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Q6. a) Describe a simple single-phase transformer. (6)

b) A 15 KVA, 440 / 110- volt, 50 Hz cycle/sec, single-phase transformer has primary and secondary resistance of 0.12 ohm and 0.0077 ohm respectively. The iron loss of the transformer is 0.16 kW. Calculate the efficiency of the transformer (10)

i) On full load unity power factor

ii) on 80 per cent full load at a power factor of 0.9 lagging

Q6. (a) Describe the basic principles of a self-excited generator (6)

(b) The armature resistance of a 200 V, shunt motor is 0.4 ohms and the no-load armature current is 2A. When fully loaded and taking an armature current of 50 A, the speed is 1200 rev/min. Find the no-load speed and state the assumption made in the calculation (10)

Q6. (a) Explain in brief the term 'bulwark" and 'freeing port'. (6)

(b) A ballast tank is 15 m long, 12 m wide and 1.4m deep and is filled with fresh water. Calculate the load on the top and short side, if: (10)

(i) The tank is just completely full

(ii) There is a head of 7m of water above the tank top.

Q5. a) List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque? (6)
b) The low-voltage release of an a.c. motor-starter consists of a solenoid into which an iron plunger is drawn against a spring. The resistance of the solenoid is 35 ohm. When connected to a 220 V, 50 Hz, a.c. supply the current taken is at first 2 A, and when the plunger is drawn into the “full-in” position the current falls to 0.7 A. Calculate the inductance of the solenoid for both positions of the plunger, and the maximum value of flux-linkages in weber-turns for the “full-in” position of the plunger. (10)

Q9. A. List the factors that determine the maximum developed torque of the induction motor. (6)

B. The primary and secondary windings of a 500 KVA transformer have resistance of 0.42 Ω and 0.0019 Ω respectively. The primary and secondary voltages are 11000 V and 415 V respectively and the core loss is 2.9 kW, assuming the power factor of the load to be 0.8. Calculate the efficiency on (i) Full load (ii) Half load. (10)

Q4.a) Explain what is meant by the terms wave form, frequency, and average value. (6)

b) A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across 110 V sinusoidal a.c. supply. The circuit has a resistance of 50Ω to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate

(i) The reading on the ammeters

(ii) The form and peak factors of the current wave (10)

Q5. a) Explain the applications of PN junction diode (6)

b) In a full wave rectifier without filter, the load resistance is 4 k Ω. Each diode has a forward resistance of 0.8 k Ω. If the peak voltage applied to each diode is 120 V at 50Hz, calculate:

(i) The average value of current.

(ii) Efficiency and

(iii) Regulation at a load current of 10mA (10)

Q8. A. Sketch an arrangement showing the principal of proportional plus integral (P+I) control loop.

B. Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates.

Q7. A. Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain.

B. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.

Q8. An AC Voltage Of 24 V is connected in series with the silicon diode and load resistance 500 Ohm having forward resistance 1O Ohms. Calculate the peak output voltage.

Q6. A. A series circuit having resistance, Inductance and capacitance is to be operated on a constant voltage supply of available frequency. Indicate graphically how changes will take place in the terms, Reactive terms, i.e. Capacitive reactance and inductance reactance; B. A resistance of 130 ? and a capacitor of 30µF are connected in parallel across a 230 Volt, 50Hz supply. Find the current in each component, total current, phase angle and the power consumed.

Q6. A. What is Prismatic Co-efficient (C_P). Derive the formula C_P = C_b/C_m , where  C_b= Co-efficient of fineness and C_m = midship section area co-efficient.

B. The length of a ship is 18 times the draught. while the breadth is 2.1 times the draught. At the load water plane, the water plane area co-efficient is 0.83 and the difference between the TPC in sea water and the TPC in fresh water is 0.7. Determine the length of the ship and the TPC in fresh water.