Difference between Circuit Breaker and Fuse

Circuit breaker:
Has switching actions to close the circuit or to open the circuit, and
has a trip circuit if load current exceeds the set value.
After tripping, circuit breaker can be reused without replacing any part.

Fuses:
Have only breaking function, and fitted in the circuit to protect the circuit from damaging effect of high current flow.
It breaks the circuit by melting the fuse metal itself.
After breaking, the blown fuse must be renewed.

Actions carried out when Electrical Machines (Motor) flooded with Sea Water

When Electrical Machine is flooded with SW:

• Machine is disconnected from power sources and dismantled.
• All salt deposits washed out with FW.
• 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 m Ω.
• Then, spray the machine with insulation vanish.
• Assemble and put in service with low load, if possible.

Explain a Dashpot used as a Time Delay device in Over load trips

Dash pot:
Dashpots are fitted for overload trips to get time delay action, so that breaker will not be opened, due to momentary current surge.
When load current is in excess, it attracts plunger of the solenoid.
Plunger or piston moves up against the displacement of viscose oil or silicone fluid, through a small hole on the piston.
Time lag depends upon hole size, and viscosity of oil.
Load current setting for trip is about 25% above maximum, but should not exceed 50%.

Explain Shore connection onboard a ship with class requirements and regulations

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 Dry Docking.

Lloyd’s Requirements:
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 Switchboard must be provided with a link switch or a circuit breaker, voltmeter, ammeter, and an indicator to show that the cable is energised.
For 3-phase supply with earth neutral, an 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 labelled.

What are Ship (Marine) Battery Room Safeties and Maintenance carried out

Battery room inspection and maintenance:
Battery installation and its charging rectifier checked.
Battery room environment must be dry and well ventilated.
Battery tops shall be clean and dry, and terminal nuts must be tight and a smear of petroleum jelly applied to prevent corrosion.
Electrolyte at proper level, and shall have correct value of specific gravity by checking with a hydrometer.
Rubber gloves and goggles used when handling electrolyte.
Charging equipment checked for dirt, overheating, loose connection and correct functioning of indicators.
Ventilation arrangement for battery locker checked. Battery installation of both lead acid and alkaline needs good ventilation.
Since both type generates hydrogen gas during charging, no smoking and naked light allowed.
Steel works and decks adjacent to lead acid battery, should be painted with acid proof paint.
[For Cad-Ni cell, alkaline resistance paints.]
Battery Room Safety Arrangement:

Safety is provided by:
Proper ventilation
Prevention of heat source for ignition.

Ventilation:
Independent exhaust fan provided.
Inlet duct should be below battery level, and outlet at top of the compartment.
Prevention of heat source for ignition:
No naked light and no smoking.
Uses of externally fitted light or flameproof light.
Cables of adequate size and they are well connected.
Never placed Emergency Switchboard in this room.
Use insulated spanner and plastic jug for distilled water, to prevent short-circuit.
Room temperature, maintained at 15 ~ 25°C.

MEO Class 4 E-Pariksha important numericals of Ship construction and MET

• Ship Construction
• Marine Electro Technology