电气技术专业英语电气技术专业英语

朱一纶 主编朱一纶 主编

中国电力出版社中国电力出版社

Unit 8 Electric motor Unit 8 Electric motor

课件制作课件制作 : : 吴岱曦吴岱曦

IndexIndex

• TextText– 1. Induction Motor 1. Induction Motor – 2. DC motor2. DC motor

• Reading materialsReading materials– 1. Stepping motor 1. Stepping motor – 2. Servo controllers 2. Servo controllers – 3. Linear motor3. Linear motor

• ExercisesExercises– 1. Put the Phrases into English 1. Put the Phrases into English – 2. Put the Phrases into Chinese 2. Put the Phrases into Chinese – 3. Sentence Translation3. Sentence Translation– 4. 4. TranslationTranslation

TextText

• An electric motor (Fig 8.1) uses An electric motor (Fig 8.1) uses electrelectrical energyical energy to produce to produce mechanical enermechanical energygy. The reverse process, which using . The reverse process, which using mechanical energy to produce mechanical energy to produce electrical energy, is accomplished by electrical energy, is accomplished by a a generatorgenerator or dynamo. or dynamo.

• Electric motors are found in household Electric motors are found in household appliances such as fans, refrigerators, appliances such as fans, refrigerators, washing machines, pool pumps, floor washing machines, pool pumps, floor vacuum , and fan-forced ovens, and vacuum , and fan-forced ovens, and many industrial applications are many industrial applications are dependent upon motors (or dependent upon motors (or machines)too, which range from the machines)too, which range from the size of one's thumb to the size of a size of one's thumb to the size of a railroad locomotive. railroad locomotive.

• All loads moved by electric motors All loads moved by electric motors are really moved by magnetism. The are really moved by magnetism. The purpose of every component in a purpose of every component in a motor is to help harness, control, and motor is to help harness, control, and use magnetic force. To move a load use magnetic force. To move a load fast does not require more magnets, fast does not require more magnets, you just move the magnets fast. you just move the magnets fast.

• To move a heavier load or to To move a heavier load or to decrease acceleration time decrease acceleration time (accelerate faster), (accelerate faster), however, however, more more magnets (more torque) are needed. magnets (more torque) are needed. This is the basis for all motor This is the basis for all motor applications.applications.

Fig 8.1 Various Motors Fig 8.1 Various Motors

1. Induction Motor1. Induction Motor

• The induction motor is a three phase The induction motor is a three phase AC motor and is the most widely AC motor and is the most widely used machine. Its characteristic used machine. Its characteristic features are:features are:– Simple and rugged construction Simple and rugged construction – Low cost and minimum maintenance Low cost and minimum maintenance – High reliability and sufficiently high High reliability and sufficiently high

efficiencyefficiency

• An induction motor has basically two An induction motor has basically two parts :parts :– An outside stationary stator having coils An outside stationary stator having coils

supplied with AC current to produce a supplied with AC current to produce a rotating magnetic field; rotating magnetic field;

– An inside rotor attached to the output An inside rotor attached to the output shaft that is given a torque by the shaft that is given a torque by the rotating field. rotating field.

StatorStator ( (Fig 8.2)Fig 8.2)

• The stator is made up of a number of The stator is made up of a number of stampings with slots to carry three stampings with slots to carry three phase windings. It is wound for a phase windings. It is wound for a definite number of poles. The definite number of poles. The windings are geometrically spaced windings are geometrically spaced 120 degrees apart. 120 degrees apart.

Fig 8.2 Stator Fig 8.2 Stator

• Stator laminations are stacked Stator laminations are stacked together forming a hollow cylinder. together forming a hollow cylinder. Coils of insulated wire are inserted Coils of insulated wire are inserted into slots of the stator core.into slots of the stator core.

• Each grouping of coils, together with Each grouping of coils, together with the steel core it surrounds, form an the steel core it surrounds, form an electromagnet. Electromagnetism is electromagnet. Electromagnetism is the principle behind motor operation. the principle behind motor operation. The stator windings are connected The stator windings are connected directly to the power source. directly to the power source.

RotorRotor (Fig 8.(Fig 8.3) 3)

• Two types of rotors are used in Two types of rotors are used in Induction motors - squirrel-cage rotor Induction motors - squirrel-cage rotor and wound rotor. and wound rotor.

Fig 8.Fig 8.3 rotor of an induction 3 rotor of an induction motor motor

• (a) lamination - left (a) lamination - left • (b) (b) The construction of the squirrel cage rotor - rightThe construction of the squirrel cage rotor - right

• The construction of the squirrel cage The construction of the squirrel cage rotor is reminiscent of rotating rotor is reminiscent of rotating exercise wheels found in cages of pet exercise wheels found in cages of pet squirrel. The rotor consists of a stack squirrel. The rotor consists of a stack of steel laminations with evenly of steel laminations with evenly spaced conductor bars around the spaced conductor bars around the circumference.circumference.

• The laminations are stacked together The laminations are stacked together to form a rotor core. Aluminum is die to form a rotor core. Aluminum is die cast in the slots of the rotor core to cast in the slots of the rotor core to form a series of conductors around form a series of conductors around the perimeter of the rotor. Current the perimeter of the rotor. Current flow through the conductors forms flow through the conductors forms the electromagnet. the electromagnet.

• The conductor bars are mechanically The conductor bars are mechanically and electrically connected with end and electrically connected with end rings. The rotor core mounts on a rings. The rotor core mounts on a steel shaft to form a rotor assembly.steel shaft to form a rotor assembly.

• The enclosure (Fig 8.4) consists of a The enclosure (Fig 8.4) consists of a frame and two end brackets (or frame and two end brackets (or bearing housings). The stator is bearing housings). The stator is mounted inside the frame. The rotor mounted inside the frame. The rotor fits inside the stator with a slight air fits inside the stator with a slight air gap separating it from the stator. gap separating it from the stator.

• There is no direct physical There is no direct physical connection between the rotor and connection between the rotor and the stator. The enclosure also the stator. The enclosure also protects the electrical and operating protects the electrical and operating parts of the motor from harmful parts of the motor from harmful effects of the environment in which effects of the environment in which the motor operates. the motor operates.

• Bearings, mounted on the shaft, Bearings, mounted on the shaft, support the rotor and allow it to turn. support the rotor and allow it to turn. A fan, also mounted on the shaft, is A fan, also mounted on the shaft, is used on the motor for cooling. used on the motor for cooling.

Fig 8.4 Induction Motor Fig 8.4 Induction Motor

• The wound rotor motor or slip ring The wound rotor motor or slip ring motor is an induction machine where motor is an induction machine where the rotor comprises a set of coils that the rotor comprises a set of coils that are terminated in slip rings to which are terminated in slip rings to which external impedances can be external impedances can be connected. The stator is the same as connected. The stator is the same as is used with a standard squirrel cage is used with a standard squirrel cage motor.motor.

• By changing the impedance By changing the impedance connected to the rotor circuit, the connected to the rotor circuit, the speed/current and speed/torque speed/current and speed/torque curves can be altered. curves can be altered.

• The slip ring motor is used primarily The slip ring motor is used primarily to start a high inertia load or a load to start a high inertia load or a load that requires a very high starting that requires a very high starting torque across the full speed range. torque across the full speed range.

• By correctly selecting the resistors By correctly selecting the resistors used in the secondary resistance or used in the secondary resistance or slip ring starter, the motor is able to slip ring starter, the motor is able to produce maximum torque at a produce maximum torque at a relatively low current from zero relatively low current from zero speed to full speed. speed to full speed.

• A secondary use of the slip ring A secondary use of the slip ring motor is to provide a means of speed motor is to provide a means of speed control. Because the torque curve of control. Because the torque curve of the motor is effectively modified by the motor is effectively modified by the resistance connected to the rotor the resistance connected to the rotor circuit, the speed of the motor can circuit, the speed of the motor can be alteredbe altered （（ FFig 8.5ig 8.5 ）） . .

Fig 8.5 torque curve modified Fig 8.5 torque curve modified by Rby R22

• Increasing the value of resistance on Increasing the value of resistance on the rotor circuit will move the speed the rotor circuit will move the speed of maximum torque down. If the of maximum torque down. If the resistance connected to the rotor is resistance connected to the rotor is increased beyond the point where increased beyond the point where the maximum torque occurs at zero the maximum torque occurs at zero speed, the torque will be further speed, the torque will be further reduced. reduced.

2. DC motor2. DC motor

• By far the most common DC motor By far the most common DC motor types are the brushed and brushless types are the brushed and brushless types, which use internal and types, which use internal and external commutation respectively to external commutation respectively to create an oscillating AC current from create an oscillating AC current from the DC source - so they are not the DC source - so they are not purely DC machines in a strict sense.purely DC machines in a strict sense.

• The classic DC motor design The classic DC motor design generates an in a wound rotor with a generates an in a wound rotor with a split ring commutator (Fig 8.3), and split ring commutator (Fig 8.3), and either a wound or permanent magnet either a wound or permanent magnet stator, a rotor consists of a coil stator, a rotor consists of a coil wound around a rotor which is then wound around a rotor which is then powered by any type of DC voltage powered by any type of DC voltage source. source.

Fig 8.6 DC motorFig 8.6 DC motor

• Many of the limitations of the classic Many of the limitations of the classic commutator DC motor are due to the commutator DC motor are due to the need for brushes to press against the need for brushes to press against the commutator. This creates friction. At commutator. This creates friction. At higher speeds, brushes have higher speeds, brushes have increasing difficulty in maintaining increasing difficulty in maintaining contact. contact.

• Brushes may bounce off the Brushes may bounce off the irregularities in the commutator irregularities in the commutator surface, creating sparks. This limits surface, creating sparks. This limits the maximum speed of the machine. the maximum speed of the machine. The current density per unit area of The current density per unit area of the brushes limits the output of the the brushes limits the output of the motor. The imperfect electric contact motor. The imperfect electric contact also causes electrical noise. also causes electrical noise.

• Brushes eventually wear out and Brushes eventually wear out and require replacement, and the require replacement, and the commutator itself is subject to wear commutator itself is subject to wear and maintenance. The commutator and maintenance. The commutator assembly on a large machine is a assembly on a large machine is a costly element, requiring precision costly element, requiring precision assembly of many parts. assembly of many parts.

• Some of the problems of the Some of the problems of the brushless DC brushless DC motor motor are eliminated in are eliminated in the brushless design. In this motor, the brushless design. In this motor, the mechanical "rotating switch" or the mechanical "rotating switch" or commutator / brushgear assembly is commutator / brushgear assembly is replaced by an external electronic replaced by an external electronic switch synchronized to the rotor's switch synchronized to the rotor's position. position.

• Brushless motors are typically 85-Brushless motors are typically 85-90% efficient, whereas DC motors 90% efficient, whereas DC motors with brush gear are typically 75-80% with brush gear are typically 75-80% efficient.efficient.

• Brushless DC motors are commonly Brushless DC motors are commonly used where precise speed control is used where precise speed control is necessary, as in computer disk drives necessary, as in computer disk drives or in video cassette recorders, the or in video cassette recorders, the spindles within CD drives, and spindles within CD drives, and mechanisms within office products mechanisms within office products such as fans, laser printers and such as fans, laser printers and photocopiers. photocopiers.

• Modern DC brushless motors range in Modern DC brushless motors range in power from a fraction of a watt to power from a fraction of a watt to many kilowatts. Larger brushless many kilowatts. Larger brushless motors up to about 100 kW rating motors up to about 100 kW rating are used in electric vehicles. are used in electric vehicles.

This is the End of the TextThis is the End of the Text

Reading materialsReading materials

1. Stepping motor1. Stepping motor

• Stepping motors can be viewed as Stepping motors can be viewed as electric motors without commutators. electric motors without commutators. Typically, all windings in the motor Typically, all windings in the motor are part of the stator, and the rotor is are part of the stator, and the rotor is either a permanent magnet or, in the either a permanent magnet or, in the case of variable reluctance motors, a case of variable reluctance motors, a toothed block of some magnetically toothed block of some magnetically soft material. soft material.

• For example, aFor example, a variable reluctance variable reluctance stepping motor hastepping motor hass three windings, three windings, typically connected as shown in the typically connected as shown in the schematic diagram in Figure 8.7, with schematic diagram in Figure 8.7, with one terminal common to all windings. one terminal common to all windings. In use, the common wire typically In use, the common wire typically goes to the positive supply and the goes to the positive supply and the windings are energized in sequence. windings are energized in sequence.

• The rotor in this motor has 4 teeth The rotor in this motor has 4 teeth and the stator has 6 poles, with each and the stator has 6 poles, with each winding wrapped around two winding wrapped around two opposite poles. With winding number opposite poles. With winding number 1 energized, the rotor teeth marked 1 energized, the rotor teeth marked X are attracted to this winding's X are attracted to this winding's poles. poles.

• If the current through winding 1 is If the current through winding 1 is turned off and winding 2 is turned turned off and winding 2 is turned on, the rotor will rotate 30 degrees on, the rotor will rotate 30 degrees clockwise so that the poles marked Y clockwise so that the poles marked Y line up with the poles marked 2. To line up with the poles marked 2. To rotate this motor continuously, we rotate this motor continuously, we just apply power to the 3 windings in just apply power to the 3 windings in sequence.sequence.

Fig8.7 variable reluctance Fig8.7 variable reluctance motor motor

• All of the commutation must be All of the commutation must be handled externally by the motor handled externally by the motor controller, and typically, the motors controller, and typically, the motors and controllers are designed so that and controllers are designed so that the motor may be held in any fixed the motor may be held in any fixed position as well as being rotated one position as well as being rotated one way or the other. way or the other.

• Stepping motors come in a wide Stepping motors come in a wide range of angular resolution. The range of angular resolution. The coarsest motors typically turn 90 coarsest motors typically turn 90 degrees per step, while high degrees per step, while high resolution permanent magnet motors resolution permanent magnet motors are commonly able to handle 1.8 or are commonly able to handle 1.8 or even 0.72 degrees per step. even 0.72 degrees per step.

• With an appropriate controller, most With an appropriate controller, most permanent magnet motors can be permanent magnet motors can be run in half-steps, and some run in half-steps, and some controllers can handle smaller controllers can handle smaller fractional steps. fractional steps.

• Stepping motors can be used in Stepping motors can be used in simple open-loop control systems; simple open-loop control systems; these are generally adequate for these are generally adequate for systems that operate at low systems that operate at low accelerations with static loads, but accelerations with static loads, but closed loop control may be essential closed loop control may be essential for high accelerations, particularly if for high accelerations, particularly if they involve variable loads. they involve variable loads.

2. Servo controllers2. Servo controllers

• Servo controller is a wide category of Servo controller is a wide category of motor control. Common features are:motor control. Common features are:– precise closed loop position control precise closed loop position control – fast acceleration rates fast acceleration rates – precise speed control precise speed control

• Servo motors may be made from Servo motors may be made from several motor types, the most several motor types, the most common beingcommon being– brushed DC motor brushed DC motor – brushless DC motors brushless DC motors – AC servo motors AC servo motors

• Servo controllers use position Servo controllers use position feedback to close the control loop. feedback to close the control loop. This is commonly implemented with This is commonly implemented with encoders, resolvers, and Hall effect encoders, resolvers, and Hall effect sensors to directly measure the sensors to directly measure the rotor's position. rotor's position.

• Others measure the back Others measure the back electromotive force (EMF) in the electromotive force (EMF) in the undriven coils to infer the rotor undriven coils to infer the rotor position, and therefore are often position, and therefore are often called "sensorless" controllers.called "sensorless" controllers.

• A servo may be controlled using A servo may be controlled using pulse-width modulation (PWM). How pulse-width modulation (PWM). How long the pulse remains high (typically long the pulse remains high (typically between 1 and 2 milliseconds) between 1 and 2 milliseconds) determines where the motor will try determines where the motor will try to position itself. to position itself.

• For some applications, there is a For some applications, there is a choice between using servomotors choice between using servomotors and stepping motors. Both types of and stepping motors. Both types of motors offer similar opportunities for motors offer similar opportunities for precise positioning, but they differ in precise positioning, but they differ in a number of ways. Servomotors a number of ways. Servomotors require analog feedback control require analog feedback control systems of some type. systems of some type.

• Typically, this involves a Typically, this involves a potentiometer to provide feedback potentiometer to provide feedback about the rotor position, and some about the rotor position, and some mix of circuitry to drive a current mix of circuitry to drive a current through the motor inversely through the motor inversely proportional to the difference proportional to the difference between the desired position and the between the desired position and the current position. current position.

3. Linear motor3. Linear motor

• A linear motor is essentially an A linear motor is essentially an electric motor that has been electric motor that has been "unrolled" so that, instead of "unrolled" so that, instead of producing a torque (rotation), it producing a torque (rotation), it produces a linear force along its produces a linear force along its length by setting up a traveling length by setting up a traveling electromagnetic field.electromagnetic field.

• Linear motors are most commonly Linear motors are most commonly induction motors or stepper motors. induction motors or stepper motors. You can find a linear motor in a You can find a linear motor in a maglev (Transrapid) train, where the maglev (Transrapid) train, where the train "flies" over the ground, and in train "flies" over the ground, and in many roller-coasters[1] where the many roller-coasters[1] where the rapid motion of the motorless railcar rapid motion of the motorless railcar is controlled by the rail.is controlled by the rail.

• Many designs have been put forward Many designs have been put forward for linear motors, falling into two for linear motors, falling into two major categories, low-acceleration major categories, low-acceleration and high-acceleration linear motors. and high-acceleration linear motors. Low-acceleration linear motors are Low-acceleration linear motors are suitable for maglev trains and other suitable for maglev trains and other ground-based transportation ground-based transportation applications. applications.

• The The Shanghai Maglev TrainShanghai Maglev Train connects the connects the rapid transit network 30.5 km to the rapid transit network 30.5 km to the ShShanghai Pudong International Airport anghai Pudong International Airport (Fig (Fig 8.8). High-acceleration linear motors 8.8). High-acceleration linear motors are normally quite short, and are are normally quite short, and are designed to accelerate an object up to designed to accelerate an object up to a very high speed and then release the a very high speed and then release the object, like roller coasters. object, like roller coasters.

FFig 8.8 ig 8.8 The The Shanghai Maglev TraiShanghai Maglev Train n

• They are usually used for studies of They are usually used for studies of hypervelocity collisions, as weapons, hypervelocity collisions, as weapons, or as mass drivers for spacecraft or as mass drivers for spacecraft propulsion. propulsion.

• The high-acceleration motors are The high-acceleration motors are usually of the linear induction design usually of the linear induction design (LIM) with an active three-phase (LIM) with an active three-phase winding on one side of the air-gap winding on one side of the air-gap and a passive conductor plate on the and a passive conductor plate on the other side. other side.

• The low-acceleration, high speed and The low-acceleration, high speed and high power motors are usually of the high power motors are usually of the linear synchronous design (LSM), linear synchronous design (LSM), with an active winding on one side of with an active winding on one side of the air-gap and an array of alternate-the air-gap and an array of alternate-pole magnets on the other side. pole magnets on the other side. These magnets can be permanent These magnets can be permanent magnets or energized magnets. magnets or energized magnets.

This is the End ofThis is the End of the Reading materials the Reading materials

ExercisesExercises

• Ready to go?Ready to go?

1. Put the Phrases into 1. Put the Phrases into EnglishEnglish

• 1)1) 异步电动机异步电动机• 2)2) 三相交流电动机三相交流电动机• 3)3) 定子绕组定子绕组• 4)4) 旋转（磁）场旋转（磁）场• 5)5) 鼠笼式转子鼠笼式转子

Show the Answer

• 6)6) 绕线式电动机绕线式电动机• 7)7) 最大转矩最大转矩• 8)8) 在严格意义上在严格意义上• 9)9) 直流电机直流电机• 10)10) 速度控制速度控制

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2. Put the Phrases into 2. Put the Phrases into ChineseChinese

• 11 ）） to produce to produce mechanical energymechanical energy• 22 ）） floor vacuumfloor vacuum

• 33 ）） decrease acceleration timedecrease acceleration time

• 44 ）） produce a rotating magnetic fieldproduce a rotating magnetic field

• 55 ）） the output shaftthe output shaft

Show the Answer

• 66 ）） geometrically spaced 120 geometrically spaced 120 degrees apartdegrees apart

• 77 ）） speed/torque curvespeed/torque curve

• 88 ）） a means of speed controla means of speed control

• 99 ）） oscillating currentoscillating current

• 1010 ）） wear out and require wear out and require replacementreplacement Show the

Answer

3. Sentence Translation3. Sentence Translation

• 11 ）） Electric motors are found in Electric motors are found in household appliances such as fans, household appliances such as fans, refrigerators, washing machines. refrigerators, washing machines.

• 11 ）很多家用电器里都有电动机，例如电风）很多家用电器里都有电动机，例如电风扇，冰箱，洗衣机。扇，冰箱，洗衣机。

• 2) To move a load fast does not 2) To move a load fast does not require more magnets, you just require more magnets, you just move the magnets fast. move the magnets fast.

• 22 ）要让负载转的更快并不需要增加磁场强）要让负载转的更快并不需要增加磁场强度，你只要增加磁场的转速就可以了。度，你只要增加磁场的转速就可以了。

• 3) Two types of rotors are used in 3) Two types of rotors are used in induction motors - squirrel-cage rotor induction motors - squirrel-cage rotor and wound rotor.and wound rotor.

• 33 ）异步电动机的转子分成两种 ）异步电动机的转子分成两种 – – 鼠笼式转鼠笼式转子和绕线式转子。子和绕线式转子。

• 4) By changing the impedance 4) By changing the impedance connected to the rotor circuit, the connected to the rotor circuit, the speed/current and speed/torque speed/current and speed/torque curves can be altered.curves can be altered.

• 44 ）改变转子电路的阻抗，可以改变速度）改变转子电路的阻抗，可以改变速度 //电流曲线和速度电流曲线和速度 // 转矩曲线。转矩曲线。

• 5) The slip ring motor is used 5) The slip ring motor is used primarily to start a high inertia load primarily to start a high inertia load or a load that requires a very high or a load that requires a very high starting torque across the full speed starting torque across the full speed range. range. • 55 ）绕线式电动机最常用的场合是拖动惯性）绕线式电动机最常用的场合是拖动惯性比较大的负载或者需要高起动转矩的负载比较大的负载或者需要高起动转矩的负载起动。 起动。

• 6) The imperfect electric contact also 6) The imperfect electric contact also causes electrical noise.causes electrical noise.

• 66 ）不完善的电接触还会产生电噪声。 ）不完善的电接触还会产生电噪声。

• 7) At higher speeds, brushes have 7) At higher speeds, brushes have increasing difficulty in maintaining increasing difficulty in maintaining contact.contact.

• 77 ）在更高的速度下，电刷更难保持接触状）在更高的速度下，电刷更难保持接触状态。态。

• 8) In brushless DC motor, the 8) In brushless DC motor, the mechanical "rotating switch" or mechanical "rotating switch" or commutator assembly is replaced by commutator assembly is replaced by an external electronic switch an external electronic switch synchronized to the rotor's position.synchronized to the rotor's position.• 88 ）在无刷直流电动机中，机械“旋转开）在无刷直流电动机中，机械“旋转开关”或换向器被和转子位置同步的外置电关”或换向器被和转子位置同步的外置电子开关所取代。子开关所取代。

44 ．． TranslationTranslation

• Without a commutator to wear out, Without a commutator to wear out, the life of a DC brushless motor can the life of a DC brushless motor can be significantly longer compared to a be significantly longer compared to a DC motor using brushes and a DC motor using brushes and a commutator. commutator.

• Commutation also tends to cause a Commutation also tends to cause a great deal of electrical and RF noise; great deal of electrical and RF noise; without a commutator or brushes, a without a commutator or brushes, a brushless motor may be used in brushless motor may be used in electrically sensitive devices like electrically sensitive devices like audio equipment or computers. audio equipment or computers.

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This is the End of the This is the End of the ExercisesExercises

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