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Static Drives Lecture Notes

MODULE-I (10 HOURS) Requirements, AC and DC drives, modern trends in drives technology, Characteristics of DC, Induction and Synchronous motor drives, (starting, running, speed control, braking), size and rating of motors (short time, intermittent, continuous), Mechanical considerations (enclosure, bearing transmission of drive, through chain, pulley and gears noise) . MODULE-II (10 HOURS) Control for drive systems, Control of D.C, Induction, and Synchronous motor drives. Control Techniques for electric drives, Block diagram representation, transfer functions, transient response, frequency response and stability, compensating techniques. MODULE-III (10 HOURS) Electric Traction: System of electric traction Mechanics of Train Movement: Speed- time, distance- time and simplified speed-time curves, Attractive effort for acceleration and propulsion, effective weight, train resistance, adhesive weight, specific energy output and consumption. Traction Motors: Review of characteristics of different types of DC and AC motors used traction and their suitability MODULE-IV (10 HOURS) Rating and heating of electric drives, power loss, Heating and cooling of motors, Classes and duty and selection of motors, Drives for specific application like steel, paper, Textile Mills control of electric drives microprocessor hardware and software for drive system. REFERENCE BOOKS [1] V.Subrahmanyam, “Electric Drives” , TMH publication [2] M.H.Rashid , “Power Electronics” , P.H.I. Edition [3] G.K.Dubey, “Electric Drive”, Norasa Pub. House ND [4] Austin Hughes, “Electrical motors and drives, Fundamental, Types and Application” Newnes publication [5] S.K.Pillai , “A First Course on Electrical Drives”,2nd Edition, John Wiley & Sons

MODEL QUESTION-1 TIME: 3 Hours FM: 70 Answer any Six questions including Q.No.1 which is compulsory. 1. Answer all the following questions. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) [2×10] Write four advantage of an electric drive system. Draw the typical torque-speed characteristics of mechanical loads. What is a Group Electric Drive (Shaft Drive)? What is meant by “load equalization? Why stator voltage control is more suitable for speed control of induction motor in fan type load than constant type load ? A train driven by separately excited dc motors has better co-efficient of adhesion than driven by series motor. Justify the statement. Compare static Kramer and Scherbius drive system. Draw the simplified speed/time curve for the main line services and show all necessary periods. What is self control of synchronous motor ? A 440 V, 60 Hz induction motor is to be used on a 50 Hz supply. What voltage should be used? 2. a) Why flywheel is mounted on the shaft of the motor in non-reversible drive? Deduce the expression for the Moment of Inertia of the flywheel. [4] b) A motor has a heating time constant of 45 minutes and cooling time constant of 75 minutes. The motor has final steady state temperature rise of 500C while delivering its continuous rating of 25 kW i) Determine the load the motor can deliver for 15 minutes so that the temperature rise does not exceed 500C. ii) The motor delivers 35 kW for a period of 15 minutes followed by a shutdown for 15 minutes. Determine the maximum temperature rise. [6] 3. a) Why braking is required ? Explain each of the electrical braking briefly. b) A 220 V, 1500 rpm, 11.6 A separately excited motor is controlled by a l-phase fully-controlled rectifier with an ac source voltage of 230 V, 50 Hz. Enough filter inductance is added to ensure continuous conduction for any torque greater than 25 percent of rated torque, Ra = 2 ohm i) What should be the value of the firing angle to get the rated torque at 1000 rpm? ii) Ca1culate the firing angle for the rated braking torque and - 1500 rpm. iii)Ca1culate the motor speed at the rated torque and = 160o for the regenerative braking in the second quadrant. [4+6] 4. a) Explain with sketch how the rheostatic braking is done in D.C. shunt and series motors [4]

b) The switching frequency of the chopper is 2 kHz. The source voltage is 80V and the duty ratio is 30%. The load resistance is 4 ohm. Assume that the inductance and capacitance are ideal and large enough to sustain the load current and load voltage with little ripple. Calculate i) On time and switching period ii) Average voltage across the load iii) Average current of the load [6] 5. a) Formulate the expression for the tractive effort during acceleration period of a locomotive train. b) Explain the speed control of induction motor by stator voltage/hertz control method. [5+5] 6. a) The distance between two stations is 1.92kms.The scheduled speed and the duration of stops respectively are 40kmph and 20sec. Assume the quadrilateral approximation of the speed-time curve and the coasting and braking retardation as 0.16kmphps and 3.2kmphps respectively. Determine the acceleration if the speed at the end of the accelerating period is 60.8kmph.Find also the duration of the coasting period. [6] b) Sketch and explain the static Kramer’s variable speed drive system [4] 7. a) How the operation of synchronous motor shifts from motoring to generative braking ? b) Draw the speed-torque characteristics of a three phase induction motor in its 4-quadrant region. [5+5] 8. Write short notes on the following (Any two) [5x2] a) Steady state stability of an electric drive b) Static Ward-Leonard Drive System c) Speed control by D.C. Chopper

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