Shipboard Shipboard Electrical Electrical

DistributionDistribution…“…“Shifting the Electric Shifting the Electric Plant to a Normal Full Plant to a Normal Full

Power Lineup.”Power Lineup.”

TopicsTopics

• Primary Power • Electrical Distribution System• Components of systems• Selective tripping• Other AC power generation systems• DC Power generation• Safety Considerations

Primary Power Primary Power CharacteristicsCharacteristics

• US Residential• 115 VAC Power• 1 phase, 60 Hz frequency• Grounded system

• US Navy• 450 VAC Power• 3 phase, 60 Hz frequency• Ungrounded system

Primary Power Primary Power CharacteristicsCharacteristics

• Why AC?• More power than DC for same size

• Why 3 Phase?• More power than single phase• Can operate with only 2 phases -

redundancy• Why ungrounded?

• NOT Safety• Reliability: at least two faults are required

to cause system failure (grounded systems fail with one fault)

Basic ComponentsBasic Components

• Ship Service Generators• Primary source of power is rotating-field

generator• Powered by prime mover

• SSTG (steam)• GTGS (gas)• EDG (diesel)

• Switchboard• Metal enclosure that serves as distribution

center (contains buswork, breakers, instruments, etc)

Basic ComponentsBasic Components

• Bus Transfers• Allow transfer of load from one bus to

another (normal -> alternate)• ABT: senses voltage loss quickly and auto

transfers supply to alternate source to ensure continuity of power

• MBT: manual transfer, used for non-vital loads

• Disconnects• Used for infrequent connections (shore

power)

Basic ComponentsBasic Components

• Circuit Breaker• Used as switches to connect buswork• Trip open and break circuit if unsafe

condition (over current, under voltage, under frequency)

• Arc Fault System• Fuse

• Simplest protective device• Fusible strip of wire melts to provide

protection• Must be replaced once blown

Electrical DistributionElectrical Distribution

• Ship Service Distribution System• Provides normal and alternate power• Power from generators switchboards

sent to loads, power panels, etc.• Parallel requirements for closing circuit

breakers• Emergency Power Distribution

• Normally supplied by DG’s• Designed to provide power to vital

systems during a casualty

The “Electric Plant”The “Electric Plant”

Electrical DistributionElectrical Distribution

• Casualty Power Distribution system• Use of portable cables for temporary

routing of power in severe casualty• Selective Tripping

• Principle under which faults are isolated as close to the fault as possible and furthest from power supply

• Done via fuses, switches, and breakers (most current system is arc-fault)

• Vital vs. Non-vital loads

Other AC Generation Other AC Generation SystemsSystems

• 115 VAC, single phase, 60 Hz used for smaller loads• Used for lighting, outlets, etc.• Step-down transformer

• 400 Hz Power• Most of electronics including fire control &

sonar use 400 Hz• 400 Hz MG used to convert 60Hz to 400

Hz

DC Generation SystemsDC Generation Systems

• Battery: chemical potential due to dissimilar metals (Pb vs. PbO2) in presence of electron bridge (electrolyte)

• SSMG: converts AC <-> DC (large machine with an AC end & DC end)

• Static Inverters: solid state to replace SSMG’s

• Rectifier: converts AC -> DC

DegaussingDegaussing

• Circulation of DC current around the hull to reduce the magnetic signature.• Degaussing stations• Magnetic exploders

Safety ConsiderationsSafety Considerations• #1 On-the-job KILLER of sailors• Working in vicinity of energized gear

requires CO’s permission• NUMEROUS electrical safety precautions

• Electrical Tagout to de-energize where possible• Rubber gloves• Insulated tools• Diamond deck• CPR qualified personnel• Removal of jewelry/metal objects• Etc.

Any Questions?Any Questions?