Marine Electrotechnology
Questions
Answers
1.
10 Mohm
The insulation resistance (IR) to earth of a new galley hot-plate is
measured to be 30 Mohm. When three identical hot-plates are
tested together their combined IR will be:
1.
no fault - hard earth - light earth
The earth lamps in a 3-phase system indicate as follows:
Red= bright Yellow= dark Blue= dim
1.
Prevent manual synchronising outside
permitted limits
1.
Completely loose its share of the load
causing the auxiliary engine to speed up
1.
Reduce motor speed by about 10%
Check-synchroniser equipment is often installed to:
Due to failure of one of the carbon brushes the
excitation voltage is lost on one alternator that is
operating in parallel. Will that alternator then:
A 10% reduction in generator speed occurs due to a faulty
governor. The likely consequence for each motor powered from
this generator is to:
1.
Line fuses and overcurrent relays
"Protective discrimination" means the progressive grading
of sizes/tripping times of:
1.
A 3-phase induction motor is rated at 200 A.Its initial direct- on-line starting
current will be approximately:
1000 A
1.
Inform the bridge about the reason for
blackout, and expected time to restart.
When a blackout occurs: what should be your first reaction?
1.
It satisfies the SOLAS requirements for ship
safety
An electrical power emergency source in a ship is
required because:
1.
Emergency diesel and batteries
1.
Generator overload due to many motors
Choose the group of electrical power supplies that
best fits the identification of "Emergency"
starting at simultaneously
After main power is restored, a timed sequential
restart of motor-driven auxiliaries is necessary to
avoid:
1.
No. 1 diesel and No. 2 diesel
1.
A short circuit occurs between earth faults
and the ventilation fan fuse blows
Choose the group of electrical power supplies that best fits
the identification of "Mains"
An earth fault exists on the blue line of a 100 A bilge pump
circuit. A second earth fault occurs on the yellow line of a
10 A ventilation fan circuit. The likely outcome is that:
1.
A ships 3 - phase a.c. circuit has 440 V and 220 V
transformer linked sections. The effect of a single earth
fault on a 220 V line will cause the following earth lamp
In 440 V section: Two lamps bright. In 220 V
section: Two lamps bright.
indication:
1.
2.
If the A.C. line current in a generator is doubled, the
heating effect in the stator windings will:
3.
Quadruple
1.
Bimetallic strips need time to cool down
1.
Line currents: 0 A, 180 A, 180 A. Trip
A motor is protected by a thermal overcurrent relay. After tripping on
overload it will not be possible to reset the overcurrent relay because
the:
A 3-phase A.C. induction motor is running normally at its rated current of 150
A when a single phasing fault (open circuit) occurs in one line. The likely
condition: trip on overload.
outcome will be:
1.
Short circuit protection.
1.
Initially rise, then reset to the set value.
1.
The main diesel generator or shaft
The function of the fuses in a motor starter circuit is to provide:
When a large motor load suddenly is
disconnected from the switchboard and the
generator is AVR controlled, the voltage will:
generator.
Under normal conditions, the electric power for
services supplied from the emergency switchboard is
supplied from:
1.
AVR and speed governor
1.
Its readiness to perform as specified.
1.
Undue overspeeding.
1.
The diesel speed and excitation current.
1.
0
Prior to synchronising, the generator voltage and
frequency are respectively controlled by:
Regular (at least weekly) testing of the emergency
generator must be performed to check:
Unloading a generator, it is necessary to gradually decrease
the load in order to avoid:
The internal e.m.f. generated in the phase windings of an
a.c. generator is controlled by:
For ideal synchronising, the phase angle difference between
the incomer e.m.f. and the busbar voltage should be:
1.
Circuit breaker operating time
The correct time to synchronise is usually taken to be
when the synchroscope reaches the "5 to 12" position.
This to allow for:
1.
A transformer with 10:1 turns ratio and rated 50 kVA,
2400/240 Volts, 60 Hz, is used to step down the
voltage to a distribution system. The low tension
voltage is to be kept constant at 240 Volts. What load
impedance connected to the low-tension side will
cause the transformer to be fully loaded?
1.15 Ohms
1.
3 phase excitation winding/rectifier
bank/main field winding
A 450 volt 3 phase brushless alternator will have the
following combination of items mounted on the rotor:
1.
10 000 000 Ohms
A 450 volt, 859 kW rated generator has not been in
operation for several weeks. Prior to starting, insulation
resistance readings are taken. The minimum acceptable
insulation resistance reading on the main stator winding to
allow you to proceed with running the generator is:
1.
Governor droop settings on each prime
mover
For two generators running in parallel, their share
of additional load (kW) will be determined by the:
1.
Figure 3.
1.
579.2 kW
Which alternative is correct for
measuring current over the load L?
A three phase alternator is connected singularly to
the main switchboard. The switchboard instruments
show 440 Volts/950 amperes. With a power factor of
0.8 what will be the kW load?
1.
What is Hz the abbreviation for?
Frequency in an Alternating Current (AC)
1.
Wrong installation will result in a major
deviation in measurement
Will it matter to the accuracy of the measurement how you are
installing a resistance element in a thermo-well
1.
Speed governor and voltage regulator
After successful synchronising the kW and kVar loading
are respectively transferred by the following controls:
1.
Hotter due to increased current
1.
Formula 1
1.
To prevent the alternator from "motoring" by
being supplied power from other parallel
It is possible to operate two similar generators in
parallel at equal power (kW) but at different power
factors. The generator with lower power factor will
cause it to run:
P = U x I x Root of 3) x cos (fi) What is the formula for I ?
What is the purpose of the alternator reverse power
trip?
1.
alternator
Reactive load (kVAR)
If you alter the field excitation voltage of one alternator
operating in parallel, this will cause change in that
alternators:
1.
When 3 phase alternators are operating in parallel, it
is very important that the reactive load is evenly
shared so that the total alternator loads are evenly
shared. If the total alternator load is the vector sum
(Y)
of active and reactive loads, which side of the vector diagram shown represents the
reactive load?
1.
Prevent damage to sensitive electronic
components from high voltage tester
Before taking insulation resistance readings of
generator windings the automatic voltage regulators
should be isolated and all semiconductor short
circuited or disconnected in order to:
A star connected induction motor operates on 220 V with power factor 0.7 and efficiency1.
of 82 %. Its output is 8 HP. What is the phase, current and voltage?
I phase is 27.3 Ampere, phase voltage is
127 Volt.
How is the set pressure (opening pressure) adjusted on the cylinder head safety valve of
1.
a diesel engine?
By adjusting the spring pressure.
1.
the thermal resistance fed by the output of
amplifier A
Item No 2 of this Wheatstone Bridge is _____
1.
A voltage gain greater than 100,000
1.
Because the connections in A and B and in
C and D are opposed
Indicate the correct characteristic of the amplifier "A".
The potential of this thermocouple bridge is zero if all
connections are kept at the same temperature. Why is
the indication of the potentiometer zero ?
1.
What will be the binary output at E ?
0
1.
Three phase rectifier.
1.
An electric P-controller.
What is the function of the circuit shown here ?
What control equipment drawing is shown here ?
A six-pole asynchronous motor is connected to a power supply with a frequency of 50 1.
Hz. If the rotor bar frequency is 2.3 Hz, what will be the speed of the motor ?
1.
954 RPM
an operational amplifier.
In this drawing, the triangle marked "A"
represents _____
1.
By C and R1
How is the differentiating action of this PID controller
obtained ?
1.
The rudder position via the trunion
connection.
The second potentiometer of this electric command
system is located in the steering gear. What moves
this potentiometer ?
1.
decreases with time.
1.
None
In these integrator circuits the air flow through the
restrictor and the current through the resistance _____
What is the difference in function between these
electrical and the pneumatic integrators ?
Two 3 phase 4160 Volt, 60 Hz alternators are operated in parallel. The total load of the 1.
the Power Factor of alternator No 2 is
system is 1050 kW with power factor 0.75 lagging. If alternator No 1 is carrying 700 kW
at 80 % power factor lagging _____
lagging 0.658.
1.
3
From the sample diagrams shown, choose the correct
voltage waveform measured across the load.
Alternator (A) 100 kVA runs parallel with alternator (B) 125 kVA, both are 3 phase, 240 1.
V, 60 Hz. The load of A is 60 kW, 90% power factor and the load of B is 80 kW, 70 %
429.8 Amps
power factor. What is the total load ?
If the prime mover of an alternator is a diesel engine, what should the Reverse Power 1.
5 - 12 %
Relay`s pick up setting be ?
1.
infinite input impedance.
An ideal operational amplifier is characterised by _____
What is a high-pass filter ?
1.
A circuit that will only pass high frequency
signals.
1.
B
Which of these formulas is used to calculate
capacitive reactance (Xc) ?
The size of any electrical conductor should be such that in practice, the voltage drop at 1.
full load will not exceed _____
2%
1.
By fitting another resistance in parallel
The resistance characteristic of Platinum is linear. The
resistance characteristic of Nickel is non-linear. How can the
characteristic of Nickel be made linear ?
A six pole asynchronous motor is fed from a 60 Hz circuit and has a slip of 5 %. What is1.
the motor speed ?
1.
1140 RPM
The integrator characteristics.
These graphs are, left, the step input and, right, the output
response of a controller. What characteristics are shown ?
1.
Convert an electric temperature
measurement into a pneumatic signal.
1.
Compensation for changing conductor
The function of this measuring system is to _____
resistance by changing temperature.
The three conductor system used by Wheatstone
Bridge lay-outs is intended to provide _____
1.
R3
1.
The proportional, integration and
differentiation.
Which resistor determines the proportional band on this
electronic proportional integrating controller ?
In the output characteristics (right) of this controller, which
response lines are clearly shown ?
1.
A proportional integrating-differentiating
controller
For which kind of controller are the input and output
characteristics shown here ?
1.
a pure integrator.
The characteristics shown here indicate a ramp input on
the left together with the corresponding output on the right
of _____
1.
A proportional differentiating controller.
For which control instrument are these the
input (left) and the output or response (right)
characteristics ?
1.
A proportional integrating controller.
1.
strong.
For which type of controller are the input and output
characteristics shown here ?
Fitting a restriction R1 in the supply to the
proportional feedback of this PID controller ensures
that for an initial small variation on the input, the
initial response on the output will be _____
1.
A binary flip-flop.
1.
2-3%
What does this symbol represent?
The pick up and the time settings of reverse power relays are adjustable. If the prime
mover of the alternator is a steam turbine what is the trip level setting ?
1.
For this PID controller to act only as a P (proportional)
controller, what should be the arrangement of restricting
valves R1 and R2 ?
R1 fully open, R2 closed