Siemens STEP 2000 Course - EandM
Siemens STEP 2000 CourseAC MotorsIt's easy to get in STEP!Download any course.Hint: Make sure you download all parts for each course and the test answer form.Complete each chapter and its review sectionPrint the test answer form, take the final exam and fill in the form.Hint: The final exam is always at the end of the last part.Send your test answer form to EandM for grading. If you achieve a score of 70% or better, we'llsend you a certificate of completion! If you have any questions, contact EandM Training at866.693.2636 or fax 707.473.3190 or training@eandm.com.Need more information? Contact EandM at866.693.2636or fax 707.473.3190or sales@eandm.comfor product information, quotes,classroom training courses and more.STEP 2000 Courses distributed bywww.eandm.com
Table of ContentsIntroduction .2AC Motors .4Force and Motion .6AC Motor Construction . 14Magnetism .20Electromagnetism .22Developing a Rotating Magnetic Field .28Rotor Rotation.34Motor Specifications .39NEMA Motor Characteristics .43Derating Factors .51AC Motors and AC Drives .53Matching AC Motors to the Load .58Enclosures .63Mounting .67Siemens Motors . 74Above NEMA Motors .79Review Answers .84Final Exam .851
IntroductionWelcome to another course in the STEP series, SiemensTechnical Education Program, designed to prepare ourdistributors to sell Siemens Energy & Automation productsmore effectively. This course covers Basics of AC Motors andrelated products.Upon completion of Basics of AC Motors you should be ableto:2 Explain the concepts of force, inertia, speed, and torque Explain the difference between work and power Describe the construction of a squirrel cage AC motor Describe the operation of a rotating magnetic field Calculate synchronous speed, slip, and rotor speed Plot starting torque, accelerating torque, breakdowntorque, and full-load torque on a NEMA torque curve Apply derating factors as required by an application Describe the relationship between V/Hz, torque, andhorsepower Match an AC motor to an application and its load Identify NEMA enclosures and mounting configurations Describe Siemens Medallion , PE-21 Plus , verticalpump, and IEC motors Describe torque characteristics and enclosures of Siemensabove NEMA motors
This knowledge will help you better understand customerapplications. In addition, you will be better able to describeproducts to customers and determine important differencesbetween products. You should complete Basics of Electricitybefore attempting Basics of AC Motors. An understandingof many of the concepts covered in Basics of Electricityis required for Basic of AC Motors. You may also want tocomplete Basics of Control Components which discussesthe application of control devices for start, stop, and thermalprotection of AC motors.If you are an employee of a Siemens Energy & Automationauthorized distributor, fill out the final exam tear-out card andmail in the card. We will mail you a certificate of completion ifyou score a passing grade. Good luck with your efforts.Medallion and PE-21 Plus are trademarks of Siemens Energy &Automation, Inc.National Electrical Code and NEC are registered trademarksof the National Fire Protection Association, Quincy, MA 02269.Portions of the National Electrical Code are reprinted withpermission from NFPA 70-2002, National Electrical CodeCopyright, 2001, National Fire Protection Association, Quincy,MA 02269. This reprinted material is not the complete andofficial position of the National Fire Protection Association onthe referenced subject which is represented by the standard inits entirety.Underwriters Laboratories Inc. is a registered trademark ofUnderwriters Laboratories Inc., Northbrook, IL 60062. Theabbreviation “UL” shall be understood to mean UnderwritersLaboratories Inc.National Electrical Manufacturers Association is locatedat 2101 L. Street, N.W., Washington, D.C. 20037. Theabbreviation “NEMA” is understood to mean National ElectricalManufacturers Association.3
AC MotorsAC motors are used worldwide in many residential, commercial,industrial, and utility applications. Motors transform electricalenergy into mechanical energy. An AC motor may be part of apump or fan, or connected to some other form of mechanicalequipment such as a winder, conveyor, or mixer. AC motorsare found on a variety of applications from those that require asingle motor to applications requiring several motors. Siemensmanufactures a wide variety of motors for various applications.The material presented in this course will help in selection of amotor for a specific application.4
NEMAThroughout this course reference is made to the NationalElectrical Manufacturers Association (NEMA). NEMA setsstandards for a wide range of electrical products, includingmotors. NEMA is primarily associated with motors used inNorth America. The standards developed represent generalindustry practices and are supported by manufacturers ofelectrical equipment. These standards can be found in NEMAStandard Publication No. MG 1. Some large AC motors may notfall under NEMA standards. These motors are built to meet therequirements of a specific application. These are referred to asabove NEMA motors.IECThe International Electrotechnical Commission (IEC) is anotherorganization responsible for motor standards. IEC standardsare a group of recommended electrical practices developedby committees from participating IEC countries. Thesestandards are different than NEMA standards. IEC standardsare associated with motors used in many countries, includingmotors used in North America. These standards can be found inIEC 34-1-16. Motors which meet or exceed these standards arereferred to as IEC motors.5
Force and MotionBefore discussing AC motors it is necessary to understandsome of the basic terminology associated with motor operation.Many of these terms are familiar to us in some other context.Later in the course we will see how these terms apply to ACmotors.ForceIn simple terms, a force is a push or a pull. Force may becaused by electromagnetism, gravity, or a combination ofphysical means.Net forceNet force is the vector sum of all forces that act on an object,including friction and gravity. When forces are applied in thesame direction they are added. For example, if two 10 poundforces are applied in the same direction the net force would be20 pounds.If 10 pounds of force is applied in one direction and 5 poundsof force is applied in the opposite direction, the net force wouldbe 5 pounds and the object would move in the direction of thegreater force.6
If 10 pounds of force is applied equally in both directions, thenet force would be zero and the object would not move.TorqueTorque is a twisting or turning force that causes an object torotate. For example, a force applied to the end of a lever causesa turning effect or torque at the pivot point.Torque (τ) is the product of force and radius (lever distance).τ Force x RadiusIn the English system torque is measured in pound-feet (lb-ft) orpound-inches (lb-in). For example, if 10 lbs of force is applied toa lever 1 foot long the resulting torque would be 10 lb-ft.An increase in force or radius would result in a correspondingincrease in torque. Increasing the radius to two feet, forexample, results in 20 lb-ft of torque.7
SpeedAn object in motion travels a distance in a given time. Speed isthe ratio of the distance traveled and the time it takes to travelthe distance.Linear SpeedThe linear speed of an object determines how long it takes theobject to get from point A to point B. Linear speed is usuallyexpressed in a form that combines units of distance divided byunits of time such as meters per second (m/s). For example,if the distance between point A and point B were 10 meters,and it took 2 seconds to travel the distance, the speed wouldbe 5 m/s.Angular (Rotational) SpeedThe angular speed of a rotating object determines how longit takes a given point on the object to make one completerevolution from its starting point. Angular speed is oftenexpressed in revolutions per minute (RPM). An object thatmakes ten complete revolutions in one minute, for example,has a speed of 10 RPM.8
AccelerationAn object can change speed. An increase in speed is calledacceleration. Acceleration occurs only when there is a changein the force acting upon the object. An object can also changefrom a higher to a lower speed. This is known as deceleration(negative acceleration). A rotating object, for example, canaccelerate from 10 RPM to 20 RPM, or decelerate from 20RPM to 10 RPM.InertiaMechanical systems are subject to the law of inertia. The lawof inertia states that an object will tend to remain in its currentstate of rest or motion unless acted upon by an external force.This property of resistance to acceleration/deceleration isreferred to as the moment of inertia. The English system of2measurement is pound-feet squared (lb-ft ).If we look at a continuous roll of paper, for example, we knowthat when the roll is stopped it would take a certain amountof force to overcome the inertia of the roll to get it rolling. Theforce required to overcome this inertia can come from a sourceof energy such as a motor. Once rolling, the paper will continueunwinding until another force acts on it to bring it to a stop.9
FrictionAny system in motion has losses that drain energy from thesystem. The law of inertia is still valid, however, because thesystem will remain in motion at constant speed if energy isadded to the system to compensate for the losses. In theprevious illustration, for example, these losses include: WorkFriction applied to motor and driven equipment bearingsWind losses in the motor and driven equipmentFriction between material on winder and rollersWhenever a force of any kind causes motion, work isaccomplished. For example, work is accomplished when anobject on a conveyor is moved from one point to another.Work is generally expressed in foot-pounds and is defined bythe product of the net force (F) applied and the distance (d)moved. If twice the force is applied, twice the work is done. Ifan object moves twice the distance, twice the work is done.W FxdPower10Power is the rate of doing work, or work divided by time.
In other words, power is the amount of work it takes to movethe package from one point to another point, divided by thetime.HorsepowerPower can be expressed in foot-pounds per second, but isoften expressed in horsepower (HP). This unit was defined inthe 18th century by James Watt. Watt sold steam engines andwas asked how many horses one steam engine would replace.He had horses walk around a wheel that would lift a weight.He found that a horse would average about 550 foot-pounds ofwork per second. One horsepower is equivalent to 550 footpounds per second or 33,000 foot-pounds per minute.The following formula can be used to calculate horsepowerwhen torque (in lb-feet) and speed are known. An increase oftorque, speed, or both will cause an increase in horsepower.11
Horsepower and KilowattsAC motors manufactured in the United States are generallyrated in horsepower (HP). Equipment manufactured in Europe isgenerally rated in kilowatts (KW). Horsepower can be convertedto kilowatts with the following formula:KW .746 x HPFor example, a 25 HP motor is equivalent to 18.65 KW.18.65 KW .746 x 25 HPKilowatts can be converted to horsepower with the followingformula:HP 1.341 x KWThe power formula for a single-phase system is:The power formula for three-phase power is:12
Review 11.A is a push or a pull.2.An object has 20 pounds of force applied in onedirection and 5 pounds of force applied in the oppositedirection. The net force is pounds.3.A twisting or turning force that causes an object torotate is known as .4.If 40 pounds of force were applied to a lever 2 feet long,the torque would be lb-ft.5.The law of states that an object will tendto remain in its current state of rest or motion unlessacted upon by an external force.6.is the ratio of distance traveled and time.7.The speed of a rotating object is generally given inper .8.occurs when there is an increase in anobject’s speed.13
AC Motor ConstructionAC induction motors are commonly used in industrialapplications. The following motor discussion will center aroundthree-phase, 460 VAC, asynchronous, induction motors. Anasynchronous motor is a type of motor where the speed of therotor is less than the speed of the rotating magnetic field. Thistype of motor is illustrated below. The three basic parts of an ACmotor are the rotor, stator, and enclosure.14
Stator ConstructionThe stator and the rotor are electrical circuits that perform aselectromagnets. The stator is the stationary electrical part of themotor. The stator core of a NEMA motor is made up of severalhundred thin laminations.Stator WindingsStator laminations are stacked together forming a hollowcylinder. Coils of insulated wire are inserted into slots of thestator core.15
Each grouping of coils, together with the steel core it surrounds,form an electromagnet. Electromagnetism is the principlebehind motor operation. The stator windings are connecteddirectly to the power source.Rotor Construction16The rotor is the rotating part of the electromagnetic circuit.The most common type of rotor is the “squirrel cage” rotor.Other types of rotor construction will be mentioned later in thecourse. The construction of the squirrel cage rotor is reminiscentof rotating exercise wheels found in cages of pet rodents.
The rotor consists of a stack of steel laminations with evenlyspaced conductor bars around the circumference.The laminations are stacked together to form a rotor core.Aluminum is die cast in the slots of the rotor core to form aseries of conductors around the perimeter of the rotor. Theconductor bars are mechanically and electrically connected withend rings. The rotor core mounts on a steel shaft to form a rotorassembly.17
EnclosureThe enclosure consists of a frame (or yoke) and two endbrackets (or bearing housings). The stator is mounted insidethe frame. The rotor fits inside the stator with a slight airgap separating it from the stator. There is no direct physicalconnection between the rotor and the stator.The enclosure also protects the electrical and operating parts ofthe motor from harmful effects of the environment in which themotor operates. Bearings, mounted on the shaft, support therotor and allow it to turn. A fan, also mounted on the shaft, isused on the motor shown below for cooling.18
Review 21.Identify the following components from the illustration:A.B.C.2.The and the are two partsof an electrical circuit that form an electromagnet.3.The is the stationary electrical part of anAC motor.4.The is the rotating electrical part of an ACmotor.5.The rotor is the mostcommon type of rotor used in AC motors.19
MagnetismThe principles of magnetism play an important role in theoperation of an AC motor. All magnets have two characteristics.They attract and hold metal objects like steel and iron. If freeto move, like the compass needle, the magnet will assumeroughly a north-south position.SNMagnetic Lines of Flux20We know that a magnet attracts an iron or steel object by aninvisible force. The magnet’s invisible force is called lines of flux.These lines of flux make up an invisible magnetic field. Everymagnet has two poles, one north pole and one south pole.Invisible magnetic lines of flux leave the north pole and enterthe south pole. While the lines of flux are invisible, the effectsof magnetic fields can be made visible. When a sheet of paperis placed on a magnet and iron filings loosely scattered over it,the filings will arrange themselves along the invisible lines offlux.
By drawing lines the way the iron filings have arrangedthemselves, the following illustration is obtained. Magnetic linesof flux always form closed loops, leaving the north pole andentering the south pole. They return to the north pole throughthe magnet.Unlike Poles AttractThe polarity of the magnetic field affects the interactionbetween magnets. For example, when the opposite poles oftwo magnets are brought within range of each other the linesof flux combine and tend to pull or attract the magnets.Like Poles RepelWhen poles of like polarity of two magnets are brought withinrange of each other the lines of flux produce a force thattends to push or repel the magnets. For this reason it is saidthat unlike poles attract and like poles repel. The attractingand repelling action of the magnetic fields is important in theoperation of AC motors.21
ElectromagnetismWhen current flows through a conductor a magnetic field isproduced around the conductor. The magnetic field is made upof lines of flux, just like a natural magnet. The size and strengthof the magnetic field will increase and decrease as the currentflow strength increases and decreases.22
Left-Hand Rule forConductorsA definite relationship exists between the direction of currentflow and the direction of the magnetic field. The left-hand rulefor conductors demonstrates this relationship. If a currentcarrying conductor is grasped with the left hand with the thumbpointing in the direction of electron flow, the fingers will point inthe direction of the magnetic lines of flux.In the following illustration it can be seen that when theelectron flow is away from the viewer (indicated by the plussign) the lines of flux flow in a counterclockwise directionaround the conductor. When the electron flow reverses andcurrent flow is towards the viewer (indicated by the dot) thelines of flux reverse direction and flow in a clockwise direction.23
ElectromagnetAn electromagnet can be made by winding the conductor intoa coil and applying a DC voltage. The lines of flux, formed bycurrent flow through the conductor, combine to produce a largerand stronger magnetic field. The center of the coil is known asthe core. In this simple electromagnet the core is air.Adding an Iron CoreIron is a better conductor of flux than air. The air core of anelectromagnet can be replaced by a piece of soft iron. When apiece of iron is placed in the center of the coil more lines of fluxcan flow and the magnetic field is strengthened.Number of TurnsThe strength of the magnetic field in the DC electromagnet canbe increased by increasing the number of turns in the coil. Thegreater the number of turns the stronger the magnetic field.24
Changing PolarityThe magnetic field of an electromagnet has the samecharacteristics as a natural magnet, including a north and southpole.
Siemens STEP 2000 Course AC Motors It's easy to get in STEP! Download any course. Hint: Make sure you download all parts for each course and the test answer form. Complete each chapter and its review section Print the test answer form, take the final exam and fill in the form. Hint: The final exam is always at the end of the last part.
send you a certificate of completion! If you have any questions, contact EandM Training at 866.693.2636 or fax 707.473.3190 or training@eandm.com. Need more information? Contact EandM at 866.693.2636 or fax 707.473.3190 or sales@eandm.com for product information, quotes, classroom training courses and more. STEP 2000 Courses distributed by
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