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Government Engineering College, Bharuch
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Electrical Engineering Department
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Branch : Electrical
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Semester : 7th
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Course : AC Machines Design Code (GTU) : 3170909
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MID-SEMESTER TEST , SYLLABUS for
A C Machine Design(3170909)(7Th Semester- Electrical)

(1)Introduction
Major considerations in electrical machine design, Electrical engineering materials, Space
factor, Choice of specific electrical and magnetic loadings, Thermal considerations, Heat
flow, Temperature rise, Rating of machines.
(2) Design of transformers
Sizing of a transformer, Main dimensions, kVA output for single- and three-phase
transformers, Window space factor, Overall dimensions, Operating characteristics,
(3) Design of induction motors
Sizing of an induction motor, Main dimensions, Length of air gap, Rules for selecting rotor
slots of squirrel cage machines, Design of rotor bars & slots, Design of end rings, Design of wound rotor, Magnetic leakage calculations, Leakage reactance of poly phase machines, Magnetizing current, Short circuit current,
(4) Design of synchronous machines
Sizing of a synchronous machine, Main dimensions, Design of salient pole machines, Short
circuit ratio and its significance, Shape of pole face, Armature design, Armature parameters, Estimation of air gap length, Design of rotor, Design of damper winding,
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Year of Study : (ODD TERM)
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Question bank
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1Derive an output equation for 3-ф induction motor with usual notation.
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2Write a short note on Harmonic induction torque and Harmonic synchronous torque of squirrel cage induction motor Also give its effect on the selection rotor slots.
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3Explain the points to be considered for the selection of number of stator slots of an 3- phase induction motor.
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4Explain the factors that effects the choice of specific magnetic & electric loading in case of a induction machine.
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5Explain the factors that effects the choice of specific magnetic & electric loading in case of a synchronous machine.
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6Write the steps and necessary equations for rotor design of an synchronous machine
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7Define SCR and its importance in designing of synchronous machine.
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8State the rules for selecting rotor slots of an 3-phase induction motor. Also explain the methods for the reduction of harmonic torque.
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9Explain the current distribution in the bars and the end rings of a squirrel cage induction motor. Also derive the relation for the current in the end ring.
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10Discuss the Methods to reduce the harmonic torque in induction motor
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11Explain the factors which are to be considered while selecting the armature slots of a synchronous machine.
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12Discuss the effect of air gap length on the performance of a 3-phase induction motor.
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13Derive the equation of rotor resistance referred to stator side, for a squirrel cage induction motor.
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14Explain is the role of damper winding in (i) synchronous generator (ii) synchronous motor.
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15Discuss in steps the design of field winding of a salient pole synchronous machine.
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16Discuss the design differences of a salient pole and non salient pole synchronous machines.
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17Discuss the advantages achieved on selecting larger air gap in a three phase induction motor.
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18Discuss how the magnetizing current can be estimated from the design data in a three phase induction motor.
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19Explain the factors to be considered while selecting number of armature slots in the design of a synchronous machine.
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20Explain the design of salient pole rotor in a synchronous machine.
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21Write short note on “Influence of short circuit ratio on performance of synchronous machine.”
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22Discuss the effect of variation of main dimension(D&L) on performance (Rating, losses & efficiency) of 3-ф induction motor
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23List the factors affecting the length of air gap.
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24Discuss the different types of stator slots used in 3-ф induction motor
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25Discuss the Harmonic induction torque in 3-ф induction motor
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26Discuss the Harmonic synchronous torque in 3-ф induction motor
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27Discuss the Harmonic vibration torque in 3-ф induction motor
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28Prove that torque produce by 5TH harmonics is in backward direction & 7TH harmonics is in forward direction.
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29State the rules for the selection of rotor slots. Describe the methods for reducing the effect of harmonics torque.
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30Explain SCR and its effect on synchronous machine performance.
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31Explain the deciding factor for stator slots and state the equation for 1) Area of stator slots 2) Stator winding resistance 3) Stator copper losses
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32Explain steps of design of field winding of alternator.
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33Explain importance of damper winding in synchronous machine.
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34Explain the factors affecting the selection of Air gap of three phase Induction Motor.
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35Explain the terms “critical speed” and “run away speed” with reference to synchronous machine.
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36State and discuss the factors to be considered while determining the air gap in case of 3- phase induction motors.
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37Draw and explain briefly the current distribution wave form spreaded over one pole pitch in bars and end rings squirrel cage induction motor.
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38Define and explain the term “short circuit ratio” of a synchronous generator and discuss its influences on the machine performance.
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39Explain the effect of skewing the rotor slots in a squirrel cage induction motor.
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40What is the role of damper winding in (i) synchronous generator and (ii)synchronous motor? Derive the equation of MMF of damper winding.
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41Derive equation Et = k √Qwhere Q = kVA rating of a transformer. Explain how service condition of transformer affect the value of K.
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42Answer the following questions with respect to transformer design. (Be brief and to the point).
(1) Explain the reason for using stepped core construction.
(2) If a designer selects higher value of flux density what will be its effect on performance and cost of the transformer?
(3) Why tapings are usually provided on the h.v. winding side?
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43Define : (1) Window space factor (2) Stacking factor.
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44Discuss the importance of mitred joints in the core assembly of transformers.
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45Derive the output equation of a 3-phase core type transformer.
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46What is window space factor? Explain how it varies with (i) KVA rating and (ii) KV rating.
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47Explain the steps involved to calculate no load current of a 3-phase transformer from its design data.
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48Answer the following in respect to transformer design:
(i) Why cores are stepped?
(ii) Why yoke is designed for low flux density?
(iii) Why circular coils are preferred in transformer winding?
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49Explain in brief the factors affecting the value of K in the expression of volt per turn in transformer design.
Et = K _ KVA
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50Explain technical reasons for :
(1) Low flux density is selected for yoke of a three phase transformer.
(2) Circular coils are preferred in transformer winding.
(3) Tappings are usually provided on h.v. side of transformer.
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51Explain the constructional features of the transformer.
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52Derive the output equation of 1φ core-type and shell-type transformers.
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53 Derive the output equation of 3φ core-type and shell-type transformers.
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54Obtain the expression for ratio of gross core area to circumscribing circle’s area for (a) square core and (b) stepped core.
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55Derive an output equation for 3-ф synchronous machines with usual notation.
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