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Файл:English for marine electro-technical officers. Supplementary book. Учебное пособие
.pdf
41
Answer the questions:
1. Does the drive power for compressors, pumps and
fans aboard come from electric motors?
2. What are d.c. commutator motors used for?
3. Where are single-phase a.c. motors used?
4. What are high power synchronous a.c. motors
used for?
5. How many components has the induction motor?
6. What are they?
7. What does the rotor consist of?
8. Where are the commutator bars set in?
Words and expressions (3.2, 3.3)
load range
диапазон изменения нагрузок
forced-draught fans
вентилятор с принудительной
тягой
application
применение
smooth
гладкий, ровный
uniform
единообразный, однородный
interior
внутренняя сторона
exterior
внешняя сторона
godliness
безупречный
dissipation
распыление, разложение
duct
канал, проток
suction
всасывание
42
3.2. Speed control
The standard cage-rotor a.c. induction motor operates as
an almost constant speed drive over its load range. This feature
is satisfactory for most of the ship's auxiliary services supplying power to ventilation fans and circulating pumps.
Variable speed control is necessary for cranes, winches,
windlass, capstans, forced-draught fans etc. Ship's electric propulsion with electronic speed control may use d.c. motors or
a.c. induction motors for low / medium power applications.
Large power electric propulsion, e.g. for a passenger cruise
ship, will use a.c. synchronous motors.
Two main forms of speed change / control are available:
- pole-changing for induction motors to give two or
more fixed speeds, e.g. 2-speed forced-draught fans and 3speed winches;
- continuously variable speed control, e.g. smooth control of deck cranes, winches and electric ship propulsion using
variable frequency.
3.3. Maintenance
The maintenance requirements for cage-rotor induction
motors are very simple:
- keep insulation resistance high and contact resistance
low;
- lubricate correctly and maintain a uniform air gap;
43
- ensure both the interior and exterior are always clean
and dry.
Provided these requirements are met, an induction mo-
tor should give trouble free service during its long life.
For all motors, cleanliness is next to godliness. A regular cleaning routine is required to remove harmful deposits of
dust, dirt, grease and oil from both inside and outside the motor. The cleaning of the external surface is especially important
for totally enclosed motors which run continuously. The heat
generated in these motors is removed through the external surface. A thick layer of dust will reduce the heat dissipation and
result in very high temperatures. Internal dust and dirt in open
ventilated motors must be regularly removed by blowing or
extraction and ventilation screens and ducts cleared out.
If motors are to be blown out, the air used must be absolutely dry and the pressure should not be more than 1,75 bar.
If the pressure is higher than this it forces the dust into the
winding insulation rather than removing it.
When blowing out a motor remember to cover up other
machines in the area to protect them from flying dust. Suction
cleaning is better than blowing out.
Answer the questions:
1. How does the standard cage-rotor a.c. induction mo-
tor operate?
2. Is variable speed control necessary for cranes, winch-
es, windlass, capstans?
44
3. What are two main forms of speed change / control?
4. What are the maintenance requirements for cage-
rotor induction motors?
5. What is the most common cause of induction motor
failure?
6. Why is the cleaning of the external surface especially
important for totally enclosed motors which run continuously?
7. Suction cleaning is better than blowing out, isn’t it?
8. How often should a motor be cleaned?
45
4. AUXILIARY ELECTRICAL SERVICES
Words and expressions (4.0, 4.1, 4.2)
generated electric power
вырабатываемая мощность
impressed current cathodic
protection method
метод катодной защиты
наложенного тока
battery supplies
питание от батареи
to meet the safety and comfortable of illumination
для обеспечения безопасного
и удобного освещения
to deteriorate
ухудшаться
watts input
входная мощность
luminous efficiency
светоотдача
screw and bayonet fittings
резьбовое и байонетное
сочленение
4.0. Introduction
To ensure a safe working environment, together with
off duty comfort in the accommodation quarters on board your
ship, a considerable proportion of the generated electric power
is absorbed in the auxiliary services.
46
Lighting of the ship's deck areas, engine room and accommodation to meet specified levels of illumination is provided by various light fittings (luminaires) designed to work
safely in their particular locations.
The hotel services for food storage, preparation and
cooking, together with accommodation air-conditioning and
laundry services, are essential for the general maintenance of
the mariner.
4.1. Ships’ lighting
Historically, the original application of electricity in
ships was for lighting.
The minimum illumination standards for crew spaces
are specified in “The Merchant Shipping (Crew Accommodation) Regulations)”.
The luminous efficiency of a light fitting is defined as
the ratio of lumens watt.
Lamp end caps are many and various but the most
common types are screw and bayonet fittings.
4.2. Incandescent lamps
The most common lamp used for general lighting is the
simple filament type. A current is passed through the thin tung-
47
sten wire filament which raises its temperature to around
3 000 °C when it becomes incandescent (it glows).
The glass bulb is filled with an inert gas such as nitrogen or argon which helps to reduce filament evaporation to allow an operating life expectancy of about 1 000 hours. Lamp
power ratings are available from 15 W to 1 000 W.
Answer the questions:
1. What is absorbed to ensure a safe working environ-
ment on board ship?
2. What is lighting of the ship's deck areas, engine room
and accommodation provided by?
3. Where are the minimum illumination standards for
crew spaces specified?
4. What is the ratio of lumens watt?
5. What are the types of lamp end caps?
6. What lamps are used for general lighting?
7. What are lamp power ratings?
Words and expressions (4.3, 4.4)
incandescent lamp
лампа накаливания
simple filament type
простая нить накала
to reduce filament evapora-
уменьшить испарения нити
48
tion
накала
coiled-coil filament
биспиральная нить накала
tungsten -halogen type
вольфрамо-галогенный тип
sealed glass bulb (tube)
стеклянный запаянный
баллон (трубка)
to cause an arc discharge
through the gas
вызывать искровой разряд
в газе
desired light output
необходимый световой
выход
iron-cored induction (choke
coil)
индукция сердечника
switch-start circuit
коммутационно-пусковая
цепь
transformer quick-start
circuit
цепь быстрого запуска
трансформатора
surge voltage
выброс напряжения
strike (el.)
зажигать (дугу)
power factor correction
(PFC)
корректировка коэффициента
мощности
radio interference
suppression (RIS)
подавление помех
mercury lamp
ртутная лампа
49
4.3. Discharge lamps
The light output from a discharge lamp is generated by
the flow of current in an electric arc between two electrodes
through a gas and metal vapour inside a sealed glass bulb
or tube.
The most common metal vapours employed in discharge lamps are:
- Mercury (as used in a fluorescent tube) and
- Sodium.
Low and high-pressure types of mercury and sodium
lamps are available.
A suitable voltage applied between the electrodes of
a discharge lamp causes an arc discharge through the gas. This
ionization of the gas either creates visible light directly or by
secondary emission from a phosphor coating on the inside wall
of the lamp glass.
The discharge lamp current must be carefully controlled
to maintain the desired light output and some form of current
limiting ballast is required.
4.4. Navigation and signal lights
The number, position and visible range of navigation
lights aboard ships are prescribed by the International Maritime
Organization (IMO) in their “International Regulations for
50
Preventing Collisions at Sea”. In the UK, the National Authority for maintaining marine safety standards is the MCA (Maritime and Coastguard Authority).
By far the most common arrangement is to have five
specially designed navigation running lights referred to as
Foremast, Mainmast (or Aft mast), Port, Starboard and Stem.
Two anchor lights, fitted forward and aft, may also be
switched from the Navigation Light Panel on the bridge. The
side lights are red for Port and green for Starboard while the
other lights are white. For vessels length more than 50 meters,
the masthead light(s) must be visible from a range of six nautical miles and the other navigation lights from three nautical
miles.
To achieve such visibility, special incandescent filament lamps are used each with a typical power rating of 65 W
but 60 W and 40 W ratings are also permitted in some cases.
Due to the essential safety requirement for navigation
lights it is common practice to have two fittings at each position, or two lamps and lampholders within a special dual fitting.
Each light is separately supplied, switched, fused and
monitored from a Navigation Light Panel in the wheelhouse.
The electric power is provided usually at 220 V a.c. with
a main supply fed from the essential services section of the
main switchboard.
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