22 November 2016

ORAL QUESTIONS AND ANSWERS FOR ETO - PART - 1

Oral on Marine Electro Technology  Part - 1



1. What documents to give to surveyor for switch board survey ?
Voltmeter, Wattmeter, Ammeter Calibration test result
ACB test result (Survey result)
Control Circuit Safeguard test results (Safety trips and Alarm test results)
Maintenance reports
IR test results of each terminal; all 440 V and 220  V main circuit

2. Data to be given Surveyor for electrical survey ?
Voltmeter, Wattmeter, Ammeter calibration test result
ACB test result (Survey result)
Control Circuit Safeguard test results (Safety trips and Alarm test results)
Maintenance reports
IR test results of each terminal : all 440 V and 220 V main circuits
IR test results of all motors & their safety factors, such as:
> Test date, time, place
> Voyage No.
> Ambient temperature
> Weather condition, hot or humid
> Machine is hot or cold

3. Difference between DC and AC generators ?
DC generator has commutator and AC generator has slip ring or brush less.

4. What is drop test ? ( Volt drop test)
It is a kind of test for exploring the open circuit fault, short-circuit fault of an armature winding or a set of field windings
It is more reliable check than the growler test.

5. Testing in electric machines ?
Insulation test (Meggar test)
Continuity test
Voltage test
Current test

6. How many types of motor starter ?
Direct on line starter
Star delta
Auto transformer

7. What is static electricity ?
Electricity produced on dissimilar materials through physical contact & separation.
Out going material negative, remaining material positive. After having high potential spark occur.
This is occurs in thin oil. Explosion occurs when tank cleaning operation and gas freeing operation.

8. Protection against accumulation of static charges ?
Bunker pipes are electrically bonded and from ship earthing arrangement to shore.
Inert gas maintains above cargo in the tanks.
C.O.W operation must be start after pumping out 1 m3 to make sure no water remain in the tank.

9. What is open loop in control system ?
The loop is open, there is no feedback and the action of the controller has no reference to the result it produces.
An open loop is a manual process where by information is not feed back to the control system. A man is required to sight visually or read display information and then make an adjustment.
Manual control gives satisfactory results. Carelessness of the operator may lead to an end product of result that fails to meet the requirements.
The arrangement may then decide to install automatic control. The controller must replace the human brain.

10. The close loop automatic control system
In practical automatic control systems, the controlled variable must first be measured.
This may require both a detecting (sensing) element and a measuring element, or two may be combined in a single unit; the measured value is then compared with the desired value in the comparison element.
The output from the comparator, commonly called the error, causes the amplifier to vary its output in such a way as to reduce the error.

11. What is closed loop in control system ?
In an automatic process the closed loop is formed by the sensor, which feeds back information of the final process. This feedback or closed loop, return into a mixing point or comparison point where it compares itself against reference or set point signal. Any deviation between these two signals will alter or adjust the control mechanism.

12. What is data logger ?
The data logger is capable of producing a printer record of off limit conditions.
It can also produce a printed log of plant sensors at predetermined intervals or on demand.

13. What is meant by automation ?
Any or all of the combined processes used aboard ship that have the ability to control work, notify the operator of its status and warn of malfunctions.
This allows less people to control more machinery in a more accurate and efficient manner.

14. Action when an electrical machine is flooded with seawater ?
Machine is disconnected from power sources and dismantled
All salt deposits washed out with freshwater
If deposited with oily bilge water, wash out with Electro Cleaner
Should be heated with lamp, and enclosed or covered up to retain the heat
Moisture should be escaped, by lifting the cover continuously or periodically
Hottest part of the machine shall not exceed 90°C, while heating
IR readings and temperatures taken regularly, until constant value reach about 1 mega ohms
Then spray the machine with insulation vanish
Assemble and out in service with low load, if possible

15. Why drying out of electrical machine ?
It is essential, when machine has been exposed to weather, or when accidentally immersed.

16. Short, open and grounded circuits ?
Short circuit:
A low resistance path that actually shorten the intended path for the flow of current
Open circuit:
The path for the flow of current is broken. A switch s one method of creating an “open” intentionally
Grounded circuit:
A circuit that has come in contact with the earth, by coming in contact somewhere in itself, or by a conductor which is connected with the earth

17. What is shore connection on ships ?
Shore connection box is provided at convenient position, to receive shore power supply, so that ship’s generators can be shut down, in port or during Dry Docking.

18. What are Lloyd’s requirement on shore connection ?
Connection box contains a circuit breaker or isolating switch with fuses
Provided full information of supply system, normal ship voltage and frequency for AC current
Main Switch board must be provided with a link switch or a circuit breaker, voltmeter, ammeter, and an indicator to show that the cable is energized
For 3-phase supply with earth neutral and earthing terminal must be provided, for connecting the hull to shore side.
A phase sequence indicator is necessary to ensure correct connections
Means shall be provided for checking polarity, and terminals should be labeled

19. How will you check the frequency of shore power supply ?
Shore power supply connection box shows phase sequence of shore power generator with bright and dark lights
Frequency can be check at Main Switchboard, after shore supply is ‘on’ through link switch or circuit breaker.

20. What are Common faults in DC Generator and Motors ?
Sparking at brushes
Overheating
Failure to excite

21. Causes of Sparking at Brushes ?
Wrong brush position
Dirty commutators
Brushes not properly bedded
Incorrect spring pressure on brushes
Wrong grade of brush
Overloading

22. Causes of Overheating ?
Overloading
Blocking up of ventilation passages with dirt

23. Test for over current trip ?
By injecting current with injectors

24. Test for Reverse Power Trip ?
By reducing frequency

25. What is Ward Leonard System ?
Used for fine control of shunt motor speed from zero to full in either direction
Able to give the motor a robust torque characteristic
Can be used for motors of electric steering gears of ships with DC power
Used on ships with AC power for deck machinery such as windlass, mooring winch etc.
Working motor, which powers the steering gear, windlass or other equipment is a DC machine, because speed control of these made easy

26. How Ward Leonard System works ?
A DC generator is driven by AC squirrel cage induction motor.
Output voltage of DC generator is applied as power supply to armature of working motor.
Speed and direction of working motor varies with magnitude and direction of applied voltage
Output voltage of DC generator is increased or decreased by Potentiometer, as magnetic field strength is altered by changing the field current to field windings of the generator
As output voltage of the generator varies, speed of the working motor also varies
Change of current flow direction, also by Potentiometer, through the field poles of the generator will cause the change in direction of generated current, supplied to the working motor and thereby also the running direction of the motor

27. How to control speed of AC motor ?
Adjusting number of poles by means of selector switch.

28. What are motor earthing symptoms ?
440V, low insulation alarm
Earth lamp signal

29. What are the effects of motor earthing ?
Over heat
Burn out
Get the smell
Noisy

30. Specifications of fuses on ships ?
Amperage of the circuit (AC/DC)
Type of fuse wire (Tin or lead wire)
Standard Wire Gauge (SWG)

31. Specifications of battery on ships ?
Voltage
Ampere/hour
Size
Type (Lead Acid or Alkaline)

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Reference:

Oral Guide by – MIN ZAR TAR
marineengineeringonline


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ORAL QUESTIONS AND ANSWERS FOR ETO - PART - 1
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