B.TECH - Semester 3 electrical machines i Question Paper 2020 (feb)
Practice authentic previous year university questions for better exam preparation.
Sample Questions
- Derive the emf equation of dc generator.
- What is armature reaction?
- An 8 pole lap connected armature has 40 slots with 12 conductors per slot generates a voltage of 500 V . Determine the speed at which it is running if the flux per pole is 50 mWb .
- What is back emf?
- Why are starters required in dc motors?
- Draw the vector diagram of a single phase transformer under no load condition and explain the quantities involved. P.T.O.
- What do you mean by oscillating neutral?
- What are the losses in a single phase transformer?
- What is all day efficiency?
- Draw the torque speed characteristics of a dc series motor. > PART - B > Module - 1
- (a) Explain the constructional details of a dc generator with neat sketch. 10
- (b) A short shunt compound generator delivers 100 A to a load at 250 V . The generator has shunt field, series field and armature resistance of $130 \Omega$, $0.1 \Omega$ and $0.1 \Omega$ respectively. Calculate the voltage generated in armature wind...
- (a) Explain the process of voltage build up in a self excited dc generator. 10
- (b) Explain the process of commutation in dc machine and describe the methods to improve it. 10 Module - 2
- (a) Explain the different methods of speed control of dc motors. 10
- (b) Describe Swinburne's test with the help of a neat diagram. What are the main advantages and disadvantages of this test? 10
- (a) Explain the power flow in a dc motor. 10
- (b) A 200 V shunt motor develops an output of 17.158 kW when taking 20.2 kW . The field resistance is $50 \Omega$ and armature resistance $0.06 \Omega$. What is the efficiency and power input when the output is 7.46 kW ? 10
- (a) Derive an expression for induced emf of a transformer.
- (b) A 40 kVA , single phase transformer has iron losses of 800 W and copper loss of 1140 W when supplying its full load at unity power factor. Calculate the efficiency of the transformer at unity power factor at full load and half load.
- (a) Explain the phenomena of harmonics in three phase transformers.
- (b) Explain Sumpner's test for finding efficiency of a single phase transformer and what is its advantage?