuited by an end rings at both end of the rotor core. In large machines...
The construction of the slip ring induction motor is exactly similar to the construction of squirrel cage induction motor. There is no difference between squirrel cage and slip ring motors.
The operation of a 3-phase induction motor is based upon the application of Faraday Law and the Lorentz force on a conductor. The behaviour can readily be understood by means of the following example. Consider a series of conductors of length l, whose extremities are short-circuited by two bars A and B (Fig.3.3 a). A permanent magnet placed above t...
We have seen above that rotor rapidly accelerates in the direction of rotating field. In practice, the rotor can never reach the speed of stator flux. If it did, there would be no relative speed between the stator field and rotor conductors, no induced rotor currents and, therefore, no torque to drive the rotor. The friction and windage would immed...
The frequency of a voltage or current induced due to the relative speed between a vending and a magnetic field is given by the general formula; (ii) As the rotor picks up speed, the relative speed between the rotating flux and the rotor decreases. Consequently, the slip s and hence rotor current frequency decreases.
If there were no copper losses in the rotor, the output would equal rotor input and the rotor would run at synchronous speed Ns. It is clear that if the input power to rotor is “Pr” then “s.Pr” is lost as rotor Cu loss and the remaining (1 - s) Pr is converted into mechanical power. Consequently, induction motor operating at high slip has poor effi...
To analyse the three phase induction motor performance using circle diagram we need to determine the equivalent circuit parameters of the machine.
In order to find values for the various elements of the equivalent circuit, tests must be conducted on a particular machine, which is to be represented by the equivalent circuit. In order to do this, we note the following. When the machine is run on no-load, there is very little torque developed by it. In an ideal case where there is no mechanical ...
The behaviour of the machine may be judged from the equivalent circuit of Fig: 3.16 (a). The current drawn by the machine causes a stator-impedance drop and the balance voltage is applied across the magnetizing branch. However, since the magnetizing branch impedance is large, the current drawn is small and hence the stator impedance drop is small c...
In this test the rotor is prevented from rotation by mechanical means and hence the name. Since there is no rotation, slip of operation is unity, s = 1. The equivalent circuit valid under these conditions is shown in Fig: 3.16 (b). Since the current drawn is decided by the resistance and leakage impedances alone, the magnitude can be very high when...
The equivalent circuits derived in the preceding section can be used to predict the performance characteristics of the induction machine. The important performance characteristics in the steady state are the efficiency, power factor, current, starting torque, maximum (or pull-out) torque.
The method to be employed in starting a given induction motor depends upon the size of the motor and the type of the motor. The common methods used to start induction motors are: Direct-on-line starting Stator resistance starting Autotransformer starting Star-delta starting Rotor resistance starting Methods (i) to (iv) are applicable to both squi...
The induction machine, when operating from mains is essentially a constant speed machine. Many industrial drives, typically for fan or pump applications, have typically constant speed requirements and hence the induction machine is ideally suited for these. However, the induction machine, especially the squirrel cage type, is quite rugged and has a...
Sometimes induction machines have a special stator winding capable of being externally connected to form two different number of pole numbers. Since the synchronous speed of the induction machine is given by ns = fs/p (in rev. /s) where p is the number of pole pairs, this would correspond to changing the synchronous speed. With the slip now corresp...
The expression for the synchronous speed indicates that by changing the stator frequency also it can be changed. This can be achieved by using power electronic circuits called inverters which convert dc to ac of desired frequency. Depending on the type of control scheme of the inverter, the ac generated may be variable-frequency-fixed-amplitude or ...
The input electric power fed to the stator of the motor is converted into mechanical power at the shaft of the motor. The various losses during the energy conversion are:
Stator iron loss Friction and windage loss The rotor iron loss is negligible because the frequency of rotor currents under normal running condition is small.
One of the advantages of the slip-ring motor is that resistance may be inserted in the rotor circuit to obtain high starting torque (at low starting current) and then cut out to obtain optimum running conditions. However, such a procedure cannot be adopted for a squirrel cage motor because its cage is permanently short-circuited. In order to provid...
Sometimes, the rotor of a squirrel cage induction motor refuses to start at all, particularly if the supply voltage is low. This happens especially when number of rotor teeth is equal to number of stator teeth, because of magnetic locking between the stator teeth and the rotor teeth. When the rotor teeth and stator teeth face each other, the reluct...
As energy costs so high, energy recovery became an important part of the economics of most industrial processes. The induction generator is ideal for such applications because it requires very little in the way of control system or maintenance. Because of their simplicity and small size per kilowatt of output power, induction generators are also fa...
Three Phase Induction Motors: Types, Construction and principle of operation, 3 phase Induction Motor, general phasor diagram, equivalent circuit, power and torque relations, condition for maximum torque, circle diagram, Performance characteristics, effect of rotor resistance on speed torque characteristics, stable & unstable region of operation, O...
Consider two magnetic fields represented by quantities OA and OB of equal magnitude revolving in opposite directions as shown in fig: 4.1. Fig: 4.2 (b) The resultant of the two fields of equal magnitude rotating in opposite directions is alternating. Therefore an alternating current can be considered as having two components which are of equal in...
The DC resistance of the stator can be measured by applying DC current to the terminals of the main winding and taking the reading of the voltage and the current (or using ohmmeter) and determine the DC resistance as follows: Then, the AC resistance is given by:
In split phase motor two windings named as main winding and starting winding are provided. At the time of starting, both the main and starting windings should be connected across the supply to produce the rotating magnetic field. The rotor is of a squirrel cage type and the revolving magnetic field sweeps part the stationary rotor, inducing emf in ...
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
A PDF document covering the topics of three phase induction motors, starting methods, speed control and single phase induction motors. Includes diagrams, equations, examples and references for B-Tech 4th SEM EE & EEE students.
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A three phase induction motor consists of three phase winding as its stationary stator. The three phase stator winding is connected in star or delta. The three phase windings are displaced each other by 120°. The windings are supplied by a balanced three phase a.c. supply.
A PDF document that provides detailed information on the design, installation, commissioning, operation and maintenance of a three-phase induction motor. It includes safety warnings, technical data, fault diagnosis, service and repair instructions, and an exploded view of the motor.
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Explain how a three-phase induction motor operates. Compute the synchronous speed of an induction motor and the slip between motor rotor and stator magnetic field. Compute the power that crosses that air gap of an induction motor.
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It can hurt to tangle with a three-phase motor. A successful salesman for General Electric's motor division once remarked to one of your instructors that, when asked by a customer how a motor
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In this chapter, the development of the model of a three-phase induction motor is examined starting with how the induction motor operates. The derivation of the
