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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 …“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
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 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 • 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 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 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 • 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 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 • 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 • 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 • #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.
