Shipboard Shipboard Electrical Electrical Distribution Distribution …“ …“ Shifting the Electric Shifting the Electric Plant to a Normal Full Plant to a Normal Full Power Lineup.” Power Lineup.”
Dec 27, 2015
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
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.