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- Design of Electrical Machines - DEM
- 2018
- PYQ
**Biju Patnaik University of Technology Rourkela Odisha - BPUT**- Electrical and Electronics Engineering
- B.Tech
**424 Views**- 2 Offline Downloads
- Uploaded 10 months ago

Registration No : Total Number of Pages : 02 B.Tech PEL5D001 5th Semester Regular Examination 2018-19 ELECTRICAL MACHINE DESIGN BRANCH : EEE Time : 3 Hours Max Marks : 100 Q.CODE : E563 Answer Question No.1 (Part-1) which is compulsory, any EIGHT from Part-II and any TWO from Part-III. The figures in the right hand margin indicate marks. Q1 a) b) c) d) e) f) g) h) i) j) Q2 a) b) c) d) e) f) g) h) i) j) k) l) Part- I Short Answer Type Questions (Answer All-10) A transformer is working at its maximum efficiency .Its iron loss is 800W. Then what will be its copper loss if the load is half. What is the value of dielectric strength of transformer oil and air? How the dielectric strength of the transformer oil gets detoriate and how to regain its strength. How does the role of air gap in a Synchronous machine help better performance? What is the KVA capacity limit of Air blast cooling transformers? What the use of comploes in DC machines. What is the Maximum temperature limit for class B insulation? Differentiate between Power transformers and distribution transformers. What is the rotor speed of an induction motor with slip 4%? Why the transformers have efficiency more than the motors?? Part-II Focused-Short Answer Type Questions- (Answer Any Eight out of Twelve) Design a 4 -pole simplex lap winding suitable for an armature of 20 slots. Consider single turn coil with two conductors per slot. The transformer has 800 watts of full load losses. What will be its loss at ¾ th of full load? Write the applications of the lap and wave winding in various machines. Describe the methods of cooling of transformers State and explain the main factors which influence the choice of specific electric loading. Find the %slip of an 4 pole, 50 Hz induction motor running at 1400 rpm . If a transformer is designed for 50 Hz is connected to a 25 Hz system, what happens? A four pole, simplex lap wound armature contains 16 slots having 2 coil sides per slot. Find back pitch and front pitch for retrogressive winding. An 8 pole, 240 v, simplex lap wound armature develops 120 amp. Determine the voltage per path current per brush. Justify that the selection of material for designing a filed system depends upon hysteresis loop . What are double cage induction motors? If synchronous motor is made to run at over excited condition, for what purpose it can be used? (2 x 10) (6 x 8)

Q3 Q4 Part-III Long Answer Type Questions (Answer Any Two out of Four) 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). 300 KVA, 3 phase, 50Hz, 1100 V, 370 rpm synchronous generator with a concentric winding has the following design data (16) (16) Specific magetic loading Bav = 0.58 wb/m2,Specific electric loading ac = 32,000 A/m Gap length = 4.5 mm; field terms per pole = 60; short circuit ratio = 1.18. the efficiency gap area is 0.6 times the actual area. Peripheral speed is 35m/s. Find stator core length, turns per phase mmf for airgap, armature mmf per pole and field current for no load and rated volts. Q5 Design a separately excited DC shunt . motor 240v, 75kW,100rpm, 4 pole machine with class B insulation.(shaft height is 400 mm) .Take efficiency 0.89. the sp. Loading is 0.5 wb/m2.take AC=35,000Nm.Ψ=0.67. (16) Q6 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/m 2 .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 (16)

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