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Q9. A. Discuss different methods of speed control of a d.c. series motor by adjusting field ampere turns.

B. A 230 V, d.c. shunt motor runs at 1000 r.p.m and takes 5 amperes. The armature resistance of the motor is 0.025𝛀 and shunt field resistance is 230𝛀. Calculate the drop in speed when the motor is loaded and takes the line current of 41 amperes. Neglect armature reaction.

Q8. A. Explain the significance of the root mean square value of an alternating current or voltage wave form; Define the form factor of such a wave form.

B. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging.

1. Calculate the output of second Alternator.

2. Calculate the value of Power factor of second Alternator.

Q8. A. Electric motors contain a stationary member as well as a rotating member. For each of the following machines, identify in which part of the motor three field winding and the armature winding are located: three phase induction motor, three phase synchronous motor, d.c. motor. B.  An 18.65 KW,4-pole,50HZ, 3 phase induction motor has friction and windage losses of 2.5 percent of the output. The full load slip is 4% compute for full load (a) the rotor Cu loss (b) the rotor input (c) the shaft torque (d) the gross electromagnetic torque.

Q8. A current has the following steady values in amperes for equal intervals of time and changing instantaneously from one value to next: - 0,10,20,30,20,10,0,0, -10,-20,-30,-20,-10,0 etc. Calculate I. Average value 2. RMS value, 3. Form factor and peak factor.

Q9. A. What are the factors which determine the synchronous speed of a motor? B. The star-connected rotor of an induction motor has a stand-still reactance of 4.5 ohms/phase and a resistance of 0.5 /phase. The motor has an induced emf of 50 V between the slip-rings at stand-still on open circuit when connected to its normal supply voltage. Find the current in each phase and the power factor at start when the slip-ring is short-circuited.

Q9. (a) Explain the concept of dynamical stability.

(b) A ship of 5000 tonne displacement has three rectangular double bottom tanks A: 12m long and 16m wide; Tank B: 14m long and 15m wide; C 14m long and 16m wide.

calculate the free surface effect for any one tank and state in which order the tanks should be filled when making use of them for stability correction.

Q10. A ship of 15000 tonne displacement has an Admiralty Coefficient, based on shaft power, of 420. The mechanical efficiency of the machinery is 83%, shaft losses 6%, propeller efficiency 65% and QPC 0.71. At a particular speed the thrust power is 2550kW.

Calculate:

(i) Indicated power,

(ii) Effective power,

 (iii) Ship speed.

Q9. With respect to Buoyancy of a vessel:

A. What do you understand by reserve buoyancy what happen if the lost buoyancy is greater than the reserve buoyancy?

B. A forward deep tank 12 m long extends from a longitudinal bulkhead to the ship’s side. The widths of the tank surface measured from the longitudinal bulkhead at regular intervals are 10, 9, 7, 4 and 1 m. Calculate the second moment of area of the tank surface about a longitudinal axis passing through its centroid.

Q4. Just before entering drydock a ship of 5000 tonnes mass floats at draughts of 2.7 m forward and 4.2 m aft. The length between perpendiculars is 150 m and the water has a density of 1025 Kg/m3. Assuming the blocks are horizontal and the hydrostatic data given are constant over the variation in draught involved, find the force on the heel of the sternframe, which is at the after-perpendicular, when the ship is just about to settle on the dock blocks, and the metacentric height at that instant.

Hydrostatic data: KG = 8.5 m, KM = 9.3 m, MCT1 m = 105 MNm. longitudinal Centre of flotation(LCF) = 2.7 m aft of amidships.

Q8. A. Explain the effect of trim on tank soundings. B.A ship of 6600 tonne displacement has KG 3.6m and KM 4.3m. A mass of 50 tonne is now lifted from the quay by one of the ship’s derricks whose head is 18m above the keel. The ship heels to a maximum of 9.5° while the mass is being transferred. Calculate the outreach of the derrick from the ship’s centreline.

Q6. A. Explain the purpose of non-watertight longitudinal subdivision of tanks. B. A ship 90 long displaces 5200 tonne and floats at draughts of 4.95m forward a nd 5.35 m aft when in sea water of 1023 kg/m3. The waterplane area is 1100m2, GML 95m, LCB 0.6m forward of midships and LCF 2.2m aft of midships. Calculate the new draughts when the vessel moves into fresh water of 1002 kg/m3

Q6: A. what is ‘form stability’ & ‘weight stability’. b. A Ship of 5000 tonnes displacement enters a drydock trimmed 0.45m by the stern. KM=7.5m., KG=6.0m. MCTC=120 tonnes-m.  The centre of flotation is 60m. Frome aft. Find the effective metacentric height at the critical instant before the ship takes the blocks overall, assuming that the transverse metacentre rises 0.075m.