ac motors

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Table of Contents

Introduction ..............................................................................2

AC Motors ................................................................................4

Force and Motion .....................................................................6

AC Motor Construction ...........................................................12

Magnetism ............................................................................. 17

Electromagnetism ..................................................................19

Developing a Rotating Magnetic Field ....................................24

Rotor Rotation .........................................................................29

Motor Specifications ...............................................................34

NEMA Motor Characteristics ..................................................37

Derating Factors .....................................................................43

AC Motors and AC Drives .......................................................45

Matching Motors to the Load .................................................49

Motor Enclosures ...................................................................53

Mounting ................................................................................56

Siemens AC Induction Motors ................................................61

Review Answers.....................................................................7

Final Exam .............................................................................. 74

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Introduction

Welcome to another course in the STEP series, SiemensTechnical Education Program, designed to prepare ourdistributors to sell Siemens Industry, Inc. products moreeffectively. This course covers Basics of AC Motorsand relateproducts.

Upon completion of Basics of AC Motorsyou should be ableto:

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, breakdown

torque, and full-load torque on a NEMA torque curve

Apply derating factors as required by an application Describe the relationship between V/Hz, torque, and

horsepower

Match an AC motor to an application and its load Identify NEMA enclosures and mounting configurations Describe Siemens NEMA, IEC, and above 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 Electricityisrequired for this course.

After you have completed this course, if you wish to determinehow well you have retained the information covered, you cancomplete a final exam online as described later in this course. you pass the exam, you will be given the opportunity to print acertificate of completion.

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Siemens is a trademark of Siemens AG. Product namesmentioned may be trademarks or registered trademarks of therespective companies. Specifications subject to change withounotice.

NEMA is a registered trademark and service mark of theNational Electrical Manufacturers Association, Rosslyn, VA

22209.

Underwriters Laboratories Inc. and UL are registeredtrademarks of Underwriters Laboratories Inc., Northbrook, IL60062-2096.

Other trademarks are the property of their respective owners.

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AC Motors

AC motorsare used worldwide in many applications totransform electrical energy into mechanical energy. There aremany types of AC motors, but this course focuses on three-phase AC induction motors, the most common type of motoused in industrial applications.

An AC motor of this type may be part of a pump or fan orconnected to some other form of mechanical equipment suchas a winder, conveyor, or mixer. Siemens manufactures a widevariety of AC motors. In addition to providing basic information

about AC motors in general, this course also includes anoverview of Siemens AC motors.

Winder

Pump

Conveyor

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NEMA Motors Throughout this course, reference is made to the NationalElectrical Manufacturers Association (NEMA). NEMAdevelops standards for a wide range of electrical products,including AC motors. For example, NEMA Standard PublicationMG 1 covers NEMA frame size AC motors, commonly referredto as NEMA motors.

Above NEMA Motors In addition to manufacturing NEMA motors, Siemens alsomanufactures motors larger than the largest NEMA framesize. These motors are built to meet specific applicationrequirements and are commonly referred to asabove NEMAmotors.

IEC Motors Siemens also manufactures motors to InternationalElectrotechnical Commission (IEC)standards. IEC is anotheorganization responsible for electrical standards. IEC standardsperform the same function as NEMA standards, but differ

in many respects. In many countries, electrical equipmentis commonly designed to comply with IEC standards. In theUnited States, although IEC motors are sometimes used,NEMA motors are more common. Keep in mind, however,that many U.S.-based companies build products for export tocountries that follow IEC standards.

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Force and Motion

Before discussing AC motors it is necessary to understandsome of the basic terminology associated with motor operatioMany of these terms are familiar to us in some other context.Later in the course we will see how these terms apply to ACmotors.

Force In simple terms, a forceis a push or a pull. Force may becaused by electromagnetism, gravity, or a combination ofphysical means.

Net Force Net forceis 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.

=10 LB 20 LB10 LB

If 10 pounds of force is applied in one direction and 5 poundsof force is applied in the opposite direction, the net force woulbe 5 pounds and the object would move in the direction of thegreater force.

=5 LB10 LB 5 LB

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If 10 pounds of force is applied equally in both directions, thenet force would be zero and the object would not move.

= 010 LB10 LB

Torque Torqueis a twisting or turning force that causes an object torotate. For example, a force applied to the end of a lever causea turning effect or torque at the pivot point.

Torque () is the product of force and radius (lever distance).

= Force x Radius

In the English system of measurements, torque is measured inpound-feet (lb-ft) or pound-inches (lb-in). For example, if 10 lbsof force is applied to a lever 1 foot long, the resulting torque is10 lb-ft.

1 foot

Torque (t) = 10 lb-ft

Force = 10 pounds

An increase in force or radius results in a correspondingincrease in torque. Increasing the radius to two feet, forexample, results in 20 lb-ft of torque.

2 feet

Torque (t) = 20 lb-ft

Force = 10 pounds

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Speed An object in motion takes time to travel any distance. Speedisthe ratio of the distance traveled and the time it takes to travelthe distance.

Linear Speed Linear speedis the rate at which an object travels a specified

distance. Linear speed is expressed in units of distance dividedby units of time, for example, miles per hour or meters persecond (m/s). Therefore, if it take 2 seconds to travel 40 meterthe speed is 20 m/s.

Linear Motion

Angular (Rotational) Speed The angular speedof a rotating object determines how longit takes for an object to rotate a specified angular distance.Angular speed is often expressed in revolutions per minute(RPM). For example, an object that makes ten completerevolutions in one minute, has a speed of 10 RPM.

Axis of RotationDirection of

Rotation

Rotional Motion

Acceleration An 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.

10 RPM 20 RPM

Acceleration

20 RPM 10 RPM

Deceleration

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Inertia Mechanical 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 unit omeasurement for inertia is pound-feet squared (lb-ft

2).

For example, consider a machine that unwinds a large roll ofpaper. If the roll is not moving, it takes a force to overcomeinertia and start the roll in motion. Once moving, it takes a forcin the reverse direction to bring the roll to a stop.

Any 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.

Friction Frictionoccurs when objects contact one another. As we allknow, when we try to move one object across the surfaceof another object, friction increases the force we must apply.Friction is one of the most significant causes of energy loss in

machine.

Work Whenever a force causes motion, workis accomplished. Workcan be calculated simply by multiplying the force that causesthe motion times the distance the force is applied.

Work = Force x Distance

Since work is the product of force times the distance applied,work can be expressed in any compound unit of force timesdistance. For example, in physics, work is commonly expresse

in joules. 1 joule is equal to 1 newton-meter, a force of 1newton for a distance of 1 meter. In the English system ofmeasurements, work is often expressed in foot-pounds (ft-lb),where 1 ft-lb equals 1 foot times 1 pound.

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Power Another often used quantity is power. Power is the rate ofdoing work or the amount of work done in a period of time.

Horsepower Power can be expressed in foot-pounds per second, but isoften expressed in horsepower. This unit was defined in the18th century by James Watt. Watt sold steam engines and wasasked how many horses one steam engine would replace. Hehad horses walk around a wheel that would lift a weight. Hefound that a horse would average about 550 foot-pounds ofwork per second. Therefore, one horsepower is equal to 550foot-pounds per second or 33,000 foot-pounds per minute.

When applying the concept of horsepower to motors, it isuseful to determine the amount of horsepower for a givenamount of torque and speed. When torque is expressed in lb-fand speed is expressed in RPM, the following formula can beused to calculate horsepower (HP). Note that an increase intorque, speed, or both increases horsepower.

power in HP =Torque in lb-ft x Speed in RPM

5252

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Horsepower and Kilowatts AC motors manufactured in the United States are generallyrated in horsepower, but motors manufactured in many othercountries are generally rated in kilowatts(kW). Fortunately it ieasy to convert between these units.

power in kW = 0.746 x power in HP

For example, a a motor rated for 25 HP motor is equivalent to amotor rated for 18.65 kW.

0.746 x 25 HP = 18.65 kW

Kilowatts can be converted to horsepower with the followingformula.

power in HP = 1.34 x power in kW

Review 1

1. If 20 pounds of force is applied in one direction and 5pounds of force is applied in the opposite direction, thenet force is ___ pounds.

2. ________ is a twisting or turning force.

3. If 40 pounds of force is applied at the end of a lever2 feet long, the torque is ___ lb-ft.

4. The law of ________ states that an object will tend

to remain in its current state of rest or motion unlessacted upon by an external force.

5. ________ is equal to the distance traveled divided bythe elapsed time.

6. The speed of a rotating object is often expressed in________.

7. An increase in an objects speed is called ________.

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AC Motor Construction

Three-phase AC induction motorsare commonly used inindustrial applications. This type of motor has three main partsrotor, stator, and enclosure. The stator and rotor do the workand the enclosure protects the stator and rotor.

Enclosure

Stator

Rotor

Stator Core The stator is the stationary part of the motors electromagneticcircuit. The stator core is made up of many thin metal sheets,called laminations. Laminations are used to reduce energyloses that would result if a solid core were used.

Stator Lamination

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Stator Windings Stator laminations are stacked together forming a hollowcylinder. Coils of insulated wire are inserted into slots of thestator core.

Stator Windings Partially Completed

When the assembled motor is in operation, the stator windingare connected directly to the power source. Each grouping ofcoils, together with the steel core it surrounds, becomes anelectromagnet when current is applied. Electromagnetismisthe basic principle behind motor operation.

Stator Windings Completed

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Rotor Construction The rotor is the rotating part of the motors electromagneticcircuit. The most common type of rotor used in a three-phaseinduction motor is a squirrel cage rotor. Other types of rotorconstruction is discussed later in the course. The squirrel cagerotor is so called because its construction is reminiscent of therotating exercise wheels found in some pet cages.

Rotor

A squirrel cage rotor core is made by stacking thin steellaminations to form a cylinder.

Rotor Lamination

Rather than using coils of wire as conductors, conductor bars

are die cast into the slots evenly spaced around the cylinder.Most squirrel cage rotors are made by die casting aluminum toform the conductor bars. Siemens also makes motors with diecast copper rotor conductors. These motor exceed NEMAPremium efficiency standards.

After die casting, rotor conductor bars are mechanically andelectrically connected with end rings. The rotor is then pressedonto a steel shaft to form a rotor assembly.

Cutaway View of Rotor

Conductor BarEnd Ring

Shaft

Steel Laminations

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Enclosure The 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.

FrameRotor

Stator

Air Gap

Partially Assembled Motor

The enclosure protects the internal parts of the motor fromwater and other environmental elements. The degree ofprotection depends upon the type of enclosure. Enclosuretypes are discussed later in this course.

Bearings, mounted on the shaft, support the rotor and allowit to turn. Some motors, like the one shown in the followingillustration, use a fan, also mounted on the rotor shaft, to coolthe motor when the shaft is rotating.

Bearing

End Bracket

(Bearing Housing)

Rotor

Stator Cooling Fan

Frame (Yoke)

Bearing

End Bracket

(Bearing Housing)

Cutaway View of Motor

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Review 2

1. Identify the following components from the illustration:

A. ________ B. ________ C. ________

2. The ________ is the stationary part of an AC motorselectromagnetic circuit.

3. The ________ is the rotating electrical part of an ACmotor.

4. The ________ rotor is the most common type of rotorused in three-phase AC motors.

5. The ________ protects the internal parts of the motorfrom water and other environmental elements.

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Magnetism

The principles of magnetismplay an important role in theoperation of an AC motor. Therefore, in order to understandmotors, you must understand magnets.

To begin with, all magnets have two characteristics. They attraciron and steel objects, and they interact with other magnets.This later fact is illustrated by the way a compass needle alignsitself with the Earths magnetic field.

N

S

Magnetic Lines of Flux The force that attracts an iron or steel object has continuous

magnetic field lines, called lines of flux, that run through themagnet, exit the north pole, and return through the southpole. Although these lines of flux are invisible, the effects ofmagnetic fields can be made visible. For example, when asheet of paper is placed on a magnet and iron filings are looselscattered over the paper, the filings arrange themselves alongthe invisible lines of flux.

Magnet

Iron Filings on Paper

Magnetic Lines of Flux

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Unlike Poles Attract The polaritiesof magnetic fields affect the interaction betweemagnets. For example, when the opposite poles of twomagnets are brought within range of each other, the lines offlux combine and pull the magnets together.

Like Poles Repel However, when like poles of two magnets are brought withinrange of each other, their lines of flux push the magnetsapart. In summary, unlike poles attractand like poles repel.The attracting and repelling action of the magnetic fields is

essential to the operation of AC motors, but AC motors useelectromagnetism.

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Electromagnetism

When current flows through a conductor, it produces amagnetic field around the conductor. The strength of themagnetic field is proportional to the amount of current.

Current produces a magnetic field

An increased current produces a stronger magnetic field

Left-Hand Rule for The left-hand rule for conductorsdemonstrates theConductors relationship between the flow of electrons and the direction

of the magnetic field created by this current. If a current-carrying conductor is grasped with the left hand with the thumpointing in the direction of electron flow, the fingers point in thdirection of the magnetic lines of flux.

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The following illustration shows that, when the electron flowis away from the viewer (as indicated by the plus sign), thelines of flux flow in a counterclockwise direction around theconductor. When the electron flow reverses and current flowis towards the viewer (as indicated by the dot), the lines of fluxflow in a clockwise direction.

Electron Flow Away From You

Causes Counterclockwise Magnetic Flux

Electron Flow Towards You

Causes Clockwise Magnetic Flux

Electromagnet An electromagnetcan be made by winding a conductor intoa coil and applying a DC voltage. The lines of flux, formed bycurrent flow through the conductor, combine to produce a largand stronger magnetic field. The center of the coil is known as

the core. This simple electromagnet has an air core.

DC Voltage

Air Core

Adding an Iron Core Iron conducts magnetic flux more easily than air. When an

insulated conductor is wound around an iron core, a strongermagnetic field is produced for the same level of current.

Iron Core

DC Voltage

Number of Turns The strength of the magnetic field created by theelectromagnet can be increased further by increasing thenumber of turnsin the coil. The greater the number of turns thstronger the magnetic field for the same level of current.

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DC Voltage

5 Turns

DC Voltage

10 Turns

Changing Polarity The magnetic field of an electromagnet has the samecharacteristics as a natural magnet, including a north and southpole. However, when the direction of current flow throughthe electromagnet changes, the polarity of the electromagnetchanges.

The polarity of an electromagnet connected to an ACsource changes at the frequencyof the AC source. This isdemonstrated in the following illustration.

N

S

N

S

N

S

N

S

N

S

N

S

1

2

3

4 5

6

7

8

10

At time 1, there is no current flow, and no magnetic field isproduced. At time 2, current is flowing in a positive direction,and a magnetic field builds up around the electromagnet. Notethat the south pole is on the top and the north pole is on thebottom. At time 3, current flow is at its peak positive value, andthe strength of the electromagnetic field has also peaked. Attime 4, current flow decreases, and the magnetic field begins tcollapse.

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At time 5, no current is flowing and no magnetic field isproduced. At time 6, current is increasing in the negativedirection. Note that the polarity of the electromagnetic fieldhas changed. The north pole is now on the top, and the southpole is on the bottom. The negative half of the cycle continuesthrough times 7 and 8, returning to zero at time 9. For a 60 HzAC power supply, this process repeats 60 times a second.

Induced Voltage In the previous examples, the coil was directly connected toa power supply. However, a voltage can be inducedacross aconductor by merely moving it through a magnetic field. Thissame effect is caused when a stationary conductor encountersa changing magnetic field. This electrical principle is critical tothe operation of AC induction motors.

In the following illustration, an electromagnet is connected to aAC power source. Another electromagnet is placed above it. Thsecond electromagnet is in a separate circuit and there is no

physical connection between the two circuits.

Time 1 Time 2 Time 3

Ammeter AmmeterAmmeter

This illustration shows the build up of magnetic flux during thefirst quarter of the AC waveform. At time 1, voltage and currenare zero in both circuits. At time 2, voltage and current areincreasing in the bottom circuit. As magnetic field builds up inthe bottom electromagnet, lines of flux from its magnetic fieldcut across the top electromagnet and induce a voltage acrossthe electromagnet. This causes current to flow through theammeter. At time 3, current flow has reached its peak in bothcircuits. As in the previous example, the magnetic field aroundeach coil expands and collapses in each half cycle, and reversepolarity from one half cycle to another.

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Electromagnetic Attraction Note, however, that the polarity of the magnetic field induced the top electromagnet is opposite the polarity of the magneticfield in the bottom electromagnet. Because opposite polesattract, the two electromagnets attract each other wheneverflux has built up. If it were possible to move the bottomelectromagnet, and the magnetic field was strong enough, thetop electromagnet would be pulled along with it.

Original Position New Position

Review 3

1. Magnetic lines of flux leave the _______ pole of amagnet and enter the _______ pole.

2. In the following illustration, which magnets will attracteach other and which magnets will repel each other?

3. A _______ is produced around a conductor whencurrent is flowing through it.

4. Which of the following will increase the strength of themagnetic field for an electromagnet?

A. Increase the current flow B. Increase the number of turns in the coil C. Add an iron core to a coil D. All the above

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Developing a Rotating Magnetic Field

The principles of electromagnetism explain the shaft rotation oan AC motor. Recall that the stator of an AC motor is a hollowcylinder in which coils of insulated wire are inserted.

Stator Coil Arrangement The following diagram shows the electrical configuration ofstator windings. In this example, six windings are used, two foeach of the three phases. The coils are wound around the softiron core material of the stator. When current is applied, eachwinding becomes an electromagnet, with the two windings foeach phase operating as the opposite ends of one magnet.

In other words, the coils for each phase are wound in such away that, when current is flowing, one winding is a north poleand the other is a south pole. For example, when A1 is a northpole, A2 is a south pole and, when current reverses direction,the polarities of the windings also reverse.

A1

A2

B2

B1

C2

C1

N

S

Iron CoreMotor Windings

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Stator Power Source The stator is connected to a three-phase AC power source. Thefollowing illustration shows windings A1 and A2 connectedto phase A of the power supply. When the connections arecompleted, B1 and B2 will be connected to phase B, and C1and C2 will be connected to phase C.

A1

A2

B2

B1

C2

C1

N

S

To Phase A

To Phase A

Phase A Phase CPhase B

0

+

-

As the following illustration shows, coils A1, B1, and C1 are120 apart. Note that windings A2, B2, and C2 also are 120apart. This corresponds to the 120 separation between eachelectrical phase. Because each phase winding has two poles,this is called a two-pole stator.

A1

A2

C2B2

B1C1

2-Pole Stator Winding

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When AC voltage is applied to the stator, the magnetic fielddeveloped in a set of phase coils depends on the directionof current flow. Refer to the following chart as you read theexplanation of how a rotating magnetic field is developed. Thischart assumes that a positive current flow in the A1, B1 or C1windings results in a north pole.

Start In the following illustration, a start time has been selectedduring which phase A has no current flow and its associated

coils have no magnetic field. Phase B has current flow in thenegative direction and phase C has current flow in the positivedirection. Based on the previous chart, B1 and C2 are southpoles and B2 and C1 are north poles. Magnetic lines of fluxleave the B2 north pole and enter the nearest south pole, C2.Magnetic lines of flux also leave the C1 north pole and enter thnearest south pole, B1. The vector sum of the magnetic fields iindicated by the arrow.

Resultant Magnetic Field

Magnetic Lines of Flux

Current Flow in the Positive Direction

Current Flow at Zero

Current Flow in the Negative Direction

Start

C

A

B

A1

B2

C1

A2

B1

C2N S

N S

Time 1 The following chart shows the progress of the magnetic fieldvector as each phase has advanced 60. Note that at time 1phase C has no current flow and no magnetic field is developein C1 and C2. Phase A has current flow in the positive directionand phase B has current flow in the negative direction.

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As the previous chart shows, windings A1 and B2 are northpoles and windings A2 and B1 are south poles. The resultantmagnetic field vector has rotated 60 in the clockwise direction



Current Flow in the Negative DirectionStart

C

A

B

A1

B2

C1

A2

B1

C2N

S

N

S 60o

60o

1

A1

B2

C1

A2

B1

C2N S

N S

Time 2 At time 2, phase B has no current flow and windings B1 andB2 have no magnetic field. Current in phase A is flowing inthe positive direction, but phase C current is now flowing inthe negative direction. The resultant magnetic field vector hasrotated another 60.



Current Flow in the Negative Direction

Start

C

A

B

A1

B2

A2

B1

C2N

S

N

S

60o

1

A1

B2

C1

A2

B1

C2S

N S

120o

2

60o

C1

A1

B2

C1

A2

B1

C2N

N

SS

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360 Rotation At the end of six such time intervals, the magnetic field willhave rotated one full revolution or 360. This process repeats 6times a second for a 60 Hz power source.

Synchronous Speed The speed of the rotating magnetic field is referred to as thesynchronous speed (NS)of the motor. Synchronous speed isequal to 120 times the frequency (F), divided by the numberof motor poles (P).

The synchronous speed for a two-pole motor operated at 60 Hfor example, is 3600 RPM.

Synchronous speed decreases as the number of polesincreases. The following table shows the synchronous speed a60 Hz for several different pole numbers.

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Rotor Rotation

Permanent Magnet To see how a rotor works, a magnet mounted on a shaft canbe substituted for the squirrel cage rotor. When the statorwindings are energized, a rotating magnetic field is establishedThe magnet has its own magnetic field that interacts withthe rotating magnetic field of the stator. The north pole of therotating magnetic field attracts the south pole of the magnet,and the south pole of the rotating magnetic field attracts thenorth pole of the magnet. As the magnetic field rotates, it pullsthe magnet along. AC motors that use a permanent magnetfor a rotor are referred to as permanent magnet synchronous

motors. The term synchronousmeans that the rotors rotationis synchronized with the magnetic field, and the rotors speed the same as the motors synchronous speed.

Induced Voltage Instead of a permanent magnet rotor, a squirrel cage inductionElectromagnet motor induces a current in its rotor, creating an electromagnet.

As the following illustration shows, when current is flowing ina stator winding, the electromagnetic field created cuts acrossthe nearest rotor bars.

A1

A2

C2B2

B1C1

Rotor Conductor Bar

Stator

Rotor

Magnetic Field of Coil A1

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When a conductor, such as a rotor bar, passes through amagnetic field, a voltage (emf) is induced in the conductor.The induced voltage causes current flow in the conductor. Ina squirrel cage rotor, current flows through the rotor bars andaround the end ring and produces a magnetic field around eachrotor bar.

Because the stator windings are connected to an AC source,the current induced in the rotor bars continuously changesand the squirrel cage rotor becomes an electromagnet withalternating north and south poles.

The following illustration shows an instant when winding A1 isa north pole and its field strength is increasing. The expandingfield cuts across an adjacent rotor bar, inducing a voltage. Theresultant current flow in one rotor bar produces a south pole.This causes the motor to rotate towards the A1 winding.

At any given point in time, the magnetic fields for the stator

windings are exerting forces of attraction and repulsion againstthe various rotor bars. This causes the rotor to rotate, but notexactly at the motors synchronous speed.

A1

A2

C2B2

B1C1

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Slip For a three-phase AC induction motor, the rotating magneticfield must rotate faster than the rotor to induce current in therotor. When power is first applied to the motor with the rotorstopped, this difference in speed is at its maximum and a largeamount of current is induced in the rotor.

After the motor has been running long enough to get up to

operating speed, the difference between the synchronousspeed of the rotating magnetic field and the rotor speedis much smaller. This speed difference is called slip. Slip isnecessary to produce torque. Slip is also dependent on load. Aincrease in load causes the rotor to slow down, increasing slipA decrease in load causes the rotor to speed up, decreasingslip. Slip is expressed as a percentage and can be calculatedusing the following formula.

% Slip = x 100N

S- N

R

NS

For example, a four-pole motor operated at 60 Hz has asynchronous speed (NS)of 1800 RPM. If its rotor speed (NRat full load is 1775 RPM, then its full load slip is 1.4%.

% Slip =

% Slip = 1.4%

1800 - 17751800

x 100

Wound Rotor Motor The discussion to this point has been centered on the morecommon squirrel cage rotor. Another type of three-phaseinduction motor is the wound rotor motor. A major differencebetween the wound rotor motor and the squirrel cage rotor isthat the conductors of the wound rotor consist of wound coilsinstead of bars. These coils are connected through slip ringsand brushes to external variable resistors. The rotating magnetfield induces a voltage in the rotor windings. Increasing theresistance of the rotor windings causes less current to flowin the rotor windings, decreasing rotor speed. Decreasing theresistance causes more current to flow, increasing rotor speed

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Slip Ring

Brush

Wound Rotor

External Variable Resistors

Synchronous Motor Another type of three-phase AC motor is the synchronousmotor. The synchronous motor is not an induction motor. Onetype of synchronous motor is constructed somewhat like asquirrel cage rotor. In addition to rotor bars, coil windings arealso used. The coil windings are connected to an external DCpower supply by slip rings and brushes.

When the motor is started, AC power is applied to the stator,

and the synchronous motor starts like a squirrel cage rotor.DC power is applied to the rotor coils after the motor hasaccelerated. This produces a strong constant magnetic fieldin the rotor which locks the rotor in step with the rotatingmagnetic field. The rotor therefore turns at synchronous speedwhich is why this is a synchronous motor.

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External DC

Power Supply

Slip Ring

Brush

Rotor Bar

Coil

As previously mentioned, some synchronous motors use apermanent magnet rotor. This type of motor does not need aDC power source to magnetize the rotor.

Review 4

1. The following illustration applies to a _______ polethree-phase AC motor. When winding A1 is a southpole, winding A2 is a _______ pole.

2. The speed of the rotating magnetic field is referred toas the motors _______ speed.

3. The synchronous speed of a 60 Hz, four-pole motor is_______ RPM.

4. The difference in speed between synchronous speedand rotor speed is called _______.

5. A 2-pole motor is operating on a 60 Hz power supply.The rotor is turning at 3450 RPM. Slip is _______%.

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Motor Specifications

Nameplate The nameplate of a motor provides important informationnecessary for proper application. For example, The followingillustration shows the nameplate of a 30 horsepower (H.P.)three-phase (3 PH) AC motor.

Made in Mexico by SIEMENSUS

R

NEMA PREMIUM EFFICIENT

35.0

1LE2321-2CB21-2AA3

SD100

30.00

1775

F B

CONT 40oC AMB.

G 93.6

286T

1.15

460

60

50BC03JPP3 50VC03JPP3

The following paragraphs explain some of the other nameplatinformation for this motor.

Voltage Source (VOLTS) and AC motors are designed to operate at standard voltages. ThisFull-load Current (AMPS) motor is designed to be powered by a three-phase 460 V

supply. Its rated full-load currentis 35.0 amps.

Base Speed (R.P.M.) and Base speedis the speed, given in RPM, at which the motorFrequency (HERTZ) develops rated horsepower at rated voltage and frequency.

Base speed is an indication of how fast the output shaft willturn the connected equipment when fully loaded. This motorhas a base speed of 1775 RPM at a rated frequency of 60 Hz.

Because the synchronous speed of a 4-pole motor operated at60 Hz is 1800 RPM, the full-load slip in this case is 1.4%. If themotor is operated at less than full load, the output speed will bslightly greater than the base speed.

% Slip =

% Slip = 1.4%

1800 - 17751800

x 100

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Service Factor Service factoris a number that is multiplied by the ratedhorsepower of the motor to determine the horsepower atwhich the motor can be operated. Therefore, a motor designedto operate at or below its nameplate horsepower rating has aservice factor of 1.0.

Some motors are designed for a service factor higher than 1.0,

so that they can, at times, exceed their rated horsepower. Forexample, this motor has a service factor of 1.15. A 1.15 servicefactor motor can be operated 15% higher than its nameplatehorsepower. Therefore this 30 HP motor can be operated at34.5 HP. Keep in mind that any motor operating continuouslyabove its rated horsepower will have a reduced service life.

Insulation Class NEMA defines motor insulation classesto describe theability of motor insulation to handle heat. The four insulationclasses are A, B, F, and H. All four classes identify the allowabletemperature rise from an ambient temperature of 40 C

(104 F). Classes B and F are the most commonly used.

Ambient temperatureis the temperature of the surroundingair. This is also the temperature of the motor windings beforestarting the motor, assuming the motor has been stopped longenough. Temperature rises in the motor windings as soon as thmotor is started. The combination of ambient temperature andallowed temperature rise equals the maximum rated windingtemperature. If the motor is operated at a higher windingtemperature, service life will be reduced. A 10 C increase in

the operating temperature above the allowed maximum can cuthe motors insulation life expectancy in half.

The following illustration shows the allowable temperaturerisefor motors operated at a 1.0 service factor at altitudes nohigher than 3300 ft. Each insulation class has a margin allowedto compensate for the motors hot spot, a point at the centerof the motors windings where the temperature is higher. Formotors with a service factor of 1.15, add 10 C to the allowedtemperature rise for each motor insulation class.

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The motor in this example has insulation class F and a servicefactor of 1.15. This means that its winding temperature isallowed to rise to 155 C with an additional 10 C hot spotallowance.

NEMA Motor Design NEMA also uses letters (A, B, C, and D) to identify motordesignsbased on torque characteristics. The motor in this

example is a design B motor, the most common type. Motordesign A is the least common type. The characteristics of motodesigns B, C and D are discussed in the next section of thiscourse.

Motor Efficiency Motor efficiencyis a subject of increasing importance,especially for AC motors. AC motor efficiency is importantbecause AC motors are widely used and account for asignificant percentage of the energy used in industrial facilities

Motor efficiency is the percentage of the energy supplied to th

motor that is converted into mechanical energy at the motorsshaft when the motor is continuously operating at full loadwith the rated voltage applied. Because motor efficiencies canvary among motors of the same design, the NEMA nominalefficiencypercentage on the nameplate is representative ofthe average efficiency for a large number of motors of the samtype. The motor in this example has a NEMA nominal efficiencof 93.6%.

Both NEMA and the Energy Policy Act of 1992 (EPAct)specif

the same process for testing motor efficiency. In 2001, NEMAestablished the NEMA Premiumdesignation for three-phaseAC motors that meet even higher efficiency standards thanrequired by EPAct. More recently, the Energy Independenceand Security Act of 2007 (EISA)was passed. EISA requiresmost motors manufactured after December 19, 2010 tomeet NEMA Premium efficiency levels. This includes motorspreviously covered by EPAct and some additional categories ofmotors.

Siemens NEMA Premium Efficient motorsmeet NEMA

Premium efficiency standards and Siemens Ultra Efficientmotorswith our exclusive die cast copper rotor technologyexceed NEMA Premium efficiency standards.

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NEMA Motor Characteristics

Standard Motor Designs Motors are designed with speed-torque characteristics tomatch the requirements of common applications. The fourstandard NEMA motor designs, A, B, C, and D, have differentcharacteristics. This section provides descriptions for each ofthese motor designs with emphasis on NEMA design B, themost common three-phase AC induction motor design.

Speed-Torque Curve for Because motor torque varies with speed, the relationshipNEMA B Motor between speed and torque is often shown in a graph, called a

speed-torque curve. This curve shows the motors torque, as

a percentage of full-load torque, over the motors full speedrange, shown as a percentage of its synchronous speed.

The following speed-torque curve is for a NEMA B motor.NEMA B motors are general purpose, single speed motorssuited for applications that require normal starting and runningtorque, such as fans, pumps, lightly-loaded conveyors, andmachine tools.

Using a 30 HP, 1765 RPM NEMA B motor as an example, full-load torque can be calculated by transposing the formula forhorsepower.

HP =Torque (in lb-ft) x Speed (in RPM)

5252

Torque (in lb-ft) =HP x 5252

Speed (in RPM)= 30 x 5252

1765= 89.3 lb-ft

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Starting Torque Starting torque, also referred to as locked rotor torque,isthe torque that the motor develops each time it is started atrated voltage and frequency. When voltage is initially applied tothe motors stator, there is an instant before the rotor turns. Atthis instant, a NEMA B motor develops a torque approximatelyequal to 150% of full-load torque. For the 30 HP, 1765 RPMmotor used in this example, thats equal to 134.0 lb-ft of torque

134.0 lb-ft

89.3 lb-ft

Pull-up Torque As the motor picks up speed, torque decreases slightly untilpoint B on the graph is reached. The torque available at thispoint is called pull-up torque. For a NEMA B motor, this isslightly lower than starting torque, but greater than full-loadtorque.

Breakdown Torque As speed continues to increase from point B to point C, torque

increases up to a maximum value at approximately 200% offull-load torque. This maximum value of torque is referred to asbreakdown torque.The 30 HP motor in this example has abreakdown torque of approximately 178.6 lb-ft.

178.6 lb-ft

134.0 lb-ft

89.3 lb-ftPull-up Torque

Breakdown Torque

Starting Torque

Full-load Torque

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Full-Load Torque Torque decreases rapidly as speed increases beyondbreakdown torque until it reaches full-load torqueat aspeed slightly less than 100% of synchronous speed. Full-load torque is developed with the motor operating at ratedvoltage, frequency, and load. The motor in this example hasa synchronous speed of 1800 RPM and a full-load speed of1765 RPM. Therefore, its slip is 1.9%.

178.6 lb-ft

134.0 lb-ft

89.3 lb-ftPull-up Torque

Breakdown Torque

Full-load Torque

Slip 1.9%

Starting Torque

Speed-torque curves are useful for understanding motorperformance under load. The following speed-torque curveshows four load examples. This motor is appropriately sizedfor constant torque load 1 and variable torque load 1. In eachcase, the motor will accelerate to its rated speed. With constatorque load 2, the motor does not have sufficient starting torquto turn the rotor. With variable torque load 2, the motor cannotreach rated speed. In these last two examples, the motor willmost likely overheat until its overload relay trips.

Variabl

eTorqu

eLoad

1

Varia

bleT

orqu

eLo

ad2

Constant Torque Load 1

Constant Torque Load 2

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Starting Current and Starting current, also referred to as locked rotor current, isFull-Load Current the current supplied to the motor when the rated voltage is

initially applied with the rotor at rest. Full-load currentis thecurrent supplied to the motor with the rated voltage, frequencyand load applied and the rotor up to speed. For a NEMA Bmotor, starting current is typically 600-650% of full-load currenKnowledge of the current requirements for a motor is critical fo

the proper application of overcurrent protection devices.

NEMA A Motor NEMA A motorsare the least common design. NEMA Amotors have a speed-torque curve similar to that of a NEMAB motor, but typically have higher starting current. As a result,overcurrent protection devices must be sized to handle theincreased current. NEMA A motors are typically used in thesame types of applications as NEMA B motors.

NEMA C Motor NEMA C motorsare designed for applications that requirea high starting torque for hard to start loads, such as heavily-loaded conveyors, crushers and mixers. Despite the highstarting torque, these motors have relatively low startingcurrent. Slip and full-load torque are about the same as for aNEMA B motor. NEMA C motors are typically single speedmotors which range in size from approximately 5 to 200 HP.

The following speed-torque curve is for a 30 HP NEMA C motowith a full-load speed of 1765 RPM and a full-load torque of89.3 lb-ft. In this example, the motor has a starting torque of214.3 lb-ft, 240% of full-load torque and a breakdown torque o174 lb-ft.

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214.3 lb-ft

89.3 lb-ft

174 lb-ft

Breakdown Torque

NEMA D Motor The starting torque of a NEMA design D motoris

approximately 280% of the motors full-load torque. This makeit appropriate for very hard to start applications such as punchpresses and oil well pumps. NEMA D motors have no truebreakdown torque. After starting, torque decreases until full-load torque is reached. Slip for NEMA D motors ranges from 5to 13%.

The following speed torque curve is for a 30 HP NEMA D motowith a full-load speed of 1656 RPM and a full load torque of95.1 lb-ft. This motor develops approximately 266.3 lb-ft of

starting torque.

95.1 lb-ft

266.3 lb-ft

Slip 8%

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Review 51. A 30 HP motor with a 1.15 service factor can be

operated at _______ HP.

2. A motor with Class F insulation and a 1.0 service factorhas a maximum temperature rise of _______

oC plus a

_______oC hot spot allowance.

3. The starting torque of a NEMA B motor isapproximately _______% of full-load torque.

4. The maximum torque value on a NEMA B motor speed-torque curve is called _______ torque.

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Derating Factors

Several factors can affect the performance of an AC motor.These must be considered when applying a motor.

Voltage Variation As previously discussed, AC motors have a rated voltage andfrequency. Some motors have connections for more that onerated voltage. The following table shows the most commonvoltage ratings for NEMA motors.

A small variation in supply voltage can have a dramatic affect omotor performance. In the following chart, for example, whenvoltage is 10% below the rated voltage of the motor, the motohas 20% less starting torque. This reduced voltage may preven

the motor from getting its load started or keeping it running atrated speed.

A 10% increase in supply voltage, on the other hand, increasesthe starting torque by 20%. This increased torque may causedamage during startup. A conveyor, for example, may lurchforward at startup. A voltage variation also causes similarchanges in the motors starting and full-load currents andtemperature rise.

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Frequency A variation in the frequency at which the motor operates causechanges primarily in speed and torque characteristics. A 5%increase in frequency, for example, causes a 5% increase in fuload speed and a 10% decrease in torque.

Altitude Standard motors are designed to operate below 3300 feet. Airis thinner, and heat is not dissipated as quickly above 3300 feeMost motors must be deratedfor altitudes above 3300 feet.The following chart shows typical horsepower derating factorsbut the derating factor should be checked for each motor. A 50HP motor operated at 6000 feet, for example, would be derateto 47 HP, providing the 40C ambient rating is still required.

Ambient Temperature The ambient temperature may also have to be considered.

The ambient temperature requirement may be reduced from40C to 30C at 6600 feet on many motors. However, a motorwith a higher insulation class may not require derating in theseconditions.

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AC Motors and AC Drives

Many applications require the speed of an AC motor to vary.The easiest way to vary the speed of an AC induction motor isto use an AC drive to vary the applied frequency. Operating amotor at other than the rated frequency and voltage affect bothmotor current and torque.

Volts per Hertz (V/Hz) The volts per hertz (V/Hz) ratiois the ratio of applied voltageto applied frequency for a motor. 460 VAC is the most commonvoltage rating for an industrial AC motor manufactured for usein the United States. These motors have a frequency rating of

60Hz. This provides a V/Hz ratio of 7.67. Not every motor hasa 7.67 V/Hz ratio. A 230 Volt, 60 Hz motor, for example, has a3.8 V/Hz ratio.

= 7.67 V/HZ = 3.8 V/Hz230 V

60 Hz

460 V

60 Hz

Constant Torque Operation AC motors running on an AC line operate with a constant fluxbecause voltage and frequency are constant. Motors operatedwith constant flux are said to have constant torque. Actualtorque produced, however, is dependent upon the load.

An AC drive is capable of operating a motor with constantflux from approximately 0 Hz to the motors rated nameplatefrequency (typically 60 Hz). This is the constant torque rangeAs long as a constant volts per hertz ratio is maintained themotor will have constant torque characteristics.

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The following graphs illustrate the constant volts per hertz ratioof a 460 volt, 60 Hz motor and a 230 volt, 60 Hz motor operateover the constant torque range. Keep in mind that if the appliefrequency increases, stator reactance increases. In order tocompensate for this, the drive must simultaneously increasevoltage proportionally. Otherwise, stator current, flux, andtorque would decrease.

Constant Horsepower Some applications require the motor to be operated above basspeed. Because applied voltage must not exceed the ratednameplate voltage, torque decreases as speed increases. Thisis referred to as the constant horsepower rangebecause anychange in torque is compensated by the opposite change inspeed.

power in HP =Torque in lb-ft x Speed in RPM

5252

If the motor is operated in both the constant torque andconstant horsepower ranges, constant volts per hertz andtorque are maintained up to 60 Hz. Above 60 Hz, the volts perhertz ratio decreases, with a corresponding decrease in torque

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Reduced Voltage and Recall that when a NEMA B motor is started at full voltage, itFrequency Starting develops approximately 150% starting torque and 600%

starting current. When the motor is controlled by an AC drive,the motor is started at reduced voltage and frequency. Forexample, the motor may start with approximately 150% torquebut only 150% of full load current.

As the motor is brought up to speed, voltage and frequency arincreased, and this has the effect of shifting the motors speedtorque curve to the right. The dotted lines on the followingspeed-torque curve represent the portion of the curve notused by the drive. The drive starts and accelerates the motorsmoothly as frequency and voltage are gradually increased tothe desired speed.

Some applications require higher than 150% starting torque.A conveyor, for example, may require 200% rated torque forstarting. This is possible if the drive and motor are appropriatelsized.

Selecting a Motor AC drives often have more capability than the motor. Drivescan run at higher frequencies than may be suitable for anapplication. In addition, drives can run at speeds too low for secooled motors to develop sufficient air flow. Each motor mustbe evaluated according to its own capability before selecting it

for use on an AC drive.

Harmonics, voltage spikes, and voltage rise times of AC drivesare not identical. Some AC drives have more sophisticatedfilters and other components designed to minimize undesirableheating and insulation damage to the motor. This must beconsidered when selecting an AC drive/motor combination.

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Distance Between the Distance from the drive to the motor must also be taken intoDrive and the Motor consideration. All motor cables have line-to-line and line-to-

ground capacitance. The longer the cable, the greater thecapacitance. Some types of cables, such as shielded cable orcables in metal conduit, have greater capacitance. Spikes occuon the output of AC drives because of the charging currentin the cable capacitance. Higher voltage (460 VAC) and higher

capacitance (long cables) result in higher current spikes. Voltagspikes caused by long cable lengths can potentially shorten thlife of the AC drive and motor.

Service Factor on AC Drives A high efficiency motor with a 1.15 service factor isrecommended when used with an AC drive. Due to heatassociated with harmonics of an AC drive, the 1.15 servicefactor is reduced to 1.0.

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Matching Motors to the Load

One way to evaluate whether the torque capabilities of amotor meet the torque requirements of the load is to comparethe motors speed-torque curve with the speed-torquerequirements of the load.

Load Characteristics Tables A table, like one shown below, can be used to find the loadtorque characteristics. NEMA publication MG 1 is one source o

typical torque characteristics.

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Calculating Load Torque The most accurate way to obtain torque characteristics ofa given load is from the equipment manufacturer. However,the following procedure illustrates how load torque can bedetermined. The following illustration shows a pulley fastenedto the shaft of a load. A cord is wrapped around the pulley withone end connected to a spring scale. Pull on the scale untilthe shaft turns and note the force reading on the scale. Then,

multiply the force required to turn the shaft by the radius ofthe pulley to calculate the torque value. Keep in mind that theradius is measured from the center of the shaft.

Scale

Force

Torque = Force x RadiusRadius

For example, if the radius of the pulley is 1 foot and the forcerequired to turn the shaft is 10 pounds, the torque requirementis 10 lb-ft. Remember that this is just the required startingtorque. The amount of torque required to turn the load can varywith speed.

At any point on the speed-torque curve, the amount of torqueproduced by a motor must always at least equal the torquerequired by its load. If the motor cannot produce sufficienttorque, it will either fail to start the load, stall, or run in an

overloaded condition. This will probably cause protectivedevices to trip and remove the motor from the power source.

Centrifugal Pump In the following example, a centrifugal pump requires a full-loatorque of 600 lb-ft. This pump only needs approximately 20%of full-load torque to start. The required torque dips slightly asthe load begins to accelerate and then increases to full-loadtorque as the pump comes up to speed. This is an example of variable torque load.

600 lb-ft

120 lb-ft

Motor

Centrifugal Pump

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The motor selected in this example is a NEMA B motor that ismatched to the load. In other words, motor has sufficient torquto accelerate the load to rated speed.

Screw Down Actuator In the following example, the load is a screw down actuatorwith a starting torque equal to 200% of full-load torque. Notethat the NEMA B motor chosen for this example does not

provide sufficient torque to start the load.

One solution to this problem is to use a higher horsepowerNEMA B motor. A less expensive solution might be to use aNEMA D motor which has higher starting torque for the samehorsepower rating.

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Review 6

1. According to the derating table provided earlier, a 200HP motor operated at 5500 feet would be derated to_______ HP.

2. The volts per hertz ratio of a 460 Volt, 60 Hz motor is_______ V/Hz.

3. An AC drive in volts-per-hertz mode is in the constant_______ range when it is operating above the motorsbase speed.

4. If the radius of a pulley attached to a load shaft is 2 feet,and the force required to turn the shaft is 20 pounds,the amount of torque required to start the load is_______ lb-ft.

5. Which of the loads in the following illustration is

properly matched to the motor. A. Load 1 B. Load 2 C. Load 3 D. Load 4

Load1

Load

2

Load 4

Load 3

Motor

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Motor Enclosures

A motors enclosure not only holds the motors componentstogether, it also protects the internal components frommoisture and containments. The degree of protection dependson the enclosure type. In addition, the type of enclosure affectthe motors cooling. There are two categories of enclosures:open and totally enclosed.

Open Drip Proof (ODP) Open enclosures permit cooling air to flow through the motor.Enclosure One type of open enclosure is the open drip proof (ODP)

enclosure. This enclosure has vents that allow for air flow. Fan

blades attached to the rotor move air through the motor whenthe rotor is turning. The vents are positioned so that liquids andsolids falling from above at angles up to 15 from vertical cannenter the interior of the motor when the motor is mounted ona horizontal surface. When the motor is mounted on a verticalsurface, such as a wall or panel, a special cover may be neededODP enclosures should be used in environments free fromcontaminates.

Vent

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Totally Enclosed In some applications, the air surrounding the motor containsNon-Ventilated (TENV) corrosive or harmful elements which can damage the internalEnclosure parts of a motor. A totally enclosed non-ventilated (TENV)

motorenclosure limits the flow of air into the motor, but is noairtight. However, a seal at the point where the shaft passesthrough the housing prevents water, dust, and other foreignmatter from entering the motor along the shaft.

Most TENV motors are fractional horsepower. However, integrahorsepower TENV motors are used for special applications.The absence of ventilating openings means that all the heatfrom inside the motor must dissipate through the enclosureby conduction. These larger horsepower TENV motors have anenclosure that is heavily ribbed to help dissipate heat morequickly. TENV motors can be used indoors or outdoors.

Totally Enclosed Fan Cooled A totally enclosed fan-cooled (TEFC) motoris similar to a(TEFC) Enclosure TENV motor, but has an external fan mounted opposite the

drive end of the motor. The fan blows air over the motorsexterior for additional cooling. The fan is covered by a shroud toprevent anyone from touching it. TEFC motors can be used indirty, moist, or mildly corrosive environments.

Cooling Fan

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Explosion Proof (XP) Hazardous duty applications are commonly found inchemical processing, mining, foundry, pulp and paper,waste management, and petrochemical industries. In theseapplications, motors have to comply with the strictestsafety standards for the protection of life, machines and theenvironment.This often requires use of explosion proof (XP)motors.

An XP motor is similar in appearance to a TEFC motor, howevemost XP enclosures are cast iron. In the United States, theapplication of motors in hazardous locations is subject toNational Electrical Code and standards set by UnderwritersLaboratories and various regulatory agencies.

XP100

NEMAPremium

!

!

ATTENTIONWARNING

!Warning

Hazardous (Classified) You should never specify or suggest the type of hazardousLocations location classification, it is the users responsibilityto

comply with all applicable codes and to contact local regulatoryagencies to define hazardous locations. Refer to the NationalElectrical CodeArticle 500 for additional information.

Division I and II Locations Division I locationsnormally have hazardous materials presenin the atmosphere. Division II locationsmay have hazardousmaterial present in the atmosphere under abnormal conditions

Classes and Groups Locations defined as hazardous, are further defined by the clasand group of hazard. For example, Class I, Groups A throughDhave gases or vapors present. Class II, Groups E, F, and Ghave flammable dust, such as coke or grain dust. Class IIIis no

divided into groups. This class involves ignitable fibers and lints

Classes I Class II Class III

Groups A-D Groups E-G Flammable Lint

Gas or Vapor Flammable Dust or Fibers

Examples: Examples: Examples:

Gasoline Coke Dust Textiles

Acetone Grain Dust Saw Dust

Hydrogen

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Mounting

NEMA Dimensions NEMA has standardized motor dimensionsfor a range offrame sizes. Standardized dimensions include bolt hole size,mounting base dimensions, shaft height, shaft diameter, andshaft length. Use of standardized dimensions allows existingmotors to be replaced without reworking the mountingarrangement. In addition, new installations are easier to designbecause the dimensions are known.

Standardized dimensions include letters to indicate thedimensions relationship to the motor. For example, the letter

C indicates the overall length of the motor and the letter Erepresents the distance from the center of the shaft to thecenter of the mounting holes in the feet. Dimensions are foundby referring to a table in the motor data sheet and referencingthe letter to find the desired dimension.

NEMA divides standard frame sizes into two categories,fractional horsepower and integral horsepower. The mostcommon frame sizes for fractional horsepower motorsare42, 48, and 56. Integral horsepower motorsare designatedby frame sizes 143 and above. A Tin the motor frame sizedesignation for an integral horsepower motor indicates thatthe motor is built to current NEMA frame standards. Motorsthat have a Uin their motor frame size designation, are built toNEMA standards that were in place between 1952 and 1964.

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The frame size designation is a code to help identify key framedimensions. The first two digits are used to determine the shaheight. The shaft height is the distance from the center of theshaft to the mounting surface. To calculate the shaft height,divide the first two digits of the frame size by 4. For example, 143T frame size motor has a shaft height of 3 inches (14 4)

The third digit in the integral T frame size number is the NEMAcode for the distance between the center lines of the motorfeet mounting bolt holes. The distance is determined bymatching this digit with a table in NEMA publication MG-1.For example, the distance between the center lines of themounting bolt holes in the feet of a 143T frame is 4.00 inches.

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IEC Dimensions IECalso has standardized dimensions, but these dimensionsdiffer from NEMA standards. An example of the IEC dimensionare shown in the following drawing.

Mounting Positions The typical floor mounting positionsare illustrated in thefollowing drawing, and are referred to as F-1 and F-2 mountingsThe conduit box can be located on either side of the frame to

match the mounting arrangement and position. The standardlocation of the conduit box is on the left-hand side of the motowhen viewed from the shaft end. This is referred to as the F-1mounting. The conduit opening can be placed on any of the fousides of the box by rotating the box in 90 steps.

F-1 Position(Standard) F-2 Position

Conduit Box

Shaft

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With modification, a foot-mounted motor can be mounted ona wall and ceiling. Typical walland ceiling mountsare shownin the following illustration. Wall mounting positions have theprefix Wand ceiling mounted positions have the prefix C.

Assembly W-1

Assembly C-1 Assembly C-2

Assembly W-2 Assembly W-3 Assembly W-4

Assembly W-5 Assembly W-6 Assembly W-7 Assembly W-8

Mounting Faces It is sometimes necessary to connect the motor directly tothe equipment it drives. In the following example a motor isconnected directly to a gear box.

Gear Box

Motor

C-face The face, or the end, of a C-face motorhas threaded boltholes. Bolts to mount the motor pass through mating holes inthe equipment and into the face of the motor.

Threaded Bolt Hole

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D-flange The bolts go through the holes in the flange of a D-flangemotorand into threaded mating holes of the equipment.

Review 7

1. A type of open enclosure that prevents liquids andsolids falling from above at angles up to 15 fromvertical from entering the interior of the motor is an_______ enclosure.

2. A type of enclosure that is closed and uses a fanmounted on the motors shaft to supply cooling air flowis referred to as a _______ enclosure.

3. The letter ____ in a motors frame size designationindicates that the motor is built to current NEMAstandards.

4. The shaft height in inches for an integral horsepowerNEMA motor can be determined by dividing the firsttwo digits of the frame size designation by ____.

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Siemens AC Induction Motors

Siemens manufactures AC induction motors for a wide range oapplications. Our products include motors designed to NEMAor IEC standards, as well as above NEMA motors. This sectionprovides an introduction to these motors. Additional informatiois available on the Siemens Industry, Inc. web site.

General Purpose NEMA Siemens General Purpose NEMA motorsare suitable for aMotors wide range of applications, such as HVAC, material handling,

pump, fan, compressor, and other light duty uses in non-hazardous environments.

These motors are available as totally enclosed fan cooled(TEFC) motors in two efficiency levels, NEMA PremiumEfficientand Ultra Efficient. Siemens NEMA PremiumEfficient motors meet NEMA Premium efficiency standardsand Siemens Ultra Efficient motors with our exclusive die castcopper rotor technology exceed NEMA Premium efficiencystandards.

Our General Purpose NEMA motors are manufactured withlight-weight die cast aluminum frames or with rugged cast ironframes for reliable, long lasting performance.

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Cost Savings with NEMA The following example shows the energy savings over the lifePremium Efficiency Motors of a NEMA Premium efficiency motor. In this example, a 20HP,

1800 RPM, TEFC motor (Motor 1) with an efficiency of 91% ana purchase price of $675 is compared with a Siemens GP100NEMA Premium motor with and efficiency of 93.6% and apurchase price of $1072.

C = P +0.746 x HP x T x R

E

C = motor lifecycle costP = initial purchase price0.746 = HP to kilowatt conversion factorHP = motor full-load horsepowerT = estimated motor lifetime in hoursR = utility kilowatt-hour rateE = efficiency expressed as a decimal value

C = $675 +0.746 x 20 HP x 60,000 Hrs. x $0.08

0.91= $79,373.90

C = $1072 +0.746 x 20 HP x 60,000 Hrs. x $0.08

0.936= $77,584.82

Total Savings = $1789.08

Motor 1 Calculation

GP100 Calculation

Severe Duty Motors Siemens Severe Duty motorsare industry workhorses for usin the toughest chemical processing, mining, foundry, pulp andpaper, waste management, and petrochemical applications.These motors are available with a wide range of application-matched modifications. Siemens SD100 severe duty TEFC

motorsexceed NEMA Premium efficiency standards.Additionally, Siemens SD100 IEEE841 severe duty motorshave been designed to exceed the IEEE 841-2001 standards fothe petroleum and chemical industries.

Hazardous Duty Motors In hazardous duty applications, commonly found in chemicalprocessing, mining, foundry, pulp and paper, wastemanagement, and petrochemical industries, motors have tocomply with the strictest safety standards for the protection oflife, equipment, and the environment. These NEMA Premium

efficient motors are UL listed for hazardous gas environments(Class I, Group D, Class II, Groups F & G, Division 1 or Class I,Groups C & D, Division 1). Upgrading to Class II, Group E in aDivision 1 area is also available.

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XP100

NEMAPremium

!

!

ATTENTIONWARNING

! Warning

XP100 Explosion-proof Motor

Inverter Duty Motors Siemens totally enclosed inverter duty motorsare ratedfor continuous operation in a 40C ambient at altitudes up to3300 feet above sea level. These rugged, high efficient motors

exceed EPAct Efficiency standards and are manufacturedfor Severe Duty and Hazardous Duty adjustable speed driveapplications such as centrifugal fans, pumps, blowers, mixers,machine tools, chemical processing, mining, foundry, pulp andpaper, waste management, and petrochemical.

TEFC Vertical P-Base Motors Siemens TEFC Vertical P-Base motorsare the right choice foapplications such as centrifugal pumps, turbine pumps, coolingtowers, fans, mixers, pulp and paper, petrochemical, irrigation,agriculture, and waste water treatment. These Severe Duty, ca

iron motors exceed EPAct Efficiency standards and are offeredwith a solid shaft for Normal, Medium and In-Line Pump thrustapplications. Equipped with an insulation system that exceedsthe requirements of NEMA MG1 Part 31, Siemens Vertical P-Base motors are suitable for use with variable speed drives.

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IEC Low Voltage Motors Siemens offers a complete range of IEC low voltage motorsin sizes from 0.06 to 1250 kW. The following paragraphssummarize the IEC low voltage motor types available.

IEC Standard Motors (Up to Siemens IEC Standard motorsare characterized by their

Frame Size 315L) flexibility, ruggedness and energy efficiency. In general, allmotors are suitable for converter-fed operation with linevoltages of up to 500 V +10%. These motors are designedto fulfill the requirements of the European and internationalmarkets with an output range from 0.06 to 250 kW.

IEC Non-Standard Motors Siemens IEC motor series N compactincludes outputs(Frame Size 315 and Above) up to 1250 kW (at 50 Hz) in the non-standard range. A

number of technical features provide this motor series with itsruggedness, reliability, and long service life. These motors also

are characterized by their high output for a small frame size andhave an extremely compact, space-saving design. N compactmotors have optimized efficiencies to reduce energy cost.

IEC Explosion Protected Siemens explosion-protected motors exceed basic safetyMotors requirements, operating reliably even under the most extreme

conditions. In hazardous environments such as chemical plantsthe oil industry or gas works, our rugged EEx motors complywith the strictest safety standards for the protection of life,machines and the environment.

IEC Extraction Motors, Siemens smoke extraction motorscan cope with highMarine Motors, Roller Table ambient temperatures safely. In the event of an accident, theyMotors reduce the heat loading on the building and keep access and

escape routes smoke-free. Our certified smoke extractionmotors have been specially developed for buildings andconstruction sites with smoke control systems.

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Specially designed for use on ships below deck and for theoffshore industry, our marine motorsmeet the requirementsof the leading classification authorities (VV, DNV, GL, LRS) andhave type-test certificates up to 200kW output.

Our three-phase roller table motorsfor inverter-fed operationare designed to satisfy the high demands of reversing rolling

mills. They are designed as totally enclosed asynchronous threphase motors with a spheroid graphite iron housing, ring ribs,and strengthened bearing brackets.

IEC Inverter Duty Motors Siemens Low Voltage IEC motors feature the future-orientedinsulation system Durgnit IR 2000(IR= Inverter Resistance).The Durgnit IR 2000 insulation system uses high-qualityenamel wires and insulating materials in conjunction with aresin impregnation that does not contain any solvents. Thesemotors can withstand operation with converters that haveIGBT transistors. This allows all our standard IEC LV motors

to be operated with variable speed drives at voltages up to500V +5%. Our specially developed motors, with specialinsulation for operation up to 690V +5%, reduce the cost andspace when utilized with sinusoidal and dv/dt filters.

IEC Customer-specific In addition to the motors previously listed, Siemens alsoMotors manufactures IEC motors to meet specific customer applicatio

requirements.

Above NEMA Motors Motors that are larger than NEMA frame sizes are referred to a

above NEMA motors. These motors range in power up to18,000 HP and are constructed to meet specific customerrequirements.

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For each frame size, Siemens has standard frame dimensions,similar to NEMA dimensions. The following illustrations showsthe typical types of dimensions provided for an above NEMAmotor.

C

W

XW

2F

X

B

Keyway Length

Yoke Width

AB

AC

XD

XL

AF

2E

E

D

HT

AA

Pipetap

N-W

N

The customer typically supplies specifications for startingtorque, breakdown torque, and full-load torque based onspeed-torque curves obtained from the driven equipmentmanufacturer. There are, however, some minimum torquesthat all large AC motors must be able to develop. These arespecified by NEMA.

Locked Rotor Torque 60% of Full-Load TorquePull-Up Torque 60% of Full-Load TorqueMaximum Torque 175% of Full-Load Torque

Above NEMA motors require the same adjustments for altitudand ambient temperature as integral frame size motors. Whenthe motor is operated above 3300 feet, either a higher classinsulation must be used or the motor must be derated. AboveNEMA motors with class B insulation can easily be modifiedfor operation in an ambient temperature between 40 C and50 C. Motors intended for operation above 50 C ambient

temperature require special modification at the factory.

Siemens manufactures a complete line of large AC squirrel-cage induction motors at our ISO-9001 certified plant inNorwood, Ohio. Many of the motors manufactured in this planare horizontal, foot-mounted motors, but this plant alsomanufactures vertical, flange-mounted motors, and specialtmotors.

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Horizontal, Foot-Mounted Siemens manufactures large, horizontal, foot-mounted motorsAbove NEMA Motors with a variety of enclosures such as: open drip proof (ODP),

weather protected I (WPI),weather protected II (WPII),totally enclosed water-to-air cooled (TEWAC),totallyenclosed air-to-air cooled (TEAAC), and totally enclosedfan cooled (TEFC). The following charts summarize Siemensproduct offerings for large, horizontal, foot-mounted motors.

E nc lo su re T yp e O pe n D rip P ro of/W e a th er P ro te cte d I

S iem ens T ype C G

Descr ipt ionBes t suited to indoor appl icat ions where i t wi ll not be exp osed to extrem e

am bient condi t ions.

Degree of Protect ionIP23 - protected against sol id objects greater than 12 .5 mm and fal l ing

w a te r s ra e d a t a n le s u to 60 d e re es fro m ve rtic al.

Type of Cool ing IC01 - o en a i r ven ti la t ion

Power Range 200 to 10,000 HP

Poles 2 to 16

Frame Sizes 500, 580, 680, 800, and 1120

Voltage 460 to 13 ,200 V (460 t o 690 V u t o 800 HP)

Service Factor 1 .0 ( 1 .1 5 o tio n a l)

Enc losure T ype W e ather P rotec ted II

S iem ens T ype C G II

Descr ipt ionDe signed for outdoor app l icat ions where the m otor is not l ikely to be

ro tec ted b o ther s truc tu res .

Degree of Protect ionIP24 - protec ted aga ins t so lid objec ts greater than 12.5 m m and w ater

s la sh in fro m a n d ire ctio n.



Poles 2 to 16

Frame Sizes 500, 580, 680, 800, and 1120

Voltage 460 to 13 ,200 V (460 t o 690 V u t o 800 HP)


Enc losure T ype W e ather P rotec ted II

S iem ens T ype H -C om pact P LU S S H 710 F ram e

Descr ipt ionDe signed for outdoor app l icat ions where the m otor is not l ikely to be

ro tec ted b o ther s truc tu res .

Degree of Protect ionIPW 24 - protec ted agains t so lid objec ts greater than 12.5 m m and w ater

splashing f rom any direct ion. W extends the rat ing to weather cond itions.


U to 18 ,0 00 H P fo r 2 - o le or 4 - o le

U t o 1 2 ,0 0 0 H P f or 6 o le

U t o 1 0 ,0 0 0 H P f or 8 o le

U t o 7 ,0 0 0 H P f or 1 0 o lePoles 2 to 10

Frame Sizes 710, 712, 714, and 716

Voltage 6,000 to 13,200 V


Power Range

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E nc lo su re T yp e T ota lly En clo se d W a te r-to -A ir C oo le d

S iem ens T ype C G G

Descr ipt ion

Designed for indoor and outdoor appl icat ions w here in ternal par ts mu st be

protected f rom adverse am bient condi tions. Has the ad ded b enef i ts of low

no ise and e f f ic ien t wa te r coo lin .

Degree of Protect ionIP54 - l im its in- f low of du st and protected ag ainst water splashing f rom any

direct ion.

Type of C ool ing ICW 81 - water - to-a i r cooled

Power Range 200 to 10,000 HPPoles 2 to 16

Fram e Sizes 580, 680, 800, and 1120


Serv ice Factor 1 .0 ( 1 .1 5 o t io n a l)

E nc lo su re T yp e T ota lly En clo se d W a te r-to -A ir C oo le d

S iem ens T ype H -C om pact P LU S S H 710 F ram e

Descr ipt ion


protected f rom adverse am bient condi tions. Has the ad ded b enef i ts of low

no ise and e f f ic ien t wa te r coo lin .


direct ion.

Type of C ool ing ICW 81 - water - to-a i r cooledPower Range Up to 18,000 HP for 2-pole or 4-pole

U to 1 2 ,0 0 0 H P f or 6 o le

U to 1 0 ,0 0 0 H P f or 8 o le

U to 7 ,0 0 0 H P f or 1 0 o le

Poles 2 to 10

Fram e Sizes 710, 712, 714, and 716



E nc lo su re T yp e T ota lly En clo se d Air-to -A ir C oo le d

S iem ens T ype C A Z

Descr ipt ion


protected f rom a dverse am bient condit ions. Use s air- to-air tube-type hea te xc ha n e rs .


direct ion.

Type of C ool ing IC611 - to ta ll enc losed a i r -to-a ir cooled wi th shaf t mounted external fan


Poles 2 to 16

Fram e Sizes 580, 680, 800, and 1120



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S iem ens Type H -C om pact PLU S SH 710 F ram e

Descr ipt ion


protected f rom a dverse am bient condit ions. Us es air- to-air tube-type hea t

e xc ha n e rs .

Degree of Protect ionIP54 - l im its in- f low o f dust and protected a gainst water splashing f rom any

direct ion.


U to 18 ,0 00 H P fo r 2 - o le or 4 - o leU to 1 2 ,0 0 0 H P f or 6 o le

U to 1 0 ,0 0 0 H P f or 8 o le

U to 7 ,0 0 0 H P f or 1 0 o le

Poles 2 to 10

Frame S izes 710, 712, 714, and 716



E nc lo su re T yp e T ota lly E nc los ed F an C oo led

S iem ens Type C Z and C G Z

Descr ipt ion


protected f rom a dverse am bient condit ions. Us es cool ing f ins on al l four

uadran ts o f i ts oke and hous in s .


direct ion.

Type of C ool ing IC411 - t ot a ll enc losed f an coo led


Poles 2 to 16

Frame S izes 500, 580, 708, 788, and 880

Voltage 4 6 0 to 1 1 ,0 0 0 V ( 46 0 to 6 9 0 V u to 8 0 0 H P )


Power Range

Vertical, Flange-Mounted Siemens manufactures large, vertical, flange-mounted motors

Above NEMA Motors with a variety of enclosures such as: open drip proof weatheprotected I (WPI), weather protected II (WPII), totallyenclosed air-to-air cooled (TEAAC), and totally enclosedfan cooled (TEFC). The following charts summarize Siemensproduct offerings for large, vertical, flange-mounted motors witthese enclosure types.

Enclosure T ype W e ather P rotec ted I

S iem ens T ype C G V and C G G S

Descr ipt ionBes t suited to indoor appl icat ions where i t wi ll not be exp osed to extrem e

am bient condi t ions.

Degree of Protect ion IP23 - protected against sol id objects greater than 12 .5 mm and fal l ingw a te r s ra e d a t a n le s u to 60 d e re es fro m ve rtic al.



Poles 4 to 16

Frame Sizes 500, 580, 680, 800, and 1120



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E nclosure Type W e ather Pro tected II

S iem ens Type C G IIV and C G IIH S

Descr ipt ionDe signed for outdoor app l icat ions whe re the mo tor is not l ikely to be

ro tec ted b o ther s t ruc tu res .

Degree of Protect ionIP24 - protec ted agains t so l id objec ts greater than 12.5 m m and w ater

s la sh in fro m a n d ire ctio n.

Type of C ool ing IC01 - o en a i r ven ti la ti on


Poles 4 to 16Frame Sizes 500, 580, 680, 800, and 1120




S iem ens Type C AZV

Descr ipt ion


protected f rom a dverse am bient condit ions. Uses air- to-air tube-type hea t

e xc ha n e rs .


direct ion.


Power Range 800 to 3,000 HPPoles 4 to 16

Frame Sizes 680, 800, and 1120



E nc lo su re T ype T ota lly E nc los ed F an C oo led

S iem ens Type C G ZV and C G ZH S

Descr ipt ion


protected f rom a dverse am bient condit ions. Uses cool ing f ins on al l four

uadran ts o f i ts oke and hous in s .


direct ion.

Type of C ool ing IC411 - t ot a ll enc losed f an coo led

Power Range 200 to 900 HP

Poles 2 (4 o r 6 o t io n a l)

Frame Sizes 500 and 580



Large Specialty Motors The highly demanding process industries, from oil productionand refining to chemical processing and power generation,have adopted two rigorous standards set forth by the AmericaPetroleum Institute for motor reliability and performance. API

541-4th editionis for the most critical special purpose motorsand API 547is for severe-duty general purpose motors. Inaddition to the above NEMA motors previously listed, Siemensalso manufactures large, AC specialty motors to API 541-4thedition and API 547 specifications.

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Review 81. Siemens General Purpose NEMA motors are available

with _______ enclosures.

2. Siemens Severe Duty NEMA motors are available intwo efficiency levels, _______ and _______.

3. Siemens totally enclosed inverter duty motors are ratedfor continuous operation in a 40C ambient at altitudesup to ________ feet above sea level.

4. Siemens IEC motors are designed to fulfill therequirements of European and international marketswith an output range from _____ to _____ kW.

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