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Shipboard Electrical Distribution. …“Shifting the Electric Plant to a Normal Full Power Lineup.”. 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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Shipboard electrical distribution

Shipboard Electrical Distribution

…“Shifting the Electric Plant to a Normal Full Power Lineup.”


Topics
Topics

  • Primary Power

  • Electrical Distribution System

  • Components of systems

  • Selective tripping

  • Other AC power generation systems

  • DC Power generation

  • Safety Considerations


Primary power characteristics
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


Primary power characteristics1
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)


Basic components
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)


Basic components1
Basic 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 components2
Basic Components

  • Circuit Breaker

    • Used as switches to connect buswork

    • Trip open and break circuit if unsafe condition (over current, under voltage, under frequency)

  • Fuse

    • Simplest protective device

    • Fusible strip of wire melts to provide protection

    • Must be replaced once blown


Electrical distribution
Electrical Distribution

  • Ship Service Distribution System

    • Provides normal and alternate power

    • Power from generators switchboards sent to loads, power panels, etc.

  • Emergency Power Distribution

    • Normally supplied by DG’s

    • Designed to provide power to vital systems during a casualty



Electrical distribution1
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)


Other ac generation systems
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


Dc generation systems
DC 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


Safety considerations
Safety 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.



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