DieselShip's Online Content Library

Q5. With reference to three phase induction motors:

a) Explain the phenomenon of crawling and cogging in these motors. (6)

b) The output of an induction motor running at 4% slip is 36.775 kW and the friction and windage losses are 1500W. find the rotor copper loss and motor efficiency if stator losses are 3kW. (10)

Q1. a) Write a short note on the principle of operation of induction motors (8)

b) What is slip for an induction motor? (4)

c) If a 6-pole motor is supplied at 60Hz and runs with a slip of 5%. What is the actual rotor speed? (4)

Q2. Describe how the starting torque of electric induction motors may be improved by using EACH of the following:

(a) Wound rotor; (5)

(b) Double cage. (5)

Q3. a) Write a short note on the principle of operation of induction motors (8)

b) What is slip for an induction motor? (4)

c) If a 4-pole motor is supplied at 60Hz and runs with a slip of 5%. What is the actual rotor speed? (4)

Q2. Explain the methods used to control the speed of a 3 Phase induction motors. Draw and Explain a Variable Frequency Drive used for optimization of energy efficiency of auxiliary machineries on board vessels.

Q3. Explain the matching of an induction electric motor to a pump required for main circulating duty, with the aid of pump characteristic and torque/ship diagrams.

Q4. Explain the effect of reduced voltage on standard squirrel cage motors with respect to EACH of the following:

(i) Burn out; (ii) Starting current; (iii) Starting torque; (iv) Speed.

Q1. a) Explain the term single phasing as applied to poly phase induction motors. (4)

b) State the likely causes of single phasing and the consequences if motors are not adequately protected. (6)

c) Describe with the aid of sketches THREE methods for motor protection should single phasing occur. (6)

Q5. Write short notes on

a) short circuit protection to Induction motors (8)

b) Overload protection to induction motors (8)

Q3. What is soft starting of an Induction Motor? Describe with a circuit using thyristors used for soft starting. Discuss its advantages and disadvantages. (16)

Q3. With reference to squirrel cage, induction, electric motors:

A. Describe the construction of such a motor. (6)

B. Sketch the torque against speed curve of such a motor. (5)

C. Describe a method employed by a retrofitted device used to improve the part load performance of an induction motor. (5)

Q2. a) Briefly explain the principle of Operation of induction Motors (4)

b) What is slip for an induction motor? (4)

c) Draw a simple ladder logic diagram of star delta starting of an induction motor. (8)