畢業(yè)設(shè)計(jì)-110kv變電站一次系統(tǒng)設(shè)計(jì)-預(yù)覽頁
【正文】 mag the armature would bee locked and no further motion would be possible． It is necessarythereforeto prevent the unlike poles from being aligned． In a direct current electric motorthis is done by a device called a mutator which reverses the electron flowchanging the magic poles of the armature at each halfturn． This causes the armature to move on to the new poles of attractionpleting a full rotationorcycle． In an alternating current electric motorthe stationary portion is called a stator and the rotating portiona rotor． with alternating currentthe flow of electrons reverses at rapid intervals． The intervals are timed to change the stator and rotor poles simultaneously so that the rotor continues to move in a circleor cycle ． In the United Statesalternating current electric motors are timed to plete 60cycles per secondabbreviated 60cpsbut in Europe they are timed for 50cycles per second． The property of electromagism is also vital to the production of electrical power． Electricity from chemical action－ the cell or battery－ is suitable only for special and limited uses． Generators based on electromagismhoweverproduce sufficient cheap electricity to supply most of the world1s needs． Not long after the discovery that a magic field could be created by an electric currentthe English scientist Michael Faraday discovered that the reverse was also truea current could be created by a magic field． When a closed loop of wire moves through a magic fieldan electromotive force is created． This causes a current d electrons to flow through the wire and is the basis for generating electricity． Because it is electromotive force that is producedthe power of generators is described in terms of voltstile units of measurement for emf ． To generate emfthe wire must cut the lines of force in the magic field if the wire moves parallel to themno emf is produced． Alsothe faster the wires are made to movethen greater the production of emf ． For this reasona rotarycircularmotion is used in a generator rather than a reciprocatingup－ and－ down or back－ and－ forthmotion－－ it is much easier to maintain a rotary motion at－ high speeds． A generator contains a Statora stationary magwith a rotor placed between its north and south poles． As the rotor turnsthe wires in it cut the lines of force in the magic add of the stator． With each half－ turn the current flow is reversed． This is what produces alternating currentin which the electron flow rapidly changes direction over and over again The rotor is turned by a turbinea machine with huge blades which are generally moved by water or Steam． Steam for an electric power plant can be obtained from the heat supplied by burning coal or oil or by nuclear fission． The enormous size of modern generators and the speed with which the rotor can turn mean that electric power of very high voltage can be produced． As much as half a million volts can be transmitted over high voltage lines to substations． There the voltage is reduced to Strengths that can be used in factories or homes． In the United States the customary voltage for household use has bee 110－ 120vsince it was discovered that higher voltages could cause fatal accidents． 22Ov is still supplied for some heavy－ duty useshoweversuch as for operating an electric st
公司管理相關(guān)推薦
鄂ICP備17016276號-1