Shipboard Electrical Distribution

1
Shipboard Electrical Distribution

• Shifting the Electric Plant to a Normal Full
  Power Lineup.

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Topics

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

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Primary Power Characteristics

• US Residential
• 115 VAC Power
• 1 phase, 60 Hz frequency
• Grounded system
• US Navy
• 450 VAC Power
• 3 phase, 60 Hz frequency
• Ungrounded system

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Primary Power Characteristics

• 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)

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Basic 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)

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Basic Components

• Bus Transfers
• Allow transfer of load from one bus to another
  (normal -gt 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)

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Basic 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

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Electrical 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 DGs
• Designed to provide power to vital systems during
  a casualty

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The Electric Plant
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Electrical 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

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Other AC Generation Systems

• 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

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DC Generation Systems

• Battery chemical potential due to dissimilar
  metals (Pb vs. PbO2) in presence of electron
  bridge (electrolyte)
• SSMG converts AC lt-gt DC (large machine with an
  AC end DC end)
• Static Inverters solid state to replace SSMGs
• Rectifier converts AC -gt DC

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Degaussing

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

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Safety Considerations

• 1 On-the-job KILLER of sailors
• Working in vicinity of energized gear requires
  COs 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.

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Any Questions?