Q2. Sketch a circuit diagram for an automatic voltage regulator illustrating how the A.V.R. utilizes a Silicon-controlled rectifier to control the excitation system for an alternator.
Describe how the A.V.R. monitors output and controls the excitation system.
Q3. Diesel electric propulsion is now being chosen as the power plant for an increasingly wide variety of vessels.
(a) Sketch a simple layout of such an installation.
(b) Explain the advantages of selecting such a plant.
Q1. In a ship's power system, the neutral on the low voltage side is not grounded, but it is mandatory to ground the neutral in high voltage systems. Discuss in detail for the above difference and with suitable sketches, explain the different earthling arrangements for HV system.
Q2. Describe / troubleshooting the problems in a typical PLC based system taking care of the safety requirements. (Explain each test method according to various steps to be taken in serial order Including setting-up of any instrument to be used)
Q1. Sketch and describe the method of speed control of synchronous motors by variable frequency. State the advantages of this method over the other methods of speed control.
Q6.a) Explain the applications of PN junction diode. (6)
b) A full-wave, 1 -phase rectifier employs a double diode valve, the internal resistance of each element of which may be assumed constant at 500 W. The transformer r.m.s. secondary voltage from the centre-tap to each anode is 300 V and the load has a resistance of 2000 W. Evaluate:- (10)
(i) mean load current.
(ii) r.m.s. value of load current
(iii) the d.c. output power
(iv) the input power to the anode circuit
(v) the rectification efficiency
Q7. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.
b) An 8kw, 230V, 1200 rpm d.c shunt motor has Ra = 0.7W. The field current is adjusted until, on no-load with a supply of 250V, the motor runs at 1250 rpm and draws armature current of 1.6 amps. A load torque is then applied to the motor shaft which causes la to raise to 40 A and the speed falls to 1150 rpm. Determine the reduction in the flux per pole due to the armature reaction.
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 how drooping characteristics cater for stable operation when running in parallel. (6)
b) Two shunt generators X and Y work in parallel. Their external characteristics may be assumed to be a linear over their normal working range the terminal voltage of X falls 265V on no load 230V when delivering 350Ato the busbars, while the voltage of Y falls from 270 V on no load to 240V when delivering 400A to the bus bars. Calculate the current with each machine delivers when they share a common load of 500A. what is thw bus bar voltage under this condition and the power delivered by each machine
Q10. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit. b) An eight – pole alternator running at a speed of 720rev/min supplies current to synchronous and induction motors with forty – eight poles. Calculate the frequency and speed of rotation of the motors if thr induction motor runs with 2 percent slip.
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