Power Distribution System

The Function Of A Ship's Electrical Distribution System Is To Safely Convey The Generated Electrical Power To Every Item Of Consumer Equipment Connected To It. Probably The Most Obvious Element In The System Is The Main Distribution Centre, I.e. The Ship's Main Switchboard. The Main Board Supplies Bulk Power To Motor Group Starter Boards (often Part Of The Main Board), Section Boards And Distribution Boards. Protection, E.g. Circuit-breakers And Fuses, Strategically Placed Throughout The System Automatically Disconnects A Faulty Circuit Within The Network. Transformers Interconnect The High Voltage And Low Voltage Distribution Sections Of The System.

The Operational State Of A Distribution System Is Indicated By The Monitors For Power, Voltage, Current And By Protection Relays For Over Currents And Earth-faults At Each Main Control Centre. Study The Electrical Power Diagrams For Your Own Ship To See If You Can Relate Them To The Actual Equipment They Represent.
 
The Vast Majority Of Ships Have An Alternating Current (a.c.) Distribution System In Preference To A Direct Current (d.c.) System.
 
The Required Electrical Services Are Broadly Considered As Main And Emergency Supplies.

The Ship's 'Electrical Distribution System For Ships' Is Called A Radial Or Branching System. This Distribution System Has A Simple And Logical Structure. Each Item Of Load Is Supplied At Its Rated Voltage Via The Correct Size Of Cable And Is Protected By The Correctly Rated Protection Device.


Q1. Why A.C  network Is Installed On Ship? Also Explain What A.C System Is Used On Board?
An A.c. Network Is Cheaper To Install And Operate Than A D.c. System. In Particular A.c. Offers A Higher Power / Weight Ratio For The Generation Distribution And Utilisation Of Electricity. Simple Transformers Efficiently Step-up Or Step-down A.c. Voltages Where Required. Three-phase A.c. Is Effectively Converted Into Rotary Mechanical Power In Simple And Efficient Induction Motors.
 
The Majority Of Ships Have A 3-phase A.c., 3-wire, 440 V Insulated-neutral System. This Means That The Neutral Point Of Star-connected Generators Is Not Earthed To The Ship's Hull. For Continental European Vessels, A 380 V, 3-phase System Is Common.

Ships With Very Large Electrical Loads Have Generators Operating At High Voltages (HV) Of 3.3 KV, 6.6 KV And Even 11 KV.  where Equipment Weight Saving Is Important. Distribution Systems At These High Voltages Usually Have Their Neutral Points Earthed Through A Resistor Or Earthing Transformed To The Ship's Hull.

Q2. What Frequency Is Used On Board ? Also Explain How Low Power Supply Is Achived.
The Most Common Power Frequency Adopted For Use On Board Ships And Offshore Platforms Is 60 Hz. This Higher Frequency Means That Motors And Generators Run At Higher Speeds With A Consequent Reduction In Size For A Given Power Rating.

Lighting And Low Power Single-phase Supplies Usually Operate At The Lower Voltage Of 220 V A.c. Although 110 V A.c. Is Also Used. These Voltages Are Derived From Step-down Transformers Connected To The 440 V System.

Q3. What Do You Mean By Distribution System?
The Distribution System Is The Means By Which The Electrical Power Produced By The Generators Is Delivered To The Various Motors, Lighting, Galley Services, Navigation Aids, Etc. Which Comprise The Ship's Electrical Load.

Q4 How Electricity Is Routed To Final Load?
The Electrical Energy Is Routed Through The Main Switchboard, Then Distributed Via Cables To Section And Distribution Boards Then Ultimately To The Final Load Consumers.

Q5 What Are The Protection Provided In The Electrical System?
The Circuit-breakers And Switches Are The Means Of Interrupting The Flow Of Electric Current, And The Fuses And Relays Protect The Distribution System From The Damaging Effects Of Large Fault Currents.