Category: Electrical

Q1. What is KVA?KW is the unit of real power and kVA is the unit of apparent power. Apparent power = Real power + Reactive power. kW = kVA x p.Q2. Explain the condition for Paralleling of Alternators? Phase, Phase sequence, Voltage, Frequency.Q3. Why is Megger used for insulation test and not a Multi meter?Multimeter uses a DC source battery for measuring resistance. For very high resistances voltage must be high for current to flow. Thus a megger with DC gen is used.Q4. What is the harm if reverse power flows? Damage to prime mover, other generator overloaded, undesirable condition. Q5. What is the purpose of the earth fault indication on the switch board? To indicate earth fault leakage current. Q6. If you get an earth fault alarm what will you do? Accept alarm. Fault finding by isolating circuits. Q7. What is the direct current? Unidirectional flow of current.Q8. Why DC not much in use now? Easy production, transmission of AC. Size of equipment, losses. Q9. Where are you likely to see it used? Battery charging circuits, control circuit.Q10. What is the meaning of power factor? Ratio of real power to apparent power. Q11. What is the usual value you see onboard? 0.85 to 0.92 Q12. What is the best value possible? As close as possible to unity Q13. What is the benefit of improving power factor? Reduction in losses due to reactive power. Q14. How can it be improved? Use of capacitors and synchronous motors.Q15. What is the difference between KW, KVA and KVAR?Kilo Watt - Actual power load dependent. Power, power supplied to do work. Kvar- unit of reactive power. KVA = KVAR + KWQ16. What is a doping? Adding impurities to semiconductors to improve conductivityQ17. What is an induction motor? Motor in which current supplied to stator induces a current in the rotor. Faraday’s law of electromagnetic induction.Q18. What is “Slip”? difference between speed of rotation of magnetic field and speed of rotor. Slip is load dependent.Motor where both stator and rotor are supplied with current. Slip is zero. Q19. Where is it used? Pump and fan drives, main propulsion and improvement of power factorQ20. How do you check continuity? MultimeterQ21. What is the voltage used in a meggar’? 500v DCQ22. What do we use for welding on ships? AC or DC? AC Q23. Why is it different from that for welding? Welding high current, ignitor high voltage. Q24. Is the ship’s alternator Star wound or Delta wound? Star because it has a strong neutral point. Q25. What is a magnetic contactor’? Where is it used? Magnetic contactors are those which open or close depending upon position of spring by magnetic force of a current carrying coil. Relays, trip circuits,starters.Q26. How is protection provided for OL and SC? OL-Electromagnetic trips, thermistors, bimetallic strips.Q27. What is the function of a fuse? Protection against over current, isolate circuits for maintenance, rapid clearance for s/c faultsQ28. How does a thermal overload relay work? Bimetallic strips with different co efficient of thermal expansionQ29. What is a single phasing? Loss of current through one phase in a 3 phase supply. 2.4 times line current and 1.3 times current in each windingQ30. How can it happen? Broken terminals, broken wires, fuse blown, relay not making contact, spring damaged, oxidation products on contactorsQ31. What protection is provided against this? Same as overload trips. Q32. Why is it necessary that incoming alternator frequency is more than bus bar? For proper synchronizationQ33. Why is reverse power protection required? To avoid motoring effect. Q34. Why is this reverse power used instead of reverse current in alternators? Reversal of current flow cannot be detected in AC supply. Q35. What is the meaning of excitation in an alternator? Dc supply to rotor of alternator for producing magnetic field. Q36. Is the field current in an alternator AC or DC? DC Q37. Is the field rotating or stationary? RotatingQ38. What is the meaning of residual magnetism? Magnetism remaining in the core of the electromagnet after removal of coil current. Q39. Why is an air compressor started unloaded? Reduce starting current of the motor Q40. How is the speed of a 3-phase induction motor varied’? resistance control and pole change rotor. Q41. How is the direction of rotation varied? Changing terminal connections Q42. How does this cause a rotation to change? Reversal of direction of rotating magnetic field. Q43. How is the speed of a DC motor varied’? field control, armature control- thyristor control and ward leonard system. Ac motor- dc generator- DC motor. Q44. How is the direction varied? By varying the field current of the DC generator by use of potentiometer. Q45. What is a diode? Single junction semiconductor device. Q46. What is a zener diode? Diode designed to operate in reverse bias direction with a small breakdown voltage. Q47. What is a thyristor? What is an SCR? Thyristors are solid state switching devices triggered by gate electrode. SCR are four layer semiconductor devices Q48. How does an inverter work? 12V DC fed to Oscillator circuit- Aplifier – Primary of transformer –Secondary… Q49. What is the function of the starter in a tube light’? provide initial path of current flow through both cathodes of tube during starting Q50. What is the function of the choke? Provide high starting voltage for ionization of gas and subsequently control voltage to maintain ionization. Q51. Where is a slip ring used and where is a commutator used? Commutators used in DC gen to draw current. Slip rings used to supply current to rotor of AC Alternator. Slip Ring + Brushes, Commutator +Split Rings Q52.What is capacitance? Ability of a body to store charge in an electric field. Q53.Does current flow though a capacitor? No Q54.What is the unit for capacitance? Farad. 1 Farad = 1 Coulomb / 1 volt Q55. What is a neutral? Common point of star connection where sum of currents is 0 Q56.What is the difference between neutral and earth? Earth is a connection for passage of leakage current to the ground. In some cases the neutral point is earthed to detect any leakage. Q57.What is a synchronous condenser? similar to synchronous motor but it does not drive anything. Q58.Where and why is it used? Used in electrical circuits to improve power factor by increasing or decreasing power factor. Used to generate or absorb reactive power as required to improve power factor by increasing or decreasing field excitation. Q59.Sometimes, when you change the running direction a ER blower (from supply to exhaust) it trip, Why? Over current trip. Q60.What is the functions of the friction clutch mechanism used in purifiers? Reduce starting current of purifier motor. Q61.What is the regular maintenance done on batteries? All vents clear, measure sp. Gravity, level of electrolyte, Vaseline on contacts, boost charging, all connections tight and corrosion free. Q62.What safety precautions need to be taken during maintenance on batteries? Avoid sparks by falling tools, remove leads on batteries. Insulate leads, avoid touching to floor, non metallic jugs to be used, instruments used to be intrinsically safe. Q63.How is this voltage achieved? By using cells connected in series. Q64.What is the meaning of normally open contact? Contacter open under normal operating cond. Q65.How does a Salinometer function? Measuring flow of current through a known quantity of water. Q66.How does the air compressor start and stop automatically? Pressure switches in air bottle. Q67.How is the cold room temperature maintained? Q68.What is a self-monitoring alarm circuit? Alarm circuit which is activated due to any abnormality in working conditions or abnormality in alarm system. eg OMDQ69. If all your air bottles are at low pressure and there is a blackout how do you start the generators? Start emg air comp and fill emg air bottle. Q70.What is a shaft generator? Driven by ME to supply power . Q71.Even though the main engine runs at varying speeds, how does the alternator maintain constant frequency? Frequency converter.Q72. What type of starters are used on board and why? DOL Star Delta Q73. What is the difference between current and voltage? Voltage is the force which cause s the flow of charge and rate of flow of charge is currentQ74. What services and machinery are supplied from the emergency switchboard? Emergengy lighting,navigaton lights, VHF radio, internal comm., nav equipment, fire detc n alarm day light signaling, whistle,call points, internal signals, fire pump, steering gear, emergency bilge pump, one sea water pump, DO supply pump, water tight doors, sprinkler pump, emergency fire pump.Q75. What actions will you take if Motor gets hot during your watch? Stop, check bearing, alignment, insulation resistance, single phasingQ76. How are emergency batteries maintained? charging circuitQ77. State safeties on a Motor circuit. Overload protection – thermistors, by metallic strips, electromagneticQ78. Battery room safety. Construction – prevent spilling, emission of spray, accessible from top and one side, crates and trays of non absorbent insulation material, deck below acid/alkaline resistant. No smoking and no naked lights, approved elec apparatus, location on deck, forced air circulation, no tube lights, non metallic jugs, separation of vent duct from other ducts, explosion proof lighting, proper wattage, sealing of enrty of cables, fittings not painted, loose wires and tools not to be kept on the batteris, tools spark proof and insulated. Q79. Requirement of starting of emergency generator. 45 secs Q80. Working principle of high temp of jacket cooling water. Thermocouple/ bimetallic strip Q81. Electrical motor overheat, reasons. Single phasing, over load, short circuit, bearings burnt out, air gap, obstruction in rotation. Q82. Principles of earth fault, reasons. .Break down of IR Q83. Maintenance of electrical switchboard. Fans, silica gel packets, indicating lamps, earth fault, MSB lamps,Q90. Checking alarm of navigation lights. Removing contacts. Q91. How to check earth fault in navigation lights. Insulation resistanceQ92. Effects if earth faults is not rectified. Over load, heating up, leakage current, shock, burning, fire,Q93. Indication of single phasing in case of running motor. Hunting of motor, fluctuation of motor rpm, over load protection will operate, humming noise, heating up of motor, vibration, reduction in torque,Q94. Can motor run on single phasing, and how to check. Yes. Q95. Problems faced in Lambda/Delta starter. Starting torque is reduced. Q96. factors affecting power factor. Inductive and captive loads Q97. Working of SINGLE PHASE motor. In a single phase motor the single phase supply generates opposite polarities which is only alternating but not rotating, so the single phase motor wont turn but will keep on turning once started. Thus an extra starting winding with a capacitor or inductor is used to cause the flux to lead or lag the current in the main field. Q98. Indications of Navigational bulb functioning. Automatic indication which gives audible and visual alarm in case of failure Q99. How to check fuses? Continuity, resistance Q100. Types of fuses. Cartridge/ Semi enclosed (reusable)Q101. Relation between frequency and Speed. Ns = 120f / PQ102. How to improve insulation resistance motor? Keeping in dry location, vent holes clear.Q103. E/R crane electrical safeties. Port/stbd/fwd/aft limit switches. Hoist limit switch, emergency stop, slip clutch, overload, slack wire. Q104. Conductance, resistance [Values, comparison with different materials] conductance is opposite to resistanceQ105. How to check diode? Fwd bias minimum resistance, reverse bias- high resistanceQ106. Starting procedure of synchronous motor. 1. Speeding up rotor to synchronous speed external means, 2. Use of Pony (Induction) motor to speed up. 3. Copper embedded bars on tips of rotor poles, shorted by end plates, started as induction motor, at max speed DC excitation for synchronization.Q106. Pump room bulb replacement. Light and fan interlocked. Isolate circuit, arrangement for ventilation done. Enclosed space entry. Replace. Q107. Checks on motor after rewinding ( and Connection) Insulation resistance, earth fault, air gap, alignment, contactors Q108. What if shore frequency is less? Motors will run slower, stalling, vibration, overheat. Voltage should also vary in the same proportion.Q109. Ohm’s law. Current flowing through a conductor is directly proportion to the potential diff across it and inversly proportional to resistance Questions are given below please answer them in comment box. we will update in the form.What is special about Steering gear Overload safety?Why do we close the switch at 11 o’clock and not at 12 o’clock? What does different position of the synchroscope needle mean,what is the difference between 6 o clock and 12 o clock? What are the safeties on MSB? When does Reverse power flow? How is the protection against reverse power given?How do you test reverse power trip? What is the full form of ACB? Air circuit breaker.If you press the ACB Close button on an idle generator what will happen? What is under-voltage protection? What is the meaning of preferential trip? Why is it provided?What is the alternating current?What is meant by phase in AC? What does three-phase current mean? What is the RMS value? How can it be improved?What is meaning of saying I and V phase?Why are motor rating given in KW and that of alternator and transformer given in KVA?Where does reactive power go? What is a semi conductor?What happens to insulation when temperature rises? What happens to resistance of conductor when temperature rises? How do you use a Multimeter?What is an AVO meter’What limits the electrical load? What is the voltage? What is the voltage used for ignition in boilers/incinerator etc? Does current flow through hull during welding? If so why don’t you get a shock?What is a safe voltage to prevent shock? What is the meaning of earthing in a ship?What is the meaning of star winding? Delta winding?What is a relay? How is it different from a magnetic contactor?Can you draw a DOL starter circuit? What is the meaning of overload?What is the meaning of short circuit? What is the normal setting of overload relays?What is the harm caused by this? What is a dark lamp and bright lamp method for synchronizing? How is the connection made? Apart form renewing bearing is there any reason for opening up motors for maintenanceHow is it supplied?What is a brush less alternator? How is the excitation achieved in this?How does a tube light work?If a motor is wound star and you want to change to delta what should you do?f the AVR, is defective, when additional loads come on will the generator be able to take it?How do you test, reverse power trip, high current trip, preferential trip? What is residual magnetism? Where is it important? Why is special lighting used in battery rooms? Risk of explosion.What is the voltage available from each cell in a lead acid battery? What is the full battery voltage? How is the cold room temperature maintained? Out at sea, if there is a black out during your watch, what action will take? After a black out the emergency generator comes on, On restoring the main supply we are closing the circuit breaker of the main generator with out bothering about synchronizing. How is this possible? How does the emergency generator start automatically?Why is 440 V used for motors and 110/220 V used for lighting?State the electrical and mechanical trips on A/E? Draw a sketch of a Synchroscope? How is load taken on GeneratorsWhile one generator is being connected to a Busbar, both the generators trip, what may be the cause’? How is the generator taken on load in parallel?What are the safeties on a Switchboard, Define preferential trip and reverse power relay?How will you start a generator? How is current generated in a alternator?What is the difference between AC and DC current?How will you convert 440 V AC supply to 24 Volt DC?How rectifiers function?Why emergency generators are fitted on board?What action will you take if Busbar catches fire?What is the phase factor and power factor relation on a Busbar.State safeties provided on ACB’s. Action to be taken for electrical shock.Sketch a circuit diagram of AE panel. State different types of Motor and voltages available on Ships. Calculate the power of induction motor. Define open circuit, short circuit and earth fault. How to check them.Safety of an alternator.Maintenance of alternator. Asynchronous motor. Pump room ventilation and type of lighting.Single phasing protection.Types of motors.Motor fitted on governor. SynchronousSimulation of engine tripsTrying out generator lube oil pressure cut out. Measurement of insulation resistance.Requirement of emergency batteryBattery start engine. Earth fault checking on motor/busbar.Over load trip and how much in generator. Emergency battery generator. Reverse power relay.Types of starters with diagrams. Earthing onboard ship, finding and how it is rectified.Emergency light distribution on board.Explosion proof Installations. Resistance Vs Temperature GRAPH.How to check battery is fully charged, what will you check and maintenance done. Maintenance on batteries.Requirement for emergency batteries.Action taken for steering gear trip. Setting of floating charge and how it worksGenerator engine safeties and how to check.Electrical safeties are set on what parameters. Batteries charging and specific gravity values. Types of motor found on ship.What is squirrel cage motorMaintenance of navigational light. Paralleling of A/E Generator. How to decide capacity of fuses. Effects of single phasing and definition.Sketch and describe megger working.Battery room location, safeties. Power factor , active, reactive.factors affecting power factor. Draw Sine wave. Megger, clamp meter, Insulation resistance, causes of IP. Motor Protection.Loadline regulation, significance.Continuity checking & long wire from E/R to bridge.SCRDOL starter figure. 3 PHASE induction motor, safetiesPrinciples of induction motor.Types of transformer, working principle. Principle of motor.Checks on alternator, if not developing voltage. Single phase protection testing. Zener diode function and use where’? 2 Lamp method (bright and dark) Difference between fuse and trip.Synchronous Vs Induction motor. Advantage and disadvantage of lead acid and alkaline batteries. If Synchrono-scope fails, how to parallel generatorFIRC FuseTrickle charging.Motor direction reversing.How?250.Show with a sketch how emergency generator and main generators are arranged? How does the emergency generator start on failure on main power?

Category: Electrical

ELECTRO TECHNOLOGY AND CONTROL ENGINEERING

MEO CLASS IV ORAL