Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:English for marine electro-technical officers. Supplementary book. Учебное пособие
.pdf
61
ardous areas. However, special electrical equipment is permitted and this chapter will provide a guide to the range and
maintenance of such explosion (Ex) protected equipment.
5.0. Electrical testing in hazardous areas
All electrical apparatus and associated circuits are required to be tested periodically in accordance with a definite
testing routine with recorded test results.
Insulation resistance, earth loop resistance and earth
continuity resistance tests are required to be made, the last two
in relation to the setting or rating of the protective devices associated with the apparatus and its circuitry.
It is important that insulation resistance tests are NOT
made in such a way that the safety devices and insulation used
in intrinsically safe apparatus and circuits are damaged by excess test voltages.
No apparatus should be opened in a danger area until it
has been made dead and effective measures (e.g. locking-off
the isolating switch) have been taken to prevent its being made
live again inadvertently.
Where, for the purpose of electrical testing, it is necessary to restore the power supply before the apparatus is reassembled, tests should be made using a suitable gas detector and
continued during the operation to ensure that the combustible
does not approach the explosive limit.
62
Unless the hazardous area can be made gas-free or otherwise safe, or the electrical equipment is removed from the
area, then insulation resistance testing should be carried out
using a 500 V d.c. tester of certified intrinsically safe (Exi) design.
The testing and maintenance of flameproof or intrinsically safe equipment should be entrusted only to competent
persons who have received instruction in the special techniques
involved.
The body material of instruments and tools required for
maintenance purposes should be designed so that they will not
make a hot spark when dropped.
The energy output of all intrinsically safe instruments
should be so small that they do not produce hot sparks. An insulation tester has a drooping characteristic to prevent high currents and may be intrinsically safe when applied to circuits of
small inductance or capacitance but a risk may arise when such
energy-storing properties of a circuit have an appreciable value.
Where such instruments are used the test leads should
be firmly connected throughout and on completion of the test
they should not be detached until the circuit has been discharged through the testing instrument (leave the tester for one
minute after test is finished).
63
5.1. Maintenance of Ex-protected apparatus
Maintenance of such apparatus must not, in any way,
cause its operation to be less safe than in its original certified
state.
This most important point means that the maintenance
must be carried out by a competent person. Temporary lashups, refitting with wrong sized components (e.g. lamps), failing
to employ the correct number of cover bolts etc., is absolutely
forbidden.
The inspection and maintenance of Exd (flameproof)
enclosures for luminaires, switches, junction boxes, pushbuttons, etc., requires meticulous care.
The following example gives a guide to the inspection
and maintenance points as applied to a flameproof luminaire:
Corrosion
This will reduce the enclosure strength. To ascertain the
extent of corrosion, remove dirt, loose paint and surface corrosion with a wire brush. If only the paintwork is deteriorating,
the enclosure should be repainted to prevent further corrosion.
Bolts
Make sure that there are no missing bolts. This is particularly important on flameproof luminaires because a missing
64
bolt will invalidate the certification. Replacement bolts must be
of equivalent strength as originals (usually high tensile steel).
Mountings
Ensure all mountings are secured. Corrosion and vibration are severe on ships and can cause premature failure.
Flamepaths
Examine the flamepath for signs of corrosion or pitting.
If the flamepath needs cleaning, this should be done with
a non-metallic scraper and / or a suitable non-corrosive cleaning fluid.
Cement
Examine the cement used around lampglass assemblies
both inside and outside. If the cement is eroded, softened or
damaged in any way, advice should be sought from the manufacturer regarding repair. If deterioration of the cement has occurred, a complete new lampglass assembly should be fitted.
Lampglass
Check lampglass; if cracked or broken a complete new
lampglass assembly should be fitted. Clean the lampglass.
65
When reassembling an Exd enclosure you must ensure
that the following points are covered:
Lightly grease all flamepaths and threaded components
with an approved form of non-setting silicone grease. Care
must be taken to ensure that blind tapped holes are free from
accumulated dirt or excessive grease which can prevent the
correct closure of flamepaths, or cause damage to the tapped
components. Fit new lamp of the correct rating.
Ensure bolts are not over-tightened as this can distort
flamepaths, cause excessive stress on lampglasses or distort
weather proofing gaskets, if fitted, allowing the ingress of liquids and dusts. of the installation, particularly the classification
of the area if it is hazardous and that the correct rating of lamp
is fitted.
Remove any build-up of dust on the luminaire, this can
cause overheating as well as acting as a corrosive agent.
Before attempting any maintenance work on Exd
equipment check for any particular inspection and overhaul
instructions given by the manufacturer.
Check the luminaire is installed in accordance with the
requirements.
Answer the questions:
1. What kinds of resistance are required to be made?
2. How can you use electrical devices in dangerous areas?
66
3. Who should the testing and maintenance of flame-
proof or intrinsically safe equipment be entrusted to?
4. Why does an insulation tester have a drooping char-
acteristic?
5. What does the inspection and maintenance points
as applied to a flameproof luminaire include?
67
6. ELECTRICAL SURVEY REQUIREMENTS
Words and expressions (6.0, 6.1, 6.2)
complete engine survey
полный осмотр двигателя
occur
случаться, происходить
Rules and Regulations
for the Classification
of the Ship
Правила по классификации
судов
electrical survey guidance
руководство по осмотру
электрооборудования
International Convention
for the Safety of Life at Sea
(SOLAS)
Международная Конвенция
по охране человеческой жизни
на море
to improve the safety of
shipping
улучшить безопасность
судоходства
to adopt
принимать
requirements
требования
supplementary
дополнительный
precautions
меры предосторожности
6.0. Introduction
The electrical equipment aboard ship is inspected and
tested during the complete engine survey which occurs every
68
four years. Such a survey is prescribed under the Rules and
Regulations for the Classification of the Ship.
The electrical survey guidance given in this chapter is
based on the periodical Survey regulations of Lloyds Register
of Shipping, London. Other classification societies have their
own rules which, although similar to Lloyds, should be consulted prior to an electrical survey.
6.1. SOLAS
The International Maritime Organization (IMO), which
met for the first time in 1959, is a specialised agency of the
United Nations devoted to maritime affairs. Its main interests
can be summed up in the phrase “safer shipping and cleaner
oceans”.
Of all the international conventions dealing with maritime safety, the most important is the International Convention
for the Safety of Life at Sea, better known as SOLAS, which
covers a wide range of measures designed to improve the safety of shipping.
The Convention is also one of the oldest of its kind: the
first version was adopted in 1914 following the sinking of the
Titanic with the loss of more than 1,500 lives.
Since then there have been four more versions of SOLAS. The present version was adopted in 1974 and entered into
force in 1980.
69
The Convention in its consolidated edition dated 1997
has eleven chapters.
Electrical regulations are part of Chapter II-l which outlines the requirements for Ship construction — sub-division
and stability, machinery and electrical installations.
This Chapter has five Parts as follows:
Part A. General
Part В. Sub-division and stability
Part C. Machinery installations
Part D. Electrical installations
Part E. Additional requirements for periodically unattended machinery spaces
The electrical installations (Part D) is sub-divided into
regulations as:
Regulation 40
Regulation 41
Regulation 42
General
Main source of electrical power and lighting systems
Emergency source of electrical power in passenger
ships
Regulation 42-1 Supplementary emergency lighting for
ro-ro passenger ships
Regulation 43 Emergency source of electrical power in
cargo ships
70
Regulation 44 Starting arrangements for emergency
generator sets
Regulation 45 Precautions against shock, fire and other
hazards of electrical origin.
There are some extracts from SOLAS concerning electrical equipment:
Chapter II-1 — Construction — Subdivision and stability,
machinery and electrical installations
The subdivision of passenger ships into watertight
compartments must be such that after assumed damage to the
ship's hull the vessel will remain afloat and stable. Requirements for watertight integrity and bilge pumping arrangements
for passenger ships are also laid down as well as stability requirements for both passenger and cargo ships.
The degree of subdivision — measured by the maximum permissible distance between two adjacent bulkheads —
varies with ship's length and the service in which it is engaged.
The highest degree of subdivision applies to passenger ships.
Requirements covering machinery and electrical installations are designed to ensure that services which are essential
for the safety of the ship, passengers and crew are maintained
under various emergency conditions.
Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]