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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 Sub-boards(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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G1G1

G2G2

GeneratorsGenerators

E. GeneratorE. Generator

Bar-busBar-bus

Main switchboardMain switchboard

E. switchboardE. switchboard

LightingLighting

Distribution boardDistribution board

E. LightingE. Lighting

MotorMotor

MotorsMotors

Section/sub boardSection/sub board

TransformerTransformer

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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 circuit-breakers(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 circuit-breakers operated by push-buttons 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 three-phase.

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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 450-volt 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 up.

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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.