Ship's Electrical System Overview PDF

# Chapter 1 Overview of a Ship's Electrical System - Explain the need for specially designed equipment onboard ships and the effects of the marine environment on such equipment - Identify major components in a marine electrical system - Recall the basics of power management onboard ships - Compreh...

# Chapter 1 Overview of a Ship's Electrical System - Explain the need for specially designed equipment onboard ships and the effects of the marine environment on such equipment - Identify major components in a marine electrical system - Recall the basics of power management onboard ships - Comprehend various electrical diagrams - Comply with regulations governing the operation of marine electrical equipment ## 1.1 The Marine Environment - Marine Engineering now includes the field of offshore engineering as well as traditional seagoing ships. - Those with experience in this industry generally accept that electrical equipment manufactured primarily for shore-based industries are not suitable for installation in a marine environment. - Climatic conditions, vibration, the continuous motion of a ship, temperature and conditions of usage are all contributory factors. ## 1.2 Effects of Inclination - Main propulsion and all auxiliary machinery essential to the ship shall, as fitted in the ship, be designed to operate when the ship is upright and when inclined at any angle of list up to and including 15º either way under static conditions and 22.5° under dynamic conditions (rolling) either way and when simultaneously inclined dynamically (pitching) 7.5° by bow or stern. - The Administration may permit deviation from these angles, taking into consideration the type, size and service conditions of the ship. - The emergency generator and its prime mover and any emergency accumulator battery shall be so designed and arranged as to ensure that they will function at full rated power when the ship is upright and when inclined at any angle of list up to 22.5° or when inclined up to 10º either in the fore or aft direction or is in any combination of angles within those limits. ## 1.2.1 Designed Angles of Inclination | Installations, components | Athwartship Static | Athwartship Dynamic | Fore-and-aft Static | Fore-and-aft Dynamic | |---|---|---|---|---| | Propulsion and auxiliary machinery | 15 | 22.5 | 5(4) | 7.5 | | Safety equipment | 22.5 | 22.5 | 10 | 10 | | Emergency power installation(3) | 22.5 | 22.5 | 10 | 10 | | Emergency fire pumps and their drives | 22.5 | 22.5 | 10 | 10 | | Switchgear | 22.5(2) | 22.5(2) | 10 | 10 | | Electrical and electronic appliances and control systems | 22.5(2) | 22.5(2) | 10 | 10 | > **Athwartship and fore-and-aft inclinations occur simultaneously** > **Up to an angle of inclination of 45º, switches and controls are to remain in their last set position.** > **In vessels designed for carriage of liquefied gases and of chemicals, the emergency power installation is to remain operable with the vessel flooded to its permissible athwartship inclination up to a maximum of 30°** > **Where the length of the vessel exceeds 100 m (328 ft), the fore-and-aft static angle of inclination may be taken as 500/L degrees, where L is the length of the vessel in meters (1640/L degrees, where L is the length of the vessel in feet).** ## 1.3 General Provisions - A ship's electrical system can be divided into 'supply' and 'users' or 'consumers'. - It is sometimes convenient to further divide the 'supply' into those components which 'generate' and those which 'distribute'. ### Generation covers the following: - Prime movers - Electrical generators (a.c. and d.c.) - Starting arrangements - Control devices to maintain correct values of speed, frequency and voltage ### Distribution covers the following: - Main Switchboards - Auxiliary Switchboards - Section Switchboards - Group Starter Panels - Circuit Breakers - Transformers - Cabling - Switches, fuses, etc. ### The 'users' or 'consumers' cover all the machinery, equipment and systems which consume electrical energy, such as: - Motors driving machines (such as pumps) - Heating installations - Lighting circuits - Portable equipment (such as lights, tools etc.) ## 1.3.1 Definitions Relating to Conditions and Electrical Equipment Onboard a Ship ### 1) Normal Operational Condition - It is the condition under which the ship as a whole is in working order and functioning normally. - It also includes machinery, services, means and aids ensuring propulsion, the ability to steer, safe navigation, fire and flooding safety, internal and external communication signals, means of escape, and emergency boat winches. ### 2) Conditions of Habitability - The services are needed to provide minimum living conditions aboard a ship. - Such services include services such as cooking, heating, domestic refrigeration, mechanical ventilation, sanitary and fresh water. ### 3) Emergency Condition - Any services needed for normal operational and habitable conditions are not in working order due to failure of the main source of electrical power. ### 4) Dead Ship Condition - The main propulsion plant, boilers and auxiliaries are not in operation due to the absence of power. ### 5) Main Source of Electrical Power - It is a source intended to supply electrical power to the main switchboard for distribution to all services necessary for maintaining the ship in normal operational and habitable condition ### 6) Main Generating Station - It is the space in which the main source of electrical power is situated. ### 7) Main Switchboard - It is a switchboard which is directly supplied by the main source of electrical power and is intended to distribute energy to the ship's services. ### 8) Emergency Source of Electrical Power - It is a source of electrical power, intended to supply the emergency switchboard in the event of failure of the supply from the main source of electrical power. ### 9) Emergency Switchboard - It is a switchboard which in the event of failure of the main electrical power supply system is directly supplied by the emergency source of electrical power or the transitional source of emergency power and is intended to distribute electrical energy to the emergency services. ## 1.3.2 Electrical Services - Propulsion of the ship, safety equipment and services, navigation, steering, bilge pumping, ballast pumping, fire fighting are all concerned with maintaining steerage way and manoeuvrability. ## 1.3.2.1 Primary Essential Services - Primary Essential Services are those which need to be in continuous operation for maintaining propulsion and steering. - Some of them are as follows: - Steering gears. - Pumps for controllable pitch propellers. - Scavenging air blower, fuel oil supply pumps, fuel valve cooling pumps, lubricating oil pumps and cooling water pumps for main and auxiliary engines and turbines necessary for propulsion. - Ventilation necessary to maintain propulsion. - Forced draft fans, feed water pumps, water circulating pumps, vacuum pumps and condensate pumps for steam plants on steam turbine ships, and also for auxiliary boilers on vessels where steam is used for equipment supplying primary essential services. - Oil burning installations for steam plants on steam turbine vessels and for auxiliary boilers where steam is used for equipment supplying primary essential services. - Azimuth thrusters which are the sole means for propulsion/steering with lubricating oil pumps, cooling water pumps, etc. - Electrical equipment for electric propulsion plant with lubricating oil pumps and cooling water pumps. - Electric generators and associated power sources supplying primary essential equipment. - Hydraulic pumps supplying primary essential equipment. - Viscosity control equipment for heavy fuel oil. - Control, monitoring and safety devices/systems of equipment for primary essential services. - Fire detection and alarm system ## 1.3.2.2 Secondary Essential Services - These are important users that need not be in continuous operation; however they are necessary to maintain propulsion and steering, including a minimum level of safety for dangerous cargoes to be carried. Some of them are as follows: - Windlass - Fuel oil transfer pumps and fuel oil treatment equipment. - Lubrication oil transfer pumps and lubrication oil treatment equipment - Pre-heaters for heavy fuel oil - Starting air and control air compressors - Bilge, ballast and heeling pumps. - Fire pumps and other fire extinguishing medium pumps. - Ventilating fans for engine and boiler rooms. - Services considered necessary to maintain dangerous spaces in a safe condition (inert gas system of an oil carrier, ventilation for Ro-Ro cargo spaces, etc.) - Navigation lights, aids and signals. - Internal communication equipment. - Lighting system - Electrical equipment for watertight and fire-tight closing appliances. - Electric generators and associated power sources supplying secondary essential equipment. - Hydraulic pumps supplying secondary essential equipment. - Control, monitoring and safety systems for cargo containment systems. - Control, monitoring and safety devices/systems of equipment for secondary essential services. - Ambient temperature control equipment. - Other thrusters like boosters, etc. ## 1.3.3 Main/Emergency Electrical Systems - The ship must have an independent emergency electrical system; some of these systems may also fall in the category of essential services. - The main system can be arranged to feed the emergency system under normal operating conditions. ## 1.4 Installation and Basic Maintenance - In order to reduce end-play and avoid hammering during rolling, machines should be installed with their axis of rotation either vertical or in the fore and aft direction. - If they unavoidably have to be placed athwartship, care must be taken to reduce the end-play and to provide suitable-thrust bearings to prevent any hammering action when the ship rolls. - Special attention must also be paid to lubrication of ring-lubricated sleeve bearings. - The usual cause of overheating in electrical joints is loose connections, and to counter this, particularly in view of the ever-present vibration problem, not only should all screws and nuts be effectively locked but they must also be examined periodically and tightened if necessary. - This applies not only to high-current circuits but also to control and shunt circuits, any of which if allowed to become slack may result in erratic operation or a complete failure. ## 1.5 Effects of Temperature - Extremes of temperature will affect the performance and the effective life of any electrical apparatus. - Devices which depend on electromagnetic operation by shunt coils will find that the resistance of the coil increases with temperature and so with less current, the field strength 'H' is reduced. - Contactors and relays may fail to operate correctly if overheated. - The total temperature is governed by the ambient air temperature and the heating effect of the electric current in the windings. - The heating effect, constituting to a temperature rise, is always about the same for similar loads. - The total temperature, which will affect the life of the insulation and the performance of equipment, will be the highest at the maximum ambient temperature. - For unrestricted service the cooling air temperature is 45°C. - For restricted service and vessels intended for northern and southern waters outside of the tropical belt the temperature is 40°C. - Adequate ventilation and avoidance of hot pockets where electrical apparatus operate is important. ## 1.6 Systems and Major Components ## 1.6.1 Generators - This is one of the greatest discoveries of all time where electrical energy - the easiest way to transfer power over great distances, is obtained from mechanical energy which in turn is derived from: - A basic form of fossil fuel namely diesel, petrol and kerosene - Conventional means namely gas, steam, and water turbines - Non-conventional means namely wind, wave and tidal energies - Futuristic means such as nuclear, solar or biomass energy ## 1.6.2 Power Supplies Commonly Available - Modern merchant vessels usually use alternating current systems classified as three-phase three-wire insulated neutral systems, or three-phase four-wire systems. - Large passenger ships have three or four large generators rated at 2MW or more to supply the extensive hotel services on board. - Superheated steam at high-pressure, produced from exhaust gases can also be used to drive steam-turbine generator sets. - A passenger ship is a ship that carries more than twelve passengers. - A passenger is every person other than the master and the members of the crew or other persons employed or engaged in any capacity on board a ship on the business of that ship and a child less than one year of age. - A cargo ship may have two or more main generators typically rated from 350 kW to a few megawatts, which are sufficient to supply the engine room auxiliaries while at sea, and the winches or cranes for handling cargo while in port. - The limited load required during an emergency demands that the emergency generators be rated from about 10kW for a small coaster to about 700kW or more for a cargo vessel. - The shipbuilder must estimate the number and power rating of the required generators by assessing the power demand of the load for all situations whether at sea or in a port. - Electrical power onboard a ship is commonly generated at 440V, 60Hz. - Ships with a very large electrical power demand may be designed to operate at 3.3kV and even 6.6kV or higher. - Normally high-voltage (HV) generators supply power to propulsion systems, bow thrusters, air conditioning compressors, and similar heavy duty equipment. - The British Standard and International Electrotechnical Commission definition of low voltage is that voltage which is between 50V a.c. and 1000V a.c. - Lighting and other domestic supplies usually operate at 110, 115V or 220V a.c.. - Transformers are used to reduce the generated voltage to this safer voltage level. - Occasionally, transformers are also used to step up voltages, to say, 3.3kV for a large bow thruster motor from a 440V switchboard supply. - Batteries for various services operate at 12V or 24V but sometimes, higher voltages are used. ## 1.6.3 Maximum Voltages - 500 Volts for generators, power, galley, and heating equipment permanently connected to fixed wiring - 254 Volts for lighting, heaters in cabins, public rooms and other applications ## 1.6.4 Main Switchboard - The main elements of a marine distribution system are the main and emergency switchboards, power panels / boards, motor controllers, lighting and small power panels / boards. - The system is generally designed such that under all normal conditions of operation, power is distributed from the main switchboard. - The distribution system is designed to keep cable costs to a minimum by distributing supply to power panels located close to the user services. - The main switchboard is generally located near the centre of the distribution system and this is normally the main engine room or machinery control room. - These locations are normally below the ship's waterline or below the uppermost continuous deck of the ship. - In the event of a fire or flooding it is likely that the main generators and switchboard would be disabled. ## 1.6.5 Motor Control Centre (MCC) - The motor control centre consolidates all the motor controlling equipment for all the major motors on board the vessel. - Over-current and overload protection is provided to the motor and its immediate circuitry. ## 1.6.6 Motor Controls - It is often convenient to group motor driven auxiliaries according to their function. - The auxiliary motors would be supplied from grouped motor controllers located either in the engine room, in a machinery control room or in a convenient location close to the auxiliary motors. - On small ships, e.g. tugs, etc., such grouping is not economical and the major ship's auxiliaries are normally supplied directly from the main switchboard. - In this case the motors would be provided with individual starters located adjacent to the motor. - For high-speed vessels where weight is important, minimum cable weight may be achieved using a 'non-distributed' distribution scheme. - Auxiliary motor controls should be arranged in compliance with the general control philosophy applied to machinery control systems. ## 1.6.7 Emergency Services - To ensure that electrical supplies are available to emergency and safety systems, in the event of a main power failure, an emergency generator and associated emergency switchboard will be located above the main deck in a separate space, completely isolated from the main machinery spaces. - Emergency services would be supplied from the emergency switchboard using distributed panels for navigation, safety and emergency lighting services. - Where lighting is concerned, it is important to ensure that a fire or flooding in one area will not cause the loss of lighting supply in other areas or along escape routes and the circuitry must be designed in compliance with the ships general arrangements. ## 1.6.8 Emergency Stop Panel - According to the requirements of the classification societies, additional emergency stop circuits have to be installed for certain consumers at a location that is separate from their installation position, e.g., in order to switch off fans, the fuel or oil pumps in the endangered area if there is a fire. ## 1.6.9 Ship's Auxiliary Services - Auxiliary services on board a ship range from engine room pumps and fans, deck winches and windlasses to general lighting, catering and air-conditioning. - Electrical power is used to drive a majority of these auxiliary services. - The electrical power system on board a ship is designed to provide a secure supply to all loads with adequate built-in protection for the equipment and operating personnel as well. - The general scheme of a ship's electrical power system is common to nearly all ships. ## 1.7 Load Analysis - Load analysis of the ship's electrical systems is a complex exercise and covers all operating conditions of the vessel, such as conditions in normal sea-going, cargo handling, harbour manoeuvring, and emergency operations. ## 1.7.1 Dimensioning the Electrical Network - Figure 1.6 depicts considerations to be taken while the entire electrical system is being designed. - The main factors being the money involved and of course the ship's operating profile. ## 1.8 Power Management Systems - A vessel may have a number of generating sets, a split bus bar and a variable load. - The main switchboard is fitted with a power management system. - This system has various functions to ensure the continuous supply of the ship's electrical systems. - It automatically controls the diesel generators for efficient operation. - A modern PMS must not only ensure safety but also control fuel consumption and emissions. - Power management systems (PMS) have in the past been relay-based, but a programmable electronic system (PES) using a programmable logic controller (PLC) is now more commonly used. - This can also be integrated into a distributed control system (DCS) for supplying information to the bridge. - Automatic synchronising and load sharing is provided for the ship's generator sets. - It is not necessary to have only a diesel-driven generator as the main source of power; there may be other types of prime movers too. - The power management system automatically equalises the incoming generator's frequency with the busbar frequency and energises the generator's air circuit breaker to connect the two circuits at the moment when the parameters like voltage, frequency and phase sequence coincide. - Automatic load sharing then ensures that each generator is equally loaded. ### 1.8.1 Load Demand Monitoring - The total load is monitored and compared with the available on-line generating capacity. ### 1.8.2 Generator Management - Automatic blackout restart and connection of generators is ensured. - The blocking of large motors until the number of running generators is sufficient to supply the starting current for motors and the ship's power demand, is ensured. - In response to varying load, the system will start a standby generator and initiate the synchronising sequence to bring it on-line, or off-load a generator, disconnect it from the bus and stop it when it is no longer required. ### 1.8.3 Load Sharing - The load demand is shared between generating sets which are on-line. - This can be done on a proportional basis according to the rated power and droop characteristics of each set. ### 1.8.4 Frequency Control - The frequency of the bus is monitored and kept within a specified limit by means of raise /lower signals to each generator governor. ### 1.8.5 Load Inhibit - Some systems operate a load inhibit circuit that prevents a sudden increase in load when the generating capacity is not available. - Load shedding, to trip selected loads in a preset sequence if generating capacity is not sufficient, is often undertaken by a system separate from the PMS's automatic control circuit. ## 1.9 Electrical Diagrams - Diagrams are used to accurately portray the electrical system. - Over the years, many techniques have been used to simplify the diagram for the reader. - Symbols were not standardized, and pictorial schematics showed the electrical system in various degrees of accuracy. - Often the illustrator took for granted that his codes could be understood. In effect, there were no industry standards. - Although each diagram might be electrically accurate, it was not developed for uniform individual interpretation. - Today, as electrical systems become more complex, the electrical community has adopted specific standards to allow a more universal comprehension of the electrical circuits they describe. - However, you will still find many variations due to physical constraints, cost, and the broad time span encompassing the mammoth shipping industry. - There are various types of diagrams, which attempt to show how an electrical circuit operates and some types are explained in this chapter. - Symbols are used to represent components / items of equipment. - A diagram always illustrates contacts, switches, and devices in their de-energized position. - The force that changes the position of contacts can come from any number of places. - A normally open or N/O contact means that the contact's magnetic coil, for instance, has not yet been energized. - The shipbuilder provides a complete set of ships' electrical diagrams. - It is important that you study these diagrams to be able to read and understand them completely, and to use them as an aid in locating electrical faults. ## 1.9.1 Basic or Line Diagram - A line diagram is constructed to show the basic operation of the electrical control circuit and explain the process, in a logical order, of the electrical sequence of events. - This diagram does not show the actual wiring present in the system and may even eliminate actual connections not necessary for the understanding of the circuit's operation. - A line diagram generally depicts the following: * The power source supply lines provided by the power circuit, generally running vertically. * The control circuit, containing the controlling devices and the loads, generally running horizontally. * The relationship of the control devices to the loads they control. * The ratings of machines, transformers, batteries, etc. * All feeders connected to the main and emergency switchboards. * Section and distribution boards * Cable information such as insulation-type, size and current carrying capacity * Details of circuit breakers and fuses, etc. ## 1.9.2 Block Diagram - A block diagram shows in simplified form, the main inter-relationships of the elements in a system, and how the system works or may be operated. - Such diagrams are often used to depict control systems and other complex relationships. - These diagrams state the function of each block but usually give no information of the components therein, or how the blocks are interconnected. ## 1.9.3 System Diagram - A system diagram shows the main features of a system and its bounds, without necessarily showing cause-to-effect. - Its main use is to illustrate the ways of operating the system. ## 1.9.4 Circuit Diagram - This type includes basic circuit logic. - Electrical components are confined by 'series and parallel' rules. - These rules are essential in the understanding of the electrical diagram. - Every resistor, motor, coil, or indicating lamp is designed to operate at a specific voltage. - If all these loads require 24 volts d.c. and they are connected in parallel, then the power supply unit can properly provide 24 volts to each device. - If as few as two 24-volt components are connected in series, the 24-volt power supply will not provide enough voltage to operate them properly. - This is due to the basic voltage division rule. - Thus loads are generally restricted to one load per line. - Each component is provided with access to a positive potential and a negative potential. - A circuit diagram shows in full, the functioning of a circuit. - The circuit diagrams of an electrical propulsion system will also provide details of the following: * Ratings of electrical machines, transformers, etc * Cable information such as insulation-type, size and current carrying capacity * Details of circuit breakers and fuses, etc. * Instrumentation and protection devices * Earth-fault indication and protection ## 1.9.5 Wiring Diagram - A wiring diagram shows the detailed wiring and connections between components or items of equipment and in some cases the routing of these connections. - It also shows the approximate position of the components in the actual equipment. - It may be shown completely or simply represented by a block with the necessary terminals clearly marked. - Lines of different thicknesses can be used to differentiate between the power and control connections. ## 1.9.6 Branch Circuit - The circuit extending from the last over-current protective device in the lighting or control panel is called a branch circuit. - The branch circuit can then be further divided into two more circuits within a motor controlling enclosure (motor controller). - These circuits are called the power and control circuits. ### 1.9.6.1 - Power Circuit - The power circuit usually consists of heavier cables used to carry the higher currents necessary to operate large components. - Power circuits can be three-phase a.c., single-phase a.c., or direct current. - The power circuit will always carry the highest current or voltage from the branch circuit. ### 1.9.6.2 - Control Circuit - The control circuit is derived directly from the power circuit. - The control circuit provides power to the timers, relays, switches and other components necessary to control the operating contacts of the main component in the power circuit. ## 1.10 Relevant SOLAS Regulations (Chapter II-1) - Ships shall be designed, constructed and maintained in compliance with the structural, mechanical and electrical requirements of a classification society, which is recognised by the applicable national standards of the Administration i.e., the Government of the state whose flag the ship is entitled to fly. - Electrical installations shall ensure the availability of the following: - All electrical auxiliary services necessary for maintaining the ship in normal operational and habitable conditions, without resorting to use the emergency source of electrical power; - Electrical services essential for safety under various emergency conditions; and - The safety of passengers, crew and the ship from electrical hazards. # Chapter 2 Electrical Safety - Comply with regulations governing electrical safety - Avoid electrical accidents by adopting adequate safety measures - List the fundamentals requirements for safe installation of equipment - Identify safe electrical equipment for hazardous areas - Render first-aid in the unfortunate event of electrical accidents ## 2.1 Compliance with Regulations - Practically every ocean-going ship is registered with a Classification Society and is therefore required to comply with the Rules of the relevant Society. - Ship Classification, as a, minimum, is to be regarded as the development and worldwide implementation of published Rules and/or Regulations which will provide for: - the structural strength of (and where necessary the watertight integrity of) all essential parts of the hull and its appendages - the safety and reliability of the propulsion and steering systems, and those other features and auxiliary systems which have been built into the ship in order to establish and maintain basic conditions on board, thereby enabling the ship to operate in its intended service ## 2.1.1 Other Important International Organisations - Underwriters Laboratories (UL) is a private company that is nationally recognized as an independent testing laboratory. UL tests products for safety and products that pass UL tests can carry a UL mark. - The National Electrical Manufacturers Association (NEMA) is an organization that, among other things, develops standards for electrical equipment. - The National Fire Protection Association (NFPA) is a nonprofit organization which publishes the National Electrical Code. - The intent of the NEC is to describe safe electrical practices. - The American National Standards Institute (ANSI) is a nongovernmental organization that facilitates the development of standards by establishing a consensus among qualified groups. - The Institute of Electrical and Electronic Engineers (IEEE) is an organization open to individual membership and provides a variety of services for its members. It also develops numerous standards for electrical and electronic equipment and practices. - There are two outstanding considerations in the selection and installation of marine electrical equipment: - outstanding reliability and freedom from breakdown for those services which are essential for safety, navigation and propulsion - freedom from fire risks ## 2.1.2 Relevant SOLAS Regulations (Chapter II-1) - Part D- Electrical Installations - Regulation 45 Precautions against shock, fire and other hazards of electrical origin ## 2.2 The Inherent Dangers and Avoidance of Disastrous Consequences - The best safeguard against accidents is a genuine safety culture - awareness and constant vigilance on the part of all those involved, and the establishment of safety as a permanent and natural feature of organizational decision-making. - IMO defines risk as: "The combination of the frequency and the severity of the consequence." - A hazard is a substance, situation or practice that has the potential to cause harm. - The risks we are concerned with are: - The identification of hazards - The assessment of the risks associated with those hazards - The application of controls to reduce the risks that are deemed intolerable - The monitoring of the effectiveness of the controls - The controls may be applied either to reduce the likelihood of occurrence of an adverse event, or to reduce the severity of the consequences. - The risks we are concerned with are: - The health and safety of all those who are directly or indirectly involved in the activity, or who may be otherwise affected - The property of the company and others - The environment ## 2.3 Passive Safety Measures - This is the highest level of safety for personnel, when all systems are in normal operation. - The basic design philosophy of and electrical system must, when built according to SOLAS Requirements, Classification Rules, Regulations or Standards, have an inherent ability to withstand stresses generated externally and within the system. - This ability must giver each particular function, for example, a power supply for a pump, a defined quality or reliability level. - The level is reached through correct system design, application or use of suitable equipment, correct rating and correct installation procedures. ## 2.3.1 Component Quality or Reliability Level - Components must be selected according to their actual use. - The rating must be selected according to the prospective stresses applied on the component by the system at the location where it is installed. - The component must be installed in such a way that its properties as defined above are maintained. ## 2.3.2 Protection against Erroneous Operation - As far as is possible safeguards are built into the electrical system so that a system, component or machine will be 'fail safe' when operational conditions exceed set limits, in terms of voltage, current, temperature, speed, etc. ## 2.3.3 Maintenance - There must be an organised system of maintenance applied to the whole electrical installation. - This involves inspection and testing at regular intervals, and the repair or replacement of any component or part which is found to be defective or malfunctioning. - Only in this way can the electrical installation be relied upon in order to supply electrical energy safely and as demanded by operational requirements. ## 2.3.4 Personnel Protection - All protective measures applied to eliminate potential failures are in fact elements in a personnel protection scheme, as any abnormal situation will reduce the actual safety level. - The most important requirements and their purpose are aimed at the prevention of accidentally touching live parts. - Electrical shocks can be lethal, even at voltages as low as 220V. - The wrong use of tools and other objects can also cause arcs, exposing personnel to short-circuit and similar effects. ## 2.4 Active Safety Measures - When a failure occurs in the electrical installation, the philosophy is that the installation shall only suffer minor operative consequences due to any single system failure. - Measures are also to be taken to limit secondary effects from any system failure, to a minimum. ## 2.4.1 Redundancy Requirements - For particular functions where the reliability level is not considered high enough, the level is normally increased by the introduction of redundant systems ### 2.4.1.1 Essential Users - Users that need to be in continuous operation are duplicated. - These users have separate supplies from the main switchboard. - Main system blackout will interrupt the operation of these users. - Such failures are very rare and if they do occur they are not considered likely to cause major dangers in most installations. ### 2.4.1.2 Important Users - Users are necessary to maintain the main functions of the installation are very often duplicated or partly duplicated. - They are normally supplied directly from the main switchboard or from dedicated distribution switchboards. ## 2.4.2 Circuit Protection - A basic circuit consists essentially of two parts: - The conductor - which carries current around the circuit; and - The insulation - which confines the current to the conductor itself. - The complexity of other faults is beyond the scope of this chapter. ### 2.4.2.1 Short-circuits - A 'short-circuit' occurs when an alternative path of low or negligible impedance becomes available to the applied voltage. - Whenever a short circuit occurs in an unprotected circuit, the current will continue to flow until the circuit is damaged, or until the power is removed manually. - The maximum destructive energy let-through (I't) is a measure of the energy associated with this current. - It is capable of producing enough heat to melt conductors. ## 2.4.2.2 Overload - All components are to be automatically disconnected when overloaded over longer periods of time. ## 2.4.2.3 Loss of System Voltage - Most systems are to be constructed in such a way that they are automatically disconnected from the network when the system voltage disappears. ## 2.5 Fundamental Requirements for Safe Installation of Equipment - From the very early days of electricity there has been an essential requirement for electrical installations to be installed safely, as well as being suitable for the purpose for which they are designed. - Some guidelines are as follows: - Good workmanship and proper materials shall be used throughout the installation; - The equipment shall be installed in such a way as to be accessible for testing, inspection and maintenance as far as is practical; - Joints and connections shall be properly constructed, regarding conductance, insulation, mechanical strength and protection; - Wherever necessary, circuits shall have suitably rated automatic protective devices especially for protection against overcurrent; - Whenever a prospective earth fault current is insufficient to operate the above, a residual current device shall be fitted; - Electrical equipment shall be earthed in such a manner that earth leakage currents will be discharged without danger; - If metal parts of other devices can be touched simultaneously with the above, then they should be earthed; - Single pole switches shall be inserted in phase conductors, only with the exception of linked switches - Circuits supplying electrical equipment shall have effective means of isolation as necessary, to prevent or remove any danger - Safe means of access shall be ensured for persons to operate or attend to installed equipment - Equipment exposed to adverse weather or corrosive conditions shall be designed to prevent any danger from this - No additions to installations shall be made without ascertaining there is sufficient spare capacity for it and that the earthing arrangements are adequate - Testing shall be carried out on completion of the installation, to the requirements as specified in relevant regulations ## 2.6 Dos and Don'ts While Working With Electrical Equipment - Get to know the ship's electrical system and equipment. - Study the ship's diagrams to pinpoint the location of switches and protection devices, distribution boards and essential items of equipment. - Write down this information in a notebook. - Note the normal indications on switchboard instruments so that abnormal operation can be quickly detected. - Operate and maintain equipment according to the manufacturers' recommendations. - Ensure that all guards, covers and doors are securely fitted and that all bolts and fixings are in place. - Inform the Officer of the Watch before shutting down equipment for maintenance. - Remember that it is mandatory to obtain a work permit prior to carrying out any work on equipment that is supplied with voltages greater than 1000 volts. - Most vessels insist on work permits for electrical equipment that operate at even less than 1000 volts. - Switch off and lock all supplies, remove fuses and store them in a safe place. - Confirm that circuits are dead (by using a voltage tester) before touching conductors and terminals. - Make contact with the conductor(s) of a supposedly dead power system, first with the back of one hand. - Proper and foolproof electrical locking would not merely mean switching off the supply by operating the isolation switch / switch fuse handle but by removing the fuses or by mechanically locking the handle in the "Off" position. - Check the instrument used for testing (