Electrical Machine Design 2018 Question Paper — Government College of…
The 2018 Electrical Machine Design previous year question paper (Government College of Engineering and Technology, Jammu), with every question and its marks.
- University: Government College of Engineering and Technology, Jammu
- Subject: Electrical Machine Design
- Course: Electrical Machine Design
- Branch: ELECTRICAL ENGG.
- Year: 2018
- Paper: end-term
- Duration: 180 minutes
- Total marks: 100
Instructions
- Attempt five questions in all, selecting at least two questions from each section.
- Assume missing data, if any.
Questions
Section A
Select at least two questions from each section.
- Q1(a). What are the major considerations in the design of Electrical machines ? [10 marks]
- Q1(b). On what factors do the choice of average flux density in air gap and choice of ampere conductors per meter depend ? [10 marks]
- Q2. Write short notes on : (a) Temperature rise in Electrical Machines (b) Rating of Machines. [20 marks]
- Q3(a). Optimize the transformer design from minimum cost and minimum loss points of view. [10 marks]
- Q3(b). Calculate the kVA output of a single phase transformer from the following data : $$\frac{\text{Core height}}{\text{Distance between core centres}} = 2.8$$ $$\frac{\text{Diameter of circumscribing circle}}{\text{Distance between core centres}} = 0.56$$ $$\frac{\text{Net iron area}}{\text{Area of circumscribing circle}} = 0.7$$ Current density = $2.3 \text{ A/mm}^2$, frequency = $50 \text{ Hz}$, window space factor = $0.27$, flux density of core = $1.2 \text{ Wb/m}^2$, distance between core centres = $0.4 \text{ m}$. [10 marks]
- Q4(a). Discuss different methods of Cooling Transformer. [10 marks]
- Q4(b). Determine the main dimensions of the core, the number of turn and cross-section of conductors for a 5 kVA, 11000/400 V, 50 Hz, single phase core type distribution transformer. The net conductor area in the window is 0.6 times, the net cross-section iron in the core. Assume a square cross section for the core, flux density $1 \text{ Wb/m}^2$, a current density $1.4 \text{ A/mm}^2$, and a window space factor 0.2. The height of window is 3 times its width. [10 marks]
Section B
Select at least two questions from each section.
- Q5(a). A 15 kW, 3 Phase, 6 Pole, 50 Hz, squirrel cage induction motor has the following data : Stator bore diameter = $0.32 \text{ m}$; axial length of stator core = $0.125 \text{ m}$; number of stator slots = $54$; number of conductors per stator slots = $24$; current in each stator conductor = $17.5 \text{ Amp}$; full load power factor = $0.85$ lagging. Design a suitable Cage Rotor giving number of rotor slots, section of each bar and section of each ring. The full load speed is to be about $950 \text{ r.p.m}$ approximately. Use copper for the rotor bars and rings. Resistivity of ring is $0.02 \text{ ohms/m} \text{ }\&\text{ } \text{mm}^2$. [12 marks]
- Q5(b). Discuss the factors on which the length of air gap depends. [8 marks]
- Q6(a). A 15 kW, 440 V, 4 Pole, 50 Hz, 3 Phase induction motor is built with a stator bore $0.25 \text{ m}$ and a core length of $0.16 \text{ m}$. The specific electrical loading is $23000 \text{ ampere conductors per metre}$. Using this data of machine, determine the core dimensions, number of stator slots and number of stator conductors for a $11 \text{ kW}$ $460 \text{ V}$, $6 \text{ pole}$, $50 \text{ Hz}$ motor. Assume a full load efficiency of $84 \text{ percent}$ and a power factor of $0.82$ for each machine. The winding factor is $0.955$. [12 marks]
- Q6(b). Explain the term SCR and its effects on the machine performance. [8 marks]
- Q7(a). Find the main dimensions of a 100 MVA, 11 kV, 50 Hz, 150 r.p.m. 3 phase water wheel generator. The average gap density is $0.65 \text{ Wb/m}^2$ and ampere conductors per metre are $40,000$. The peripheral speed should not exceed $65 \text{ m/s}$ at normal running speed in order to limit the runaway peripheral speed. [10 marks]
- Q7(b). Explain the design of damper winding. [10 marks]
- Q8(a). Determine the main dimensions, turns per phase, no. of slots, conductor cross-section and slot area of a 250 h.p, 3 phase, 50 Hz, 400 volt, 1410 r.p.m slip ring induction motor. Assume $\text{B}_{\text{av}} = 0.5 \text{ Wb/m}^2$, $\text{ac} = 30000 \text{ A/m}$, efficiency = $0.9$ and power factor = $0.9$, winding factor = $0.955$, current density = $3.5 \text{ A/mm}^2$. The slot space factor is 0.4 and the ratio of core length to pole pitch is 1.2. The machine is delta connected. [10 marks]
- Q8(b). What are the limitations of traditional designs ? Why do we need CAD analysis ? [10 marks]