MET-OCT-2020

Q1. Differentiate between squirrel cage and wound rotor motor of the three phases: a.c. induction. In respect of the following; A. Rotor construction, B. Torque characteristic, C. Speed variation.

Q2. What is the meant by "excitation" in an alternator? With the help of a neat diagram of brushless alternator labeling all the important parts. explain how the excitation is achieved in a brushless alternator.

Q3. Explain why it is necessary to have reverse power protection for alternators intended for Operation. A. Sketch a reverse power trip; B. Explain briefly the principle on which the operation of this power trip is based and How tripping is activated.

Q4. A. Sketch a standby battery charging/discharging circuit; B. Describe the circuit sketched, making special reference to how battery charge is maintained and how it operates upon loss of main power.

Q5. With reference to an emergency source of electrical power in cargo ships: - A. Describe a typical power source. B. Give a typical list of essential services, which must be supplied simultaneously; C. Explain how the emergency installation can be periodically tested.

Q6. A. With the aid of delta and star connection diagrams, state the basic equation from which delta – star – delta conversion equation can be derived.

B. Three batteries A, B and C have their negative terminals connected together, between the positive terminals of A and B there is a resistor of 0.5 ohm and between B and C three is a resistor of 0.3 ohm
i. Battery A 105 V, Internal resistance 0.25 ohm
ii. Battery B 100 V, Internal resistance 0.2 ohm
iii. Battery C 95 V, Internal resistance 0.25 ohm
C. Determine the current values in the two resistors and the power dissipated by them.

 

Q7. A. Explain the potential hazards of liquid-cooled transformers are used onboard ships.

B. What are the losses in transformers? Mention the various factors which affect these losses.

In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. Losses are respectively 350 and 400 watts. Calculate the efficiency at half-full load, 0.8 power factor.
 

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.

Q9. 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. A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the KVA rating of the other alternator and the power factor.