Principles of naval engineering - Historic Naval Ships Association

CHAPTER 20SHIPBOARD ELECTRICAL SYSTEMSShipboard electrical systems include a greatvariety of equipment which provides numerousservices indispensable to the operation of amodern naval ship. These systems distributepower throughout the ship for offensive and defensiveweapons, the ship's movement, and shipboardhabitability. Since the systems and equipmentutilizing electric power are often underthe cognizance of a division other than theelectrical division, a joint responsibility frequentlyexists for the operation, maintenance,and repair of electrical systems and equipment.This chapter provides some information onbasic electrical theory and gives a brief descriptionof shipboard electrical systems andequipment.BASIC ELECTRICAL THEORYThe word electric is derived from the Greekword meaning amber. The ancient Greeks usedthe word to describe the strong forces of attractionand repulsion that were exhibited by amberafter it had been rubbed with a cloth. Sincescientists are still unable to define electricityclearly, and since many of the phenomena whichoccur cannot be completely explained, theoriescan only be postulated from the reactions observed.Through research and experiment, scientistshave observed and described many predictablecharacteristics of electricity and have postulatedcertain rules which are often called "laws."These laws of electricity, together with theelectron theory, are the basis for our presentconcepts of electricity.ELECTRON THEORYEvery atom is primarily an electrical systemwith high speed planetary electrons orbitingaround its nucleus. The electron, whose negativecharge forms a natural unit of electricity, isbound to the atom by the positive charge withinthe nucleus.The electrons in the outer orbits of certainelements are easily separated from the positivenuclei of their parent atoms. Should an outsideforce be applied, one of these loosely boundelectrons will be released from the parentatom, thus becoming a free electron, and travelto another atom. It is on this ability of an electronto move about from one atom to anotherthat the electron theory is based.Elements such as silver, copper, gold, andaluminum have many loosely bound electronsand are considered to be good conductors ofelectricity. In materials used as insulators,electron flow from one atom to another isrelatively non-existent, since the planetary electronsin the outer orbital shells are more tightlybound to their parent nuclei.Ordinarily an atom is most likely to be inthat state in which the internal energy is at aminimum, having a neutral electrical charge.However, if an atom absorbs sufficient energyfrom am. outside source, loosely bound electronsin the outer orbital shells will leave the atom.An atom that has lost or gained one or moreelectrons is said to be ionized . If an atom loseselectrons it becomes positively charged and isreferred to as a positive ion ; if an atom gainselectrons it is referred to as a negative ion andis said to have a negative charge. Apositive ionwill attract any free electron in its surroundingsin order to reach a neutral state.STATIC ELECTRICITYWhen two bodies have unlike charges, onepositive and the other negative, an electricalforce is exerted between the two. This force iscalled a static charge or an electrostatic force .A static charge can easily be produced bythe force of friction when two materials are492