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Previous Year Exam Questions of Design of Electrical Machines of bput - DEM by Verified Writer

  • Design of Electrical Machines - DEM
  • 2017
  • PYQ
  • Biju Patnaik University of Technology Rourkela Odisha - BPUT
  • Electrical and Electronics Engineering
  • B.Tech
  • 4033 Views
  • 105 Offline Downloads
  • Uploaded 1 year ago
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Registration No: Total Number of Pages: 02 B.Tech. PEL5D001 5th Semester Regular Examination 2017-18 Electrical Machine Design BRANCH: EEE Time: 3 Hours Max Marks: 100 Q.CODE: B399 Answer Question No.1 and 2 which are compulsory and any four from the rest. The figures in the right hand margin indicate marks. Q1 a) Answer the following questions: multiple type or dash fill up type Maximum temperature limit for class B insulation is: a.105OC b.120Oc c.1300c d.1550c (2 x 10) b) Electrical machines having power output rating from a few KW up to about 250KW may be called the______ size machines. a. small b. medium c. large c) A Synchronous machine with longer air gap will have : a. low stability limits b. smaller unbalanced magnetic pull c. higher noise level d. poor ventilation d) Skewing of slots : a. improves heat transfer b. reduce noise c. suppresses the undesirable harmonics d. none of the above e) Power transformers are designed to have maximum efficiency at around ____full load a. nearly b.70% c.50% d.25% f) The most suitable material for transformer core is a. hot rolled grain oriented b. CRGOS C. cast steel aluminum g) The thickness of transformer core lamination is a. 3mm-5mm b..35mm- .5mm c.30mm-50mm d. copper d. d..035mm -.05mm h) A salient pole synchronous motor is fed from an infinite bus and is running at no load. Its field current is reduced to zero, then the motor would a .Stop b .Run at a reduce speed. C .Run at synchronous speed. d.Run at above synchronous speed. i) In an induction motor ,rotor input is 600 W and slip is 4% ,the rotor copper loss is a 700 W b 0.6 W c 650 W d 24 W j) Maximum temperature limit for class B insulation is: a.105OC b.120Oc c.1300c d.1550c

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Q2 Answer the following questions: Short answer type A transformer is working at its maximum efficiency. Its iron loss is 500W. Find the copper loss. Why the limbs are designed with stepped size of core type transformer ? What is the KVA rating for Oil natural cooling with tubes of a transformers ? Write the major application of synchronous motors. Why breather is provided in power transformer ? A 200/100V ,50 Hz transformer is to be excited at 40Hz from 100V side . For the same exciting current, what voltage is applied ? Find the %slip of an 4 pole , 50 hz induction motor running at 1400 rpm. How three phase induction motor is self starting?? What rating of a transformer is provided for air blast cooling ? Why open-circuit test on a transformer is done ? (2 x 10) a) Design a 50 VA step down transformer of 230V to 12V.. For designing a small transformer magnetic flux density is averagely taken as 1 to 1.2.Current . Te = 4 turns per volt.density of copper wire is taken as 2.2 A / mm2 to 2.4 A/ mm2 (approximately). (10) b) Why salient pole construction is rejected for turbo alternator ? what is short circuit ratio(SCR)? (5) a) Derive the output equation of a single phase transformer. (10) b) Describe the methods of cooling of transformers. (5) a) Design a 50 VA step down transformer of 230V to 12 V. For designing a small transformer magnetic flux density is averagely taken as 1 to 1.2.Current . Te = 4 turns per volt.density of copper wire is taken as 2.2 A / mm2 to 2.4 A/ mm2 (approximately). Derive the voltage per turn equation of a transformer. (10) a) Determine the main dimensions, no of stator slots and turns per phase of a 3.7 kW, three phase 400 v, 4 pole 50 hz squirrel cage IM given that flux density=0.45 wb/m2 .ampere conductor per meter of armature periphery=25000, full load efficiency=0.87, full load power factor=0.87, kw=0.95. take L/τ=1.45 (10) b) Discuss the factors to be considered in estimating the air gap length of induction motor. (5) a) Determine the main dimensions of a three phase alternator 100kVA, 375 rpm, 50 hz. The average air gap flux density=0.45 wb/m2.ampere conductor per meter=27000. Given L/τ =2.5.the peripheral speed is 50m/sec.the run away speed is 1.8 times the synchronous speed. (10) b) Derive the output equation of an AC machine. (5) a) Discuss the various steps to design the rotor of a squirrel cage induction motor. (10) b) Write notes on classifications of insulating materials. (5) a) Explain the steps to design the field winding of synchronous machine. (10) b) Describe the temperature rise as well as the cooling methods in transformers. (5) a) b) c) d) e) f) g) h) i) j) Q3 Q4 Q5 b) Q6 Q7 Q8 Q9 (5)

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