oral preparatory for electrical
- Enumerate the difference between primary & secondary cell?
- Enumerate the difference between lead-acid & nickel cadmium cell?
- Describe construction & working of lead acid cell.
- Describe construction & working of nickel – cadmium cell.
- Describe maintenance free battery?
- How is battery charging done?
- How will you measure the state of charge of the battery in (i) Lead acid cell (Ans. Use hydrometer) (ii) NI-cd cell (Ans. Use voltmeter)
- How does the hydrometer work?
- What checks do you do in a battery room?
- Where is the battery room located? What precautions are taken in the battery room?
- Draw a sketch & name the devices taking power from the emergency switchboard (E.S.B)? What safeties are there on E.S.B)?
- What is single phasing? What will happen to the fall. If single phasing occurs: (i) When a motor is stationary (ii) When a motor is running?
- Describe the construction & working of a megger? Where do we use it? What is the least acceptable value of insulation resistance? When is the best time to take insulation resistance?
- What is KVA? What is special about Steering gear Overload safety?
- Explain the condition for Paralleling of Alternators?
- What does different position of the synchroscope needle mean; what is the difference between 6 o clock and 12 clock?
- Why do we close the switch at 11 o'clock and not at 12 o' clock?
- Why is a Megger used for insulation test and not a multi meter?
- What are the safeties on MSB?
- When does Reverse power flow?
- What is the harm if reverse power flows?
- How is the protection against reverse power given?
- How do you test reverse power trip?
- What is the full form of ACB?
- 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 purpose of the earth fault indication on the switch board?
- If you get an earth fault alarm what will you do?
- What is Direct Current?
- What is alternating current?
- What is meant by phase in AC?
- Is there phase in DC?
- Why is DC not much in use now?
- Where are you likely to see it used?
- What does three-phase current mean?
- What is rms value?
- What is the meaning of power factor?
- What is the usual value you see onboard?
- What is the best value possible?
- What is the benefit of improving power factor?
- How can it be improved?
- What is the meaning of saying I and V are in phase?
- What is the difference between KW, KVA and KVAR?
- Why are motor ratings given in KW and that of alternator and transformer given in KVA?
- Where does reactive power go?
- What is a semi conductor?
- What is doping?
- What happens to insulation when temperature rises?
- What happens to resistance of conductors when temperature rises?
- What is an induction motor?
- What is "slip"?
- What is a synchronous motor?
- Where is it used?
- How do you use a multimeter?
- What is an AVO meter?
- How do you check continuity?
- What limits the electrical load?
- What is the voltage used in a meggar?
- How does current flow during welding?
- What do we use for welding on ships? AC or DC?
- What is the voltage?
- What is the voltage used for ignition in boilers/incinerators etc.?
- Why is it different from that for welding?
- Does current flow through hull during welding? If so why don't you get a shock?
- What is safe voltage to prevent shock?
- What is the meaning of earthing in a ship?
- What is the meaning of Star winding/ Delta winding?
- Is the ship's alternator Star wound or Delta wound?
- What is the meaning of ACB, MCCB, NFB?
- What is a magnetic contactor? Where is it used?
- 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 meaning of short circuit?
- How is protection provided for OL and SC?
- What is the function of a fuse?
- What is the normal setting of overload relays?
- How does a thermal overload relay work?
- What is single phasing? How can it happen?
- What is the harm caused by this?
- What protection is provided against this?
- Why is it necessary that incoming alternator frequency is more than bus bar?
- What is dark lamp and bright lamp method for synchronizing? How is the connection made?
- Apart from renewing bearings is there any reason for opening up motors for maintenance?
- Why is reverse power protection required?
- Why is this reverse power used instead of reverse current in alternators?
- What is the meaning of excitation in an alternator?
- Is the field current in an alternator AC or DC ?
- Is the field rotating or stationary? How is it supplied?
- What is a brush less alternator?
- How is the excitation achieved in this?
- What is the meaning of residual magnetism?
- Why is an air compressor started unloaded?
- How is the speed of a 3-phase induction motor varied?
- How is the direction of rotation varied?
- How does this cause a rotation to change?
- How is the speed of a DC motor varied?
- How is the direction varied?
- What is a diode?
- What is a zener diode?
- What is a thyristor? What is an SCR?
- How does an inverter work?
- How does a tube light work?
- What is the function of the starter in a tube light?
- What is the function of the choke?
- Where is a slip ring used and where is a commutator used?
- What is capacitance?
- Does current flow though a capacitor?
- What is the unit for capacitance?
- What is a neutral?
- What is the difference between neutral and earth?
- What is a synchronous condenser?
- Where and why is it used?
- If a motor is wound star and you want to change to delta what should you do?
- If 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?
- Sometimes, when you change the running direction of a E/R blower (from supply to exhaust) it trips. Why?
- What is the function of the friction clutch mechanism used in purifiers?
- What is the regular maintenance done on batteries?
- What safety precautions need to be taken during maintenance on batteries?
- Why is special lighting used in battery rooms?
- What is the voltage available from each cell in a lead acid battery?
- What is the full battery voltage?
- How is this voltage achieved?
- What is the meaning of a normally open contact?
- How does a Salinometer function?
- How does the air compressor start and stop automatically?
- How is the cold room temperature maintained?
- What is a self-monitoring alarm circuit?
- Out at sea, if there is a black out during your watch, what action will you 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?
- If all your air bottles are at low pressure and there is a blackout how do you start the generators?
- What is a shaft generator?
- Even though the main engine runs at varying speeds, how does the alternator maintain constant frequency?
- Is the alternator connected star or delta?
- Why is 440 V used for motors and 110/220 V used for lighting?
- What’s a multimeter? Where & how do you use it?
- How do you measure the resistance of a conductor like say a wire?
- What will happen to the resistance of fall when temp is increased (i) Conductor (ii) Insulator (iii) Semi-conductor.
- Explain how earth fault lamps work?
- What is insulated neutral & earthed neutral distribution?
- What safeties exist in pump or compressors or other motors & starter?
- What safeties exist in steering gear motor? Why is not overload trip fitted?
- What will you do if the motor (steering gear) overload alarm if heard?
- Describe the construction & working of all types of starters?
- How will you measure the insulation resistance of M.S.B without opening it? (Ans. Use M.S.B. insulation resistance meter)
- How will you increase insulation resistance of a motor without opening? (Ans. Use space heater or halogen lamps)
- What is meant by leasing & lagging p.f (i.e power factor)?
- Why is power factor usually 0.8 lagging on a ship?
- What are the effects of low p.f?
- What p.f correction equipment can be used? Why is such a device not used on board (Ans. All loads on a ship are pre-determined)
- What types of bearings does a motor have & why?
- Give examples of reversible motors used on board (Ans. E/R blower, windless / winch motor? How are they made reversible? (Ans. They have 2 sets of winding & a contactor which will engage & disengage with C.W or C.C.W rotation alarm)
- How do you define current, voltage, true power, apparent power, reactive power phase, phase difference phase sequence etc?
- Describe the working principle of A.C. generators, D.C. generators. A.C motors (induction & synchronous) D.C. motors & transformers?
- What are the similarities & difference between A.C & D.C. generator?
- Can you run a 1-Ф motor on 3-Ф supply & vice-versa ? If so, how?
- Is there any difference between D.C. Motor & D.C generator?
- What are the reasons for failure of a D.C generator & A.C. generator to build up voltage?
- What will happen if you connect an A.C motor to D.C. Supply?
- What will happen if you connect an d.c motor to A.C. supply
- What is a universal motor?
- How will you reverse the direction of rotation of foll: (i) synchronous motor (ii) 3- Ф induction motor (iii) 1- Ф induction motor (iv) d.c. Motor
- What could be the causes of failure to start in case of above motors
- How will you top up the electrolyte in a lead acid battery? Will you mix acid in H2O or H2O in acid?
- Why are coupling bolt bushes used the coupling between motor & driven machine?
- What’s the difference between star & delta connection? Why are alternators usually connected in star?
- The 440V that is shown on voltmeter is voltage between single phases or across 2-phases? Is it maximum value?
- What meters are there on M.S.B? (Ans. Voltmeter, ammeter, frequency meter, KW meter, insulation, resistance meter)
- What gases are released in the battery room & what are the usual safety provisions given?
- Why is only distilled water used?
- What is remedial action is taken if it falls on the skin?
- Describe the principle of operation, charging & discharging of a lead acid battery?
- Sketch an emergency battery charging arrangement that can be charged by A.C. mains. Show the trickle charge & quick charge with a change over arrangement. How is this charge maintained? How do you test the system?
- Explain how each of the following Component defects are repaired: - a) Burnet insulation at the terminals of an A.C. motor b) Badly grooved commutator on A.C. starter. C) Badly grooved commutator on D.C. machine. D) Winding of an A.C stator severely dampened by water. E) Motor windings overheated due to excessive greasing of bearings.
- How do you convert 3- Ф to 6- Ф supply?