Calculations of short circuit current in electrical power system for a commercial vessel

The electrical power demand aboard ship increases according to its day to day operational needs. The electrical power demand will vary according to the ship type and propulsion system. To meet the power demand, two or more main generators are used. The main generators generate the electrical power and supply the main switchboard. The function of a ship's electrical distribution system is to safely convey electrical power to every item of equipment connected to the main switchboard. The ship electrical power system includes all equipments which are relevant to electrical power generation and distribution. There are many differences between the shipboard and terrestrial electrical power system. The most significant diffeerence is that the distance between power generating equipment and electric equipment of ships is short, and the voltage of power supply is low, so the lower circuit impedance influences short circuit current. The shipboard power system design generally requires the tasks which are load analysis to define the generator size and number, selection of main voltage and frequency, sizing the feeder cables for required ampacity and for limiting the voltage drops, short circuit calculation, selection of protection devices and their breaking capacities based on short circuit calculations. Load analysis is made to size the generator capacity and number. 3-phase voltage levels in ships are 440V-690V-3.3kV–6.6kV etc. Starting with the load balance, the power required is calculated, necessary size of generators and transformers is selected. The short-circuit current of the main switchboard is calculated. Short circuit current analysis is essential and important for selection of proper protection devices. According to the analysis, shipboard electrical power system is designed to allow securely cruising of the ship. In this study, a fishing vessel which has low voltage electrical power distribution system is studied. Short circuit current calculations in ship electrical power system is examined. Load flow analysis is carried out under different ship operational conditions for the short circuit current calculations. Maximum and minimum short circuit currents in ship electrical power system is calculated on different buses in ship distribution system under different operational conditions. 3-phase short circuit current calculation is carried out, in compliance with the prescriptions of the Std. IEC 61363. The short circuit analysis is often required to estimate the short circuit currents in different buses in the system to determine the proper capacities of protection devices. According to the short circuit analysis results, the main protective devices which are important and necessary for design of the main swtichboard are selected. Load flow analysis and short circuit analysis for the fishing vessel electrical power system are performed by using ETAP program. The analysis results are explained.