By : Tejeshwar Singh Rana, Chief Officer-Merchant Navy & Associate Editor-ICN
Marine Electricity or Marine electrical power is a vital part of a ship’s operation. Without marine electricity, ships would not be able to run any of the machinery and cannot perform their core purpose of sailing from one place to another.
We cannot define the term “Marine Electricity” as a whole. To understand its meaning, first, we need to understand them separately.
Marine – Here, the term “marine” refers to ships, ports, drydocks, and other structures which cater to the shipping of cargo by sea.
Electricity – It is a type of energy resulting from the existence of charged particles (such as electrons or protons), either statically as an aggregation of charge or strong as flowing current.
The electricity which is produced, supplied and distributed onboard ship, port, drydock, shipyard for running or repair of the cargo and passenger ships is referred to as Marine electricity.
Marine Electricity Generation
Marine electricity generation can be done onboard ships by diesel, shaft or steam-driven generators.For ports, shipyards, and structures located inland, marine electricity is utilized from the electricity supply of the land-based power generation plants.Unlike land, the ship’s generator has insulated neutral points i.e. its neutral is not grounded or connected to the ship’s hull. This is done to ensure all the essential machinery are up and running even if there is an earth fault.
The ships plying in the international waters generally have 3 phase D.C. supply with 440v insulated neutral system. Ships like RORO, passenger etc. having large electrical load requirements are installed with high voltage operating gensets in the range of 3KV to 11KV.
On land, the frequency of the power supplied can be 50 or 60 Hz depending on different parts of the world. On ships, 60hz frequency is adopted as standard practice which helps hundreds of motors on a ship run at higher speed even if they are of smaller size.The supply which is at 440v is stepped down using a transformer to 220V or 110V for lights and low power signal equipment.
All the electrical equipment onboard ships are similar to land however, they are upgraded to withstand the rigorous atmosphere of the sea and moving ship to withstand humid surroundings, high temperatures, salty and corrosive atmosphere, vibration, etc.
The electrical onboard ships can be divided into five specific systems:
Main Switchboard System
Emergency Switchboard System
The generator system consists of an alternator and driver for the alternator which can be a diesel-driven or steam-driven engine.Many ships are equipped with shaft generator where the rotation of the main engine of the ship is used to operate the alternator and generate additional electricity.
Marine generator engine
The Power generated by these marine generators is transported to the Main switchboard using Busbars. There are no electrical wire connections inside the main and emergency switchboards on ships for connecting Power supply from generators to these switchboards. All high voltage and high current systems are connected by bus bars.
Main Switchboard System
The main switchboard is considered as the distribution hub of the ship’s electrical system taking power from the power generator and distributing it to the power consumer spread all over the ship. It provides a power supply to all important ships machinery with 440V.A part of the main switchboard is provided with a 220V supply via a stepdown transformer. It includes bridge equipment, navigation lights, radio communication equipment, etc. The power from the auxiliary switchboard is used to charge the battery which is used for emergency lights.
Emergency Switchboard System
An emergency generator is required to be operational at all times once the main generator fails. This emergency generator will start automatically and provide power to the emergency switchboard.All the emergency equipment supply is connected to the emergency switchboard. The emergency switchboard is also divided into two sections – 440V and 220V, providing supply to appropriate machinery and equipment.
The Distribution system comes after the switchboard and consists of the following
These boxes are enclosed and made up of metal to supply power to localized parts of the ship’s machinery.Motor starter boxes: There are hundreds of motor operating several mechanical machinery onboard ship. Each group of motors is provided with a motor starter boxes containing their “On & OFF” switch along with safety devices. Local gauges for amperage and temperature are fitted on the starter panel.
Electrical supply system
Shore connection boxes: When the ship is in a port with emission control requirements or during the dry-docking process where the ship generator cannot run, shore power is taken for running ship machinery. Shore panel is provided which is usually located near accommodation entry or near the bunker station to easily accept shore supply cable;
Lighting distribution panel
The lighting distribution panel supplies power to lighting systems, accommodation systems, small heating appliances, circuits, and motors of 1/4 HP or less.
Emergency switch-off panel : For safeguard of ship machinery and personnel, various Emergency switch Off Panels are provided at different locations for shutting down machinery and equipment in an emergency situation.
The main aim of installing a distribution system is to have an operational, alarm, and safety consol for individual or group of machinery. Power is supplied through circuit breakers to large auxiliary machinery at high voltage. For smaller supply fuse and miniature circuit breakers are used.
Marine generator working principle
lighting distribution panel
The generator works on the principle that when a magnetic field around a conductor varies, a current is induced in the conductor.The generator consists of a stationary set of conductors wound in coils on an iron core. This is known as the stator. A rotating magnet called the rotor turns inside this stator producing a magnetic field. This field cuts across the conductor, generating an induced EMF or electro-magnetic force as the mechanical input causes the rotor to turn.The magnetic field is generated by induction (in a brushless alternator) and by a rotor winding energized by DC current through slip rings and brushes.
The power generation and transmission process is explained in this article.
Safety of marine electricity system
The Safety of marine electrical systems includes safekeeping of personal from electrical shock and damage to the machinery due to electrical malfunction.
For safety against electrical shock, check our article on – How to Minimize the Risks of an Electrical Shock on a Ship?For machinery safety, depending on the size and power rating of the equipment, a relay, circuit breaker or fuse can be used which prevents the electrical equipment from overcurrent or overheating.
Temperature gauges, RPM of the motor, direction indicator, Amperage meter, etc. are different equipment used locally to monitor the performance of the electrical machinery or equipment and to understand the general health of the machinery.