Marine Engineering Study Materials

MEO Orals on Marine Electro Technology Function 5- Part 7

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

It is essential, when machine has been exposed to weather, or when accidentally immersed.

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

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.

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

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.

By injecting current with injectors

By reducing frequency

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

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

Adjusting number of poles by means of selector switch.

Reference:

Oral Guide by – MIN ZAR TAR