JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II ELECTRICAL MACHINES-1 Previous Question Paper (April/May - 2023 - R18)
Note: i) Question paper consists of Part A, Part B.
ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions.
iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Name the different parts of a DC Machine.
Answer
The main parts of a DC machine include the yoke, magnetic poles (pole core and pole shoe), field windings, armature core, armature winding, commutator, brushes, and bearings.
What is the difference between Lap winding and Wave winding?
Answer
In Lap winding, the number of parallel paths is equal to the number of poles (A = P), making it suitable for high-current, low-voltage applications. In Wave winding, there are always only two parallel paths (A = 2), making it suitable for low-current, high-voltage applications.
What are the losses occur in DC Machines?
Answer
Sign in to view the complete answer paper.
What are the applications of d.c. motor?
Answer
Sign in to view the complete answer paper.
What is Field’s test?
Answer
Sign in to view the complete answer paper.
What is the difference between direct and indirect testing of DC Machines?
Answer
Sign in to view the complete answer paper.
What is the transformer ratio?
Answer
Sign in to view the complete answer paper.
Why the transformer rating is in KVA?
Answer
Sign in to view the complete answer paper.
What is the tertiary winding?
Answer
Sign in to view the complete answer paper.
What are the advantages of three phase transformers?
Answer
Sign in to view the complete answer paper.
Part B
What do you understand by demagnetizing and cross magnetizing affects of armature reaction in DC machine?
Answer
Sign in to view the complete answer paper.
A separately excited d.c. generator with constant excitation is connected to a constant resistance circuit. When the speed is 1200 rpm, it delivers 120A at 500V. At what speed will be the current be reduced to 60A? Armature resistance = 0.1 ohm. Contact drop per brush = 1V. Armature reaction may be ignored.
Answer
Sign in to view the complete answer paper.
With the help of neat sketch, Explain how the open circuit characteristics can be obtained and how the critical speed and critical field resistance are determined.
Answer
Sign in to view the complete answer paper.
Describe the principle of operation of DC motor.
Answer
Sign in to view the complete answer paper.
A 120V DC shunt motor has an armature resistance of 0.2Ω and a field resistance of 60Ω. The full load line current and full load speed are 60A and 1800 rpm. If the brush contact drop is 3V. Find the speed of the motor at half load.
Answer
Sign in to view the complete answer paper.
What is the necessity of a starter for DC Motor? Explain in detail about 3– point starter.
Answer
Sign in to view the complete answer paper.
Explain in detail, how the brake test is conducted on DC Shunt motor?
Answer
Sign in to view the complete answer paper.
What are the merits and demerits of Hopkinson’s test?
Answer
Sign in to view the complete answer paper.
With suitable diagram, how the Swinburne’s test can be employed to predetermine the efficiency at full load condition when running as a (a) generator and (b) motor.
Answer
Sign in to view the complete answer paper.
Explain in detail how eddy current and hysterisis losses of a transformer can be minimized.
Answer
Sign in to view the complete answer paper.
At 400 V and 50 Hz the core loss of a transformer was found to be 2400 W. When the transformer is supplied at 200 V and 25 Hz, the core loss is 800 W. Calculate the hysteresis and eddy current loss at 400 V and 50 Hz.
Answer
Sign in to view the complete answer paper.
From the fundamentals, obtain the equivalent circuit of a single phase transformer.
Answer
Sign in to view the complete answer paper.
Derive an expression for the saving of copper in an autotransformer as compared to an equivalent two winding transformer.
Answer
Sign in to view the complete answer paper.
A three phase step down transformer is connected to 6.6 kV supply mains and takes 80A. Calculate its secondary line voltage and line current for the following connections if the ratio of turns per phase is 16. (i) Y-Y (ii) Y-Δ (iii) Δ-Δ.
Answer
Sign in to view the complete answer paper.
Define voltage regulation of a transformer and derive condition for zero and maximum regulation.
Answer
Sign in to view the complete answer paper.
A Scott-connected transformer supplies two single phase furnaces at 100V, each taking 200kW. The load on the leading phase is at unity power factor and that on the other phase is 0.8 lagging power factors. The 3-phase input line voltage is 11000V. Calculate the line currents on the primary side. Neglect the magnetizing current and leakage impedance.
Answer
Sign in to view the complete answer paper.