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 + KW
Q16. What is a doping?
Adding impurities to semiconductors to improve conductivity
Q17. 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 factor
Q20. How do you check continuity?
Multimeter
Q21. What is the voltage used in a meggar’?
500v DC
Q22. 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 faults
Q28. How does a
thermal overload relay work?
Bimetallic strips with different co efficient of thermal expansion
Q29. 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 winding
Q30. How can it
happen?
Broken terminals, broken wires, fuse blown, relay not making contact, spring
damaged, oxidation products on contactors
Q31. 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 synchronization
Q33. 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?
Rotating
Q38. 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 OMD
Q69. 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 current
Q74. 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 phasing
Q76. How are
emergency batteries maintained?
charging circuit
Q77. State safeties
on a Motor circuit.
Overload protection – thermistors, by metallic strips, electromagnetic
Q78. 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 resistance
Q92. 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 / P
Q102. 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 resistance
Q105. How to check
diode?
Fwd bias minimum resistance, reverse bias- high resistance
Q106. 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 maintenance - How 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
Generators - While 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.
Synchronous - Simulation of engine
trips - Trying out generator
lube oil pressure cut out. - Measurement of
insulation resistance. - Requirement of emergency
battery - Battery 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 works - Generator 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
motor - Maintenance 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. - SCR
- DOL starter figure.
- 3 PHASE induction motor,
safeties - Principles 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 generator - FIRC Fuse
- Trickle 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?