ELECTRICAL MACHINES-I 2018 Question Paper — Government College of Eng…
The 2018 ELECTRICAL MACHINES-I 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 MACHINES-I
- Course: Electrical Machines - 1
- Branch: ELECTRICAL ENGINEERING
- 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.
- Each question carries 20 marks.
- Assume missing data wherever necessary.
Questions
Section-A
- Q1. a) Discuss the influence of highly permeable materials on the magnetic flux lines. (10) b) Explain Biot-Savart Law and also derive its expression. (10) [20 marks]
- Q2. a) Explain the concept of energy and co-energy with suitable diagrams. Derive the expression for energy stored in magnetic field. (12) b) Discuss linear and non-linear magnetic circuits in detail. (08) [20 marks]
- Q3. Explain Armature Reaction in DC Machines in detail. (20) [20 marks]
- Q4. a) Discuss the principle of operation of DC Generator in detail. (10) b) An 8 pole Generator has 500 armature conductors and has a useful flux per pole of $0.065\text{ Wb}$. What will be the emf generated if it is lap connected and runs at $1000\text{ rpm}$? What must be the speed at which it is to be driven to produce the same emf if it is wave wound? (10) [20 marks]
Section -B
- Q5. a) Explain the need of using Starters in DC Machines. Discuss the 3-point Starter in detail and also mention its drawback. (10) b) A $75\text{ kW}$ shunt generator is operated at $230\text{ V}$. The rotational losses are $1810\text{ W}$ and shunt field circuit draws $5.35\text{ A}$. The armature circuit has a resistance of $0.035\text{ }\Omega$ and brush drop is $2.2\text{ V}$. Calculate i) total losses ii) output of prime mover and iii) efficiency at rated load. (10) [20 marks]
- Q6. Explain the various characteristics of DC Shunt and DC Series Motor. (20) [20 marks]
- Q7. Explain Open-circuit and short-circuit tests, polarity test, and back-to-back test of Transformer. (20) [20 marks]
- Q8. a) A $100\text{ KVA}$, $2200/440\text{ V}$ transformer has $R_1 = 0.3\text{ }\Omega$; $X_1 = 1.1\text{ }\Omega$; $R_2 = 0.01\text{ }\Omega$ and $X_2 = 0.035\text{ }\Omega$. Calculate i) the equivalent impedance of the transformer referred to the primary and ii) total copper losses. (10) b) Why are Autotransformers not safe for supplying a low-voltage from high-voltage source? Also Explain the construction and principle of working of Autotransformer. (10) [20 marks]