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Online Course

Electrical Machines - II

Indian Institute of Technology, Kharagpur and NPTEL via Swayam


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The course will begin with explaining basic underlying principles of working of various types of electrical rotating machines. The conditions to be fulfilled for the steady production of electromagnetic torque (Te).Motoring and generating mode of operation. Primary focus will be on the operation of 3-phase induction machine, single phase induction motor,and synchronous machines.A fair knowledge of distributed windings is essential in order to understand the working of rotating machines more effectively – few lectures will be devoted on this topic. Concept of electrical and mechanical angles will be explained.Nature of magnetic flux distribution along the air-gap of a rotating machine will be discussed.Clear concept of Rotating magnetic field is so important in understanding the operation of induction and synchronous machines.For each of this machine equivalent circuit will be derived and then used to derive expression for the torque. Starting, speed control and electrical braking of the motors will be discussed. Although main focus will be on the steady state performance analysis, few cases of important transient analysis will be discussed. Students will be motivated to solve numerical problems logically and efficiently.


Week 1  :  Brief review of transformer. Rotating machine :general constructional features. Conditions for steady production electromagnetic torque. Torque production can be explained in terms of interaction of two sets of magnetic poles – one produced by stator coil current and the other by rotor coil currents.
Week 2  :  MMF and flux density distribution along the air-gap of a rotating machine by a single coil and by multiple coils. Basic winding terms and elementary balanced 3-phase winding. Idea of electrical and mechanical angle.
Week 3  :   Production of rotating field by a 3-phase winding – iits speed and direction of rotation and its far reaching implications.
Week 4  :  The expression of induced voltage in a coil when it moves relativeto a field distribution – its rms value and frequency.
Week 5  : Types and constructional features of 3-phase induction motor. Slip and its importance. Development of equivalent circuit of the motor when it runs with a slip. Getting expression for torque in terms of equivalent circuit parameters and supply voltage.
Week 6  : Typical torque slip characteristic. Fixing operating point when load torque is present. Modification of the torque -slip characteristic by varying rotor resistance, supply voltage and frequency.
Week 7  :  Estimation of equivalent circuit parameters from no load and locked(blocked) rotor tests. Problem solving.
Week 8 :  Single phase induction motor: double revolving field theory and development of equivalent circuit and expression for torque..Torque-slip characteristic. Expression for starting torque in presence of auxiliary winding. Estimation of starting capacitance forauxiliary coil using concept of phase splitting.
Week 9 :  Synchronous machine: Types and constructional features . EMFequation and concept of synchronous reactance. Synchronising an incoming generator (alternator) to the bus. Phasor diagram as generator. Regulation. Effect of excitation variation when generatoris connected to bus. Power-angle characteristic. Steady statestabilty limit.
Week 10  :  Synchronous machine connected to bus and operating as motor .Phasor diagram under various operating conditions. Effect of excitation variation.
Week 11  :  Salient pole synchronous machine : concept of direct axis and quadrature axis reactances. Phasor diagrams under various operating conditions both for motoring and generating mode
Week 12  :  Swing equation under dynamic condition. Equal area criteria.Steady-state and transient stability limits.

Taught by

Prof.Tapas Kumar Bhattacharya

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