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Procedure for Ships Electrical Equipment Maintenance
With all types of electrical equipment cleanliness is essential for good
operation. Electrical connections must be sound and any signs of
sparking should be investigated. Parts subject to wear must be examined
and replaced when necessary. The danger from a.c. equipment in terms
of electric shocks is far greater than for similar d.c. voltages. Also a.c,
equipment often operates at very high voltages. Care must therefore be
taken to ensure isolation of equipment before any inspections or
maintenance is undertaken.
The accumulation of dirt on electrical equipment will result in
insulation breakdown and leakage currents, possibly even an earth fault.
Moisture or oil deposits will likewise affect insulation resistance. Regular
insulation resistance measurement and the compiling of records will
indicate the equipment requiring attention. Ventilation passages or
ducts may become blocked, with resultant lack of cooling and
overheating. Oil deposits from a direct-coupled diesel engine driving an
open generator (usually d.c.) can damage windings and should therefore
be removed if found. Totally enclosed machines should be periodically
opened for inspection and cleaning since carbon dust will remain inside
the machine and deposit on the surfaces.
Brushgear should be inspected to ensure adequate brush pressure
and the springs adjusted if necessary. New brushes should be 'bedded in'
to the commutator or slipring shape with fine glass paper. Sparking at
the commutator will indicate poor commutation. This may require
polishing of a roughened commutator surface. The mica insulation
between commutator segments may require undercutting if it protrudes,
or simply cleaning if deposits have built up.
Control equipment, such as starters, will require attention to contacts
which may be worn or pitted as a result of arcing. Contactors usually
have a moving or wiping action as they come together. 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. The
contactor contact surfaces of frequently used equipment should
therefore be subject to regular inspections.
Safety precautions
Work on electrical systems and equipment is considered a specialised work and must be undertaken only by qualified personnel from the ship’s staff or shore contractors.
Work on electrical equipment in an area where an explosive atmosphere may be present requires special precautions and permission of the Master. He shall ensure that qualified persons are doing the work, in compliance with regulations in force and with adequate safety precautions in place. The Master shall ensure that personnel are supervised and all measures are taken to avoid any accidents or injuries from such work. Reference is to be made to the relevant sections of the Safety and Environmental Procedures.
Work Performance
Whenever work is to be carried out on electrical equipment, or on equipment powered by electricity, in a gas dangerous zone, the electrical supply of the equipment has to be isolated. Warning signs must be posted adequately.
The use of portable electrical equipment or wandering leads is prohibited unless the zone is gas free for hot work and a hot work permit is issued. Intrinsically safe equipment shall be used within their maker’s parameters and company regulations only.
Cold Work on Electrical Equipment
Work shall not be carried out on any apparatus or wiring, nor shall any flammable – proof or explosion-proof enclosures be opened, nor the special safety characteristics provided in connection with standard apparatus be impaired, until all voltage has been cut-off from the apparatus or wiring concerned. The voltage shall not be restored until work has been completed and safety measures have been fully re-instated.
Hot Work on Electrical Equipment
A Hot Work Permit (SAF04) must be issued as per company regulations. Work is permitted provided that the area has first been made safe and certified gas free and no hazardous situation exists – such safe situation should be maintained in that condition as long as the work is in progress. No such work shall be left unattended or without supervision. All regulatory and company safety precautions shall be taken.
High Voltage Systems (Defined here as Voltages exceeding 1000 volts)
All maintenance and testing of high voltage equipment must only be carried out by qualified staff, strictly in accordance with the Company Safety Regulations and the Permit to Work documentation must be completed prior to commencement of any maintenance.
Work by Contractors
The Master shall ensure that whenever contractors are employed, they must be qualified professionally for the work. Arrangements must be such that their understanding of and compliance with all safe working practices are ensured and that they are fully qualified to do the work effectively and they are supervised and controlled by an officer. Checks must be made regularly to ensure that work is being done professionally, that time is not wasted and that correct spares and materials are used when required.
Verification
It is of vital importance for the safe execution of the work on electrical equipment and fittings comply with all regulations and recommendations in force. The materials used shall conform to the regulations and certification provided where applicable.
Circuit Breakers
Main Circuit Breakers are to be clearly labelled to ensure that engine room staff do not inadvertently trip or try to close an incorrect circuit breaker.
Documentation
The planning for electrical work in a gas dangerous zone including safety precautions taken, shall be recorded in the log book and by use of the company Hot Work procedures, checklist and certification.
Related Info:
- A.C. motors for ships machinery
Supplying alternating current to a coil which is free to rotate in a magnetic field will not produce a motor effect since the current is constantly changing direction. Use is therefore made in an induction or squirrel cage motor of a rotating magnetic field produced by three separately phased windings in the stator. ...
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Use of A.C. generators
A coil of wire rotating in a magnetic field produces a current. The current can be brought out to two slip rings which are insulated from the shaft. Carbon bushes rest on these rings as they rotate and collect the current for use in an external circuit. Current collected in this way will be alternating, that is, changing in direction and rising and falling in value. To increase the current produced, additional sets of poles may be introduced....
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D.C. motors for ships machinery
When a current is supplied to a single coil of wire in a magnetic field a force is created which rotates the coil. This is a similar situation to the generation of current by a coil moving in a magnetic field. In fact generators and motors are almost interchangeable, depending upon which two of magnetic field, current and motion are provided.....
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Use of D.C. generators
A current is produced when a single coil of wire is rotated in a magnetic field. When the current is collected using a ring which is split into two halves (a commutator), a direct or single direction current is produced. The current produced may be increased by the use of many turns of wire and additional magnetic fields....
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Emergency power supply for ships machinery operation
In the event of a main generating system failure an emergency supply of electricity is required for essential services. This can be supplied by batteries, but most merchant ships have an emergency generator. The unit is diesel driven and located outside of the machinery space .
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Maintenance requirement for ships electrical equipment
With all types of electrical equipment cleanliness is essential for good operation. Electrical connections must be sound and any signs of sparking should be investigated. Parts subject to wear must be examined and replaced when necessary. ...
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Choice of batteries for ships machinery spaces - Lead acid and alkaline batteries
The battery is a convenient means of storing electricity. It is used on many ships as an instantly available emergency supply. It may also be used on a regular basis to provide a low-voltage d.c. supply to certain equipment.....
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Ships battery maintenance guidance
The electrolyte level should be maintained just above the top of the plates. Any liquid loss due to evaporation or chemical action should be replaced with distilled water. Only in an emergency should other water be used. It is not usual to add electrolyte to batteries.....
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Operating characteristics of battery for ships machinery spaces
Having been 'discharged' by delivering electrical power a battery must then be 'charged' by receiving electrical power. To charge the battery an amount of electrical power must be provided in the order of the capacity.....
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Insulation resistance measurement
Good insulation resistance is essential to the correct operation of electrical equipment. A means must be available therefore to measure insulation resistance. Readings taken regularly will give an indication as to when and where corrective action, maintenance, servicing, etc., is required....
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Use of navigational light circuits
The supply to the navigation lights circuit must be maintained under all circumstances and special provisions are therefore made. To avoid any possibility of accidental open circuits the distribution board for the navigation lights supplies no other circuit.....
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Ward—Leonard speed control system
As a very flexible, reliable means of motor speed control the Ward-Leonard system is unmatched.The system is made up of a driving motor which runs at almost constant speed and powers a d.c. generator .....
- Danger of electric shock to human body
The resistance of the human body is quite high only when the skin is dry. The danger of electric shock is therefore much greater for persons working in a hot, humid atmosphere since this leads to wetness from body perspiration.....
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