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Flexible Ship Electric Power System Design
Abstract
This paper discusses new techniques which will
reduce manning requirements and increase the
reliability of continuous service through
automation of functions related to the ship's
electrical system. Its functions include
monitoring and control, automated system
failure analysis and identification, automated
intelligent system reconfiguration and
restoration, and self-optimizing power system
architecture under partial failure.
Introduction
The first electrical power system was installed
on the USS Trenton in 1883 (Ykema 1988).
The system consisted of a single dynamo
supplying current to 247 lamps at a voltage of
110 volts d.c. Until the 1914 to 1917 period, the
early electrical power systems were principally
d.c. with the loads consisting mainly of motors
and lighting. It was during World War I that
230 volt, 60 hertz power systems were seriously
introduced into naval vessels. Since World War
II the ship’s electrical systems have continued to
improve, including the use of 4,160 volt power
systems and the introduction of electronic solidstate
protective devices.
Shipboard Power System
Structure
Navy Ships use three phase power generated
and distributed in an ungrounded delta
configuration. Ungrounded systems are used to
ensure continued operation of the electrical
system despite the presence of a single phase
ground. The voltages are generated at levels of
450 volts a.c. at 60 hertz. The most popular
topology used in Navy electrical system is a ring
configuration of the generators which provides
more flexibility in terms of generation
connection and system configuration. In this
type of topology, any generator can provide
power to any load. This feature is of great
importance in order to ensure supply of power
to vital loads if failure of an operating
generating unit occurs.
Generator switchboards are composed of one or
more switchgear units and are located close to
their associated generators. Further the
generator switchboards are composed of three
sections: one section contains the generator
breaker, generator controls, breaker controls,
and protective devices; the other two sections
contain a bus tie breaker, load center breakers,
and breakers for major loads.
Reconfiguration and
Restoration
System faults must be quickly resolved by
removal of the faulted portion of the system
from the remainder of the system. These faults
could be due to material casualties of individual
loads or widespread fault due to battle damage.
In addition to load faults, casualties can occur to
cables, power generating equipment, or power
distribution buses which can lead to conditions
of having inadequate power generation capacity
for all attached loads.
TABLE 1
Present Monitoring, Control, and Protection Functions
MONITORING PROTECTION
EQUIPMENT Data Available Parameters CONTROL Device Location of
Protection
Device
Generator local and remote current, voltage, phase
angle, power,
frequency, CB status
local and remote circuit
breaker
generator
switchboard
Bus Tie Breaker local and remote voltage, current,
power, CB status
local and remote circuit
breaker
generator
switchboard
Load Center local and remote current, voltage local and remote circuit
breaker
generator
switchboard
Power Distribution Panels local current, voltage local circuit
breaker,
fuse
an enclosure
centrally
located to
loads that it
supplies
Frequency Conversion
Unit
local and remote voltage, current,
power, frequency,
phase angle,
temperature
local and remote circuit
breaker
frequency
converter
switchboard
Bus Tie Breaker local and remote current local circuit
breaker
frequency
converter
switchboard
Non-vital Loads local current local circuit
breaker,
fuse
generator
switchboard,
load center
switchboard,
power
distribution
panel,
frequency
converter
switchboard
Non-vital Loads
(Part of load shedding
scheme)
local current local, automatic circuit
breaker,
fuse
power
distribution
panel,
generator
switchboard,
load center
switchboard,
frequency
converter
switchboard
Vital Loads local current local circuit
breaker,
fuse
power
distribution
panel,
generator
switchboard,
load center
switchboard,
frequency
converter
switchboard