Subject Code: 2170909
GUJARAT TECHNOLOGICAL UNIVERSITY
--- Content provided by FirstRanker.com ---
BE - SEMESTER-VII (NEW) EXAMINATION - WINTER 2018Subject Name: Design of AC Machines
Time: 10:30 AM TO 01:30 PM
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
--- Content provided by FirstRanker.com ---
Q.1 (a) Explain direct axis and quadrature axis synchronous reactance in synchronous machine. [03]
(b) State important design difference between turbo alternators and hydro generators. [04]
(c) What do you mean by specific electric loading and specific magnetic loading applied to electric machines? State the factors on which the choice of these loadings depends. [07]
--- Content provided by FirstRanker.com ---
Q.2 (a) Explain harmonic induction and harmonic synchronous torques produced in induction motor. [03]
(b) Explain the terms “critical speed” and “run away speed” with reference to synchronous machine. [04]
(c) Explain the term SCR and its effects on synchronous machine performance [07]
OR
(c) Explain steps for design of field winding of synchronous machine. [07]
--- Content provided by FirstRanker.com ---
Q.3 (a) What are the design criteria that should be taken care while design of submersible motors? [04]
(b) Explain which combinations of number of stator and rotor slots should be avoided in the induction motor design? why? [07]
Q.4 (a) Write a note on computer aided design of Induction motor. Explain algorithm steps to find main dimensions. [03]
(b) OR
What is done to reduce tooth pulsation losses in an induction motor? [04]
--- Content provided by FirstRanker.com ---
(c) Discuss the Finite Element Method for design of electrical machine [07]Q.4 (a) Why closed types slots are often used for small induction motors? [03]
(b) In single phase induction explain design of auxiliary winding for capacitor start motor. [04]
(c) What is Dispersion coefficient? Explain the effect of Dispersion coefficient on maximum output power factor. [07]
Q.5 (a) State the rules for the selection of rotor slots. Describe the methods for reducing the effect of harmonics torque. [03]
--- Content provided by FirstRanker.com ---
(b) Explain estimation of full load field mmf in synchronous machine. [04](c) Draw and explain briefly the current distribution wave form speeded over one pole pitch in bars and end rings squirrel cage induction motor [07]
Estimate the main dimensions, air gap length, no of stator slots, stator turns per phase and cross sectional area of stator conductors for a 3 phase, 20 h.p., 400V, 6 poles, 50 Hz, 970 rpm, induction motor, suitable for a star delta starting. Assume magnetic and electric specific loadings as 0.45 wb/m?, and 23000 ac/m respectively, current density = 4 A/mm?, ratio of core length to pole pitch is 0.85, full load efficiency 0.88 and power factor 0.89. [07]
Q.5 (a) Explain how length of air gap is estimated in synchronous machine. [03]
(b) Explain how mmf is calculated for magnetic circuit in synchronous machine. [04]
--- Content provided by FirstRanker.com ---
(c) Determine the main dimensions of a 12 MVA, 13.8KV, 50Hz, 1500 rpm, 3 star connected synchronous generator. The additional data is given as: Bav= 0.6wb/m?, ac=42000 ac/m and peripheral speed= 80m/sec. Find also the maximum flux, the number of stator slots if one conductor per slot is used, and the number of turns per phase. [07]OR
(a) Discuss the effect of “skewing” on the performance of three phase induction motor. [03]
(b) Explain design considerations to eliminate harmonics in synchronous machines. [04]
(c) Briefly discuss factors affecting determining air gap length in induction motor design. [07]
--- Content provided by FirstRanker.com ---
Date: 29/11/2018
Total Marks: 70
--- Content provided by FirstRanker.com ---
This download link is referred from the post: GTU BE/B.Tech 2018 Winter Question Papers || Gujarat Technological University