The AC’s & DC’s of Electric Motors A.O.Smith Motor …

1 AC s & DC s of Electric MotorsINCLUDES:BASIC PRINCIPLESMOTOR CONSTRUCTIONAC induction MOTORSSELECTING THE PROPER MOTORMOTOR REPLACEMENTQUESTIONS & : The AC's and DC's of Electric Motors3 TABLE OF CONTENTSBASIC MaterialsMagnetic ElectricityConductivity of MaterialsFirst GeneratorElectromagnetInductionWork, Power and DefinedHorsepower DefinedWatts DefinedWatts per Horsepower RelationshipOhms Law Tables and FormulasEnergy ExplainedAlternating and Direct CircuitWhere Power Comes FromDistribution SystemsAlternating Current GeneratorCycles and FrequencyPolyphase PowerMOTOR CONSTRUCTIONR otor and WindowBall AClass BClass FClass HMotor Plate ..14AC induction MOTORSS eries (Universal).

2 15 Path of Current FlowUsesSingle Phase PhaseStarting WindingRunning WindingStarting SwitchSpecial Purpose MotorsCapacitor Motors (Types)Capacitor ExplainedElectrical ConnectionsShaded Pole MotorPole ConstructionPole Shift ExplanationRepulsion-Start induction MotorConstructionShort Circuiting Ring; GovernorPolyphase of 3-Phase PowerConstructionNEMA Dual Voltage ConnectionsStar ConnectionDelta ConnectionSELECTING THE PROPER MOTORHow to Determine What Motor to Power SupplyHorsepower and Speed RequirementsBest Motor for the JobFrame Size NeededTorque ConsiderationsWhat Enclosure is NeededBearing Type RequiredDirection of RotationMotor MountingShould Thermal Protection be AppliedTypical Speed Torque Motor Selection REPLACEMENTD etermining Trouble.

3 The AC's and DC's of Electric MotorsMAGNETISMMan s discovery of the phenomenon ofmagnetism is shrouded in mystery and has it that a shepherd named Magnes,while tending his flock on the island of Crete,found his iron-tipped staff held to the ground bysome invisible force. Digging just below the sur-face, he found a rock that exhibited this strangepower of was a lodestone a natural magnet that we know now contained an oxide of iron. So,according to the legend, the city of Magnesia inAsia Minor took its name from this wanderingshepherd, the ore in the rock was called mag-netite, and the natural phenomenon has eversince been called magnetism all a legacy thousands of years, people believed thatmagnets had magic power to cure diseases, and toperform other remarkable feats.

4 Today we knowthat the superstitions about magnets are not truebecause we have learned much more about mag-nets themselves. But we still cannot explain whatthe mysterious force called magnetism really only know how it have certain important characteris-tics. They attract iron and some steel alloys. Amagnet has a north seeking pole and a southseeking pole. This is why a compass indicatesdirection. The north-seeking point of the compassneedle turns toward the earth s north ancient Chinese were the first to capitalizeon this principle in developing the first crudecompass and by the time Columbus sailed fromSpain in 1492, the compass was being used as anaid to navigation throughout the civilized magnets as with people, oppositesattract.

5 The north pole of one magnet will clingto the south pole of another magnet, but two northpoles placed near each other will tend to push themagnets , steel, nickel and a few other materialscan be magnetized. Because soft iron holds itsmagnetism only a short time, it is called a tempo-rary magnet. On the other hand, steel holds itsmagnetism very well and is used to make perma-nent magnets. Certain special alloys make mag-nets much more powerful than iron or steel. Oneof these is alnico, which is a combination ofiron, nickel and aluminum, and sometimes cobaltand is a special magnetic field aroundevery magnet. It is the area in which the magnet spulling force is effective. The greatest pull or attraction is at the two poles of the magnet, andthere are invisible lines of force, like soundwaves, extending from one pole to the other.

6 SeeFig. 1. for a graphic example of this , the iron filings line up just like the lines offorce that exist between the two poles of the mag-net. Later on we will find out why a magnet isnecessary in a magnetism, electricity is a form of energybut, although we have learned a great deal abouthow it works, we can t define it completely got its name in 1600 when SirWilliam Gilbert, personal physician to QueenElizabeth I of England, coined the new word from electron, the Greek word for amber. Amber is ahard yellowish to brownish translucent fossil resinchiefly used for ornamental purposes but it wasthe first substance in which electricity had can be either static or current. If it is stored and not moving, we call it staticelectricity.

7 A charge of this kind may be built upin certain substances by friction. If you walkbriskly across a heavy carpet and then touch ametal railing, a light switch, or even shake handswith someone, you may get an unexpected shock. NSBASIC PRINCIPLESFIGURE 1 Stiff PaperHorseshoeMagnetIron : The AC's and DC's of Electric Motors5 Some materials carry Electric current betterthan others. Those that carry it well are called conductors. All metals are fairly good conduc-tors, but copper wire is most often used to materials that do not carry electricitywell are called non-conductors , or insulators. Among these are paper, glass, wood and hotels place a large rubber mat in front ofelevator doors to reduce or eliminate the staticelectricity which guests may build up by frictionbefore they press the elevator button.

8 Glass insu-lators are used on power lines, and rubber handgrips are often found on pliers and other sockets are made of porcelain, another non-conductor, to prevent Electric first evidence that electricity could begenerated by machine came from a Germannamed Otto von Guericke. In 1660, he built thefirst static Electric generator, using a large ball ofsulphur mounted on an axle. By rotating it andrubbing his dry hand on the surface, he found thatthe ball became charged sufficiently to attractpieces of paper, feathers, and other Franklin, of kite, key and lighteningfame, believed that electricity existed in either apositive (plus) or negative (minus) state. His idealed to the discovery that in Electric charges, aswell as with magnets, unlikes attract and theory that electricity could move or flowwas proved in the late 1700 s as a result of theexperiments of Luigi Galvani.

9 Another Italianscientist, Alessandro Volta, developed the firstbattery, which was called the voltaic pile in hishonor. This battery provided a steady source the 1820 s a Danish scientist, HansChristian Oersted, used a battery to prove thatelectricity can produce magnetism. (See Fig. 2)A short time later, Andre Ampere, a Frenchman,demonstrated that a coil of wire acts like a naturalmagnet when a current is sent through , a piece of iron or steel placed insidethe coil also becomes magnetized. (See Fig. 3)Try it yourself. Wind a piece of wire around andaround a nail many times. Then connect the wireto a battery and you will have what is known as anelectromagnetic coil. The nail will act as a mag-net, but only while the current is experiments of the English scientist,Michael Faraday, eventually led to the develop-ment of the first Electric power generator.

10 Fromreading about the work of Oersted and Ampere, heknew that an electrical current passing through acoil of wire creates a magnetic field. Then, heasked himself, what would happen if a coil of wirewere moved past a magnet? He answered his ownquestion by proving that a current of electricitywould be produced in the wire as it passed by themagnet. In other words, the magnet would induce a current in the now that we have covered the mostimportant facts about magnetism and electricity,we are ready to discuss how Electric energy ismeasured and how it is , POWER AND ENERGYA few basic terms are commonly used in dis-cussing electricity and 2 FIGURE 3 Current FlowCurrent FlowStiff PaperLinesof FluxWireElectricalSourceElectricalSource NLines of : The AC's and DC's of Electric MotorsFirst of all, there is a unit of work.