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Transcript
78ET-2
Sr. No. 4
EXAMINATION OF MARINE ENGINEER OFFICER
ELECTRO TECHNOLOGY
CLASS II
(Time allowed - 3 hours)
Total Marks 100
INDIA
N.B. -
Morning Paper
(1) Attempt SIX questions only with minimum of ONE question from each part.
(2) All questions carry equal marks.
(3) Neatness in handwriting and clarity in expression carries weightage
Section A
1. The arms of a Wheat-stone bridge have the following resistance : AB = 10 , BC = 20 , CD = 30 , DA = 10 .
A galvanometer of 40  resistance is connected across BD. Calculate the Potential Difference
maintained across AC to cause a current of 3.08 mA (milliamperes) to flow from D to B.
2. A battery is formed of ten cells joined in series. When the external resistance is 8  the current is 1.5
Amperes and when it is 18 , the current falls to 0.75 Amperes. Find the e.m.f. of each cell and its
internal resistance.
3. A shunt generator supplies 100 amperes at a terminal voltage of 100 volts. The prime mover is
developing 23.8 K.W. Shunt field resistance 50 ohms and armature resistance 0.1ohms. Find (a) the
copper losses, (b) the iron and friction losses. (c) the commercial efficiency.
4. A single-phase transformer with a ratio of 440/200V takes a no-load current of 8A at a power factor
of 0.25 (lagging). If, the secondary supplies a current of 220A at a power factor of 0.8 (lagging),
estimate the current taken by the primary from the supply.
5. If the a.c. resistance of each diode section of a thermionic full-wave rectifier is 400 and the circuit
provides a d.c. output of 250V at 50mA, calculate the turns ratio of the power transformer required.
The input a.c. voltage is 240V at 50Hz.
6. In a certain triode, the anode current is 5mA with an anode potential of 220V and a grid potential of
-3V. When the anode potential is increased to 260V, the current rises to 7mA and a change of grid
potential to - 4V restores the current to its original value. Determine the valve constants.
Section B
7. (a) Explain the meaning of each of the following with reference to fuses:
(i) Discrimination. (ii) Fuse rating (iii) Fusing factor.
(b) State with rearons, which class of fuse you would expect to find in the following circuits:
(i) Electric pump motor. (ii) Electro-hydraulic steering gear motor.
8. (a) State the conditions which must be satisfied before an a.c. generator can be paralleled with live
bus-bars.
(b)After an a.c. generator has been paralleled explain how the following are achieved for the
incoming generator:
(i) Correct kW load sharing.,
(ii) Correct load current when the generator has a different power factor to the other generators.
9. (a) With reference to single phasing applied to a.c. motors:
(i) Explain the meaning of single phasing; (ii) Describe its effect,
(iii)State the most common cause of single phasing.
(b)Sketch a simple diagram of a direct on line starter,showing in detail the overload and single phase
protection trip.