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Lesson 24
Switchboard
(配电板)
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The control and distribution of
the electrical energy generated
by generators are effected by
power distribution equipment,
i.e. switchboards.
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Switchboards are either:
(a) Main switchboards(主配电
盘 ), to which the main
generators are connected,
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(b) Emergency switchboards(应
急 配 电 盘 ), to which the
emergency
generator
or
emergency battery is connected,
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(c) Section boards (or Subboards(区域配电板))or
(d) Distribution boards(分配电
板或箱).
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In
small
equipment,
particularly in small cargo
ships, most of the motors can
be fed directly from the main
switchboard,
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but
as
the
size
and
multiplicity(多样性) of services
increase, it becomes necessary
to reduce the number of
outgoing( 引 出 的 ) circuits on
the main board.
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This is done by grouping some
services on one or more section
boards (sometimes referred to
as sub-boards), supplied by a
feeder(馈线、馈电板) from the
main board.
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Still further splitting up(分解)
particularly in the case of
lighting and heating, is usually
necessary and
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and this takes the form of
distribution boards of small
capacity which may be fed
either direct from the main
board or from a section board.
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Generators
Main switchboard
Motor
Motors
G1
Section/sub board
Lighting
G2
Distribution board
Bar-bus
Transformer
E. Generator
E. Lighting
E. switchboard
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Switchboard are divided into
two classes: i.e. those for a.c.
systems and those for d.c.
systems.
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Switchboards may be of the
open type in which all the
essential switch gears(开关设备、
交 换 机 ) are exposed on the
front of the panel(仪表盘, 控
制面板),
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or of the deadfront type(正面无接
线 式 、 不 带 电 式 、 安 全 式 ) in
which all the live(带电的) parts
are installed behind the panels and
only the operating handles and
instruments are on the front.
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The switchboards for a.c.
systems differ from the d. c.
switch gear in that the open
type panels are generally not
permissible.
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Deadfront boards can be either
of two patterns,
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one having manually-operated
switches
and
circuitbreakers( 断 路 器 ) with the
handles on the front of panels
and all the live(带电的) parts
at the rear;
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and
the
other
having
electrically operated circuitbreakers operated by pushbuttons on the front of the
panels.
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Usually
the
panels
are
interlocked with isolators(绝缘
子 、 隔 离 开 关 ) so that the
devices can be made dead(不带
电 的 ) before the doors are
opened.
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The voltages most commonly
adopted for a.c. systems are
either 440V or 220V threephase.
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For d.c. switchboards, there are
ammeters,
voltmeters,
circuitbreakers,
tipping
devices(跳闸装置) and so on,
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but a.c. requires additional
equipment as compared with
d.c., such as frequency meters,
synchroscope, wattmeters,
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voltage
and
current
transformers(电压互感器和电
流 互 感 器 ), ammeter
switches( 安 培 表 的 转 换 开 关 ),
voltage regulators(稳压器、电
压调节器), etc..
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Circuit breakers and switches
will be three-pole as compared
with two-pole for d.c..
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However, in spite of the
additional equipment an a.c.
switchboard is usually smaller
and
lighter
than
the
corresponding( 相 应 的 ) d.c.
board
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because of the higher voltage
and lower currents and smaller
bus-bars(母排、汇流排), etc.
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Electrical supply is always
needed, even if only for lighting.
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So after a ship goes into service
it is extremely rare for the main
bus-bars to be made dead,
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it therefore follows that the
bus-bars
are
continuously
alive( 带 电 的 ) throughout the
life of the ship.
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Even when in a shipyard for
repair, a shore supply will
usually be taken.
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Reading Materials
A. Emergency
Generator supply
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In the event of a main
generating system failure an
emergency supply of electricity
is required for essential services.
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This can be supplied by
batteries, but most merchant
ships have an emergency
generator.
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The unit is diesel driven and
located
outside
of
the
machinery space.
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The emergency generator must
be rated to provide power for
the driving motors of
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of the emergency bilge pump,
fire pumps, steering gear,
watertight doors and possibly
fire fighting equipment.
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Emergency
lighting
for
occupied areas( 居 住 区 ),
navigation lights( 航 行 灯 ),
communications systems and
alarm systems must also be
supplied.
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Where
electrical
control
devices are used in the
operation of main machinery,
these too may require a supply
from the emergency generator.
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Usually only one emergency
switchboard is installed;
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however, for safety reasons
large passenger vessels may
have two emergency sources of
power, thus requiring two
emergency switchboards.
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Emergency
switchboards
normally consist of a generator
control panel, a bus tie and
distribution panel (汇电板和配
电盘) and
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and 24-volt, 120-volt, and 450volt distribution panels in size
and number as required.
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Emergency
generator
switchboards include those
devices noted in the foregoing
for
main
switchboard
generator control panel plus
the following:
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1. A white light to indicate that
the
normal
supply
is
available.
2. A green light to indicate
that all devices are “set up”
for automatic
operation.
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3. A normal supply circuit
breaker, unless the automatic
bus transfer(主送电器) is of the
contactor type.
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4. A feed back switch when the
automatic bus transfer is of the
contactor type.
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It is not usual for an emergency
generator to require paralleling,
so no equipment is provided for
this purpose.
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Automatic start up of the
emergency generator at a low
voltage value is usual on
modern installations.
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B. Maintenance of electrical
equipments
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With all types of electrical
equipment
cleanliness
is
essential for good operation.
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Electrical connections must be
sound( 完 好 的 ， 可 靠 的 ) and
any signs of sparking should be
investigated.
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Parts subject to wear must be
examined and replaced when
necessary.
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The
danger
from
a.c.
equipment in terms of electric
shocks(触电) is far greater than
for similar d.c. voltages.
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Also a.c. equipment often
operates at very high voltages.
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Care must therefore be taken to
ensure isolation of equipment
before any inspections or
maintenance is undertaken.
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The accumulation of dirt on
electrical equipment will result
in insulation breakdown and
leakage currents, possibly even
an earth fault.
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Moisture or oil deposits will
likewise( 同 样 地 ) affect
insulation resistance.
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Regular insulation resistance
measurement
and
the
compiling(汇集) of records will
indicate( 预 示 ) the equipment
requiring attention.
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Ventilation passages or ducts
may become blocked, with
resultant lack of cooling and
overheating.
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Oil deposits from a direct
coupled diesel engine driving an
open generator can damage
windings and should therefore
be removed if found.
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Totally
enclosed machines
should be periodically opened
for inspection and cleaning
since carbon dust will remain
inside the machine and deposit
on the surfaces.
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Brushgear should be inspected
to ensure adequate brush
pressure and the springs
adjusted if necessary.
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New brushes should be ‘bedded
in(研配)’ to the commutator(整
流 子 ， 换 向 器 ) or slipring
shape with fine glass paper(精
细玻璃砂纸).
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Sparking at the commutator
will
indicate
poor
commutation(换向、整流).
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This may require polishing of a
roughened( 粗 糙 的 )
commutator surface.
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The mica( 云 母 ) insulation
between
commutator
segments( 换 向 片 、 整 流 片 )
may require undercutting(剔槽)
if it protrudes(凸出), or simply
cleaning if deposits have built
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up.
Control equipment, such as
starters, will require attention
to contacts which may be worn
or pitted(有凹痕的) as a result
of arcing(电弧放电).
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Contactors( 接 触 器 ， 触 头 )
usually have a moving or
wiping( 磨 擦 ) action as they
come together.
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This helps clean the surfaces to
provide good electrical contact,
and also the arc produced
during closing and opening is
not at the finally closed position.
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The contactor contact surfaces
of frequently used equipment
should therefore be subject to
regular inspections.
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