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[[ | [[Alternating_current_motors|Alternating current {AC)]] induction motors are widely used in the oil and gas industry because of their simplicity, reliability, and low cost. | ||
== Overview == | |||
Induction motors are either single-phase or three-phase. In an induction motor, the actual rotor speed always is less than that of the rotating magnetic field. '''Fig. 1''' shows a typical induction motor and labels its three basic parts: | |||
*Stator | *Stator | ||
*Rotor | *Rotor | ||
*Enclosure | *Enclosure | ||
<gallery widths=300px heights=200px> | <gallery widths="300px" heights="200px"> | ||
File:Vol3 Page 483 Image 0001.png|'''Fig. 1—Typical induction motor (courtesy of Siemens Energy and Automation Inc. and Houston Armature Works Inc.).''' | File:Vol3 Page 483 Image 0001.png|'''Fig. 1—Typical induction motor (courtesy of Siemens Energy and Automation Inc. and Houston Armature Works Inc.).''' | ||
</gallery> | </gallery> | ||
==Stator construction== | == Stator construction == | ||
The stator and the rotor are electrical circuits that perform as electromagnets. The stator is the stationary electrical part of the motor. The stator core of a National Electrical Manufacturers Association (NEMA) motor is made up of several hundred thin laminations that are stacked together to form a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core. | |||
The stator and the rotor are electrical circuits that perform as electromagnets. The stator is the stationary electrical part of the motor. The stator core of a National Electrical Manufacturers Association (NEMA) motor is made up of several hundred thin laminations that are stacked together to form a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core. | |||
Each group of coils and the steel core it surrounds form an electromagnet. Electromagnetism is the principle behind motor operation. The stator windings are connected directly to the power source. | |||
== Rotor construction == | |||
The rotor is the rotating part of the electromagnetic circuit. The most common type of rotor is the "squirrel cage" rotor, so called because it is reminiscent of one of the exercise wheels found in the cages of pet rodents. | |||
The rotor is the rotating part of the electromagnetic circuit. The most common type of rotor is the "squirrel cage" rotor, so called because it is reminiscent of one of the exercise wheels found in the cages of pet rodents. | |||
The squirrel-cage rotor consists of a stack of steel laminations that has evenly spaced conductor bars around its circumference. The stacked laminations form the rotor core. Aluminum is die-cast in the slots of the rotor core to form the series of conductors around the rotor’s perimeter. Current flow through the conductors forms the electromagnet. The conductor bars are mechanically and electrically connected with end rings. The rotor core mounts on a steel shaft to form a rotor assembly. | The squirrel-cage rotor consists of a stack of steel laminations that has evenly spaced conductor bars around its circumference. The stacked laminations form the rotor core. Aluminum is die-cast in the slots of the rotor core to form the series of conductors around the rotor’s perimeter. Current flow through the conductors forms the electromagnet. The conductor bars are mechanically and electrically connected with end rings. The rotor core mounts on a steel shaft to form a rotor assembly. | ||
The wound rotor is another type of induction-motor-rotor construction. A major difference between the wound rotor motor and the squirrel-cage rotor is that the conductors of the wound rotor consist of wound coils instead of bars. These coils are connected through slip rings and brushes to external variable resistors, as shown in '''Fig. 2'''. The rotating magnetic field induces a voltage in the rotor windings that increases the resistance of the rotor windings. This increase in resistance allows less current flow in the rotor windings, which decreases motor speed. Conversely, decreasing the resistance allows more current flow, and so increases motor speed. | The wound rotor is another type of induction-motor-rotor construction. A major difference between the wound rotor motor and the squirrel-cage rotor is that the conductors of the wound rotor consist of wound coils instead of bars. These coils are connected through slip rings and brushes to external variable resistors, as shown in '''Fig. 2'''. The rotating magnetic field induces a voltage in the rotor windings that increases the resistance of the rotor windings. This increase in resistance allows less current flow in the rotor windings, which decreases motor speed. Conversely, decreasing the resistance allows more current flow, and so increases motor speed. | ||
<gallery widths=300px heights=200px> | <gallery widths="300px" heights="200px"> | ||
File:Vol3 Page 483 Image 0002.png|'''Fig. 2—Wound-rotor-motor diagram (courtesy of Houston Armature Works Inc.).''' | File:Vol3 Page 483 Image 0002.png|'''Fig. 2—Wound-rotor-motor diagram (courtesy of Houston Armature Works Inc.).''' | ||
</gallery> | </gallery> | ||
| Line 29: | Line 33: | ||
Wound-rotor induction motors are used in applications of certain types of pump, in mine hoists, mills, and applications where speed reduction is required in the drive application. | Wound-rotor induction motors are used in applications of certain types of pump, in mine hoists, mills, and applications where speed reduction is required in the drive application. | ||
==Stator coil arrangement== | == Stator coil arrangement == | ||
<gallery widths=300px heights=200px> | The schematic in '''Fig. 3''' illustrates the relationship between the stator coils. The coils operate in pairs. This example uses six coils, a pair for each of the three phases. The coils are wrapped around the soft iron core material of the stator. These coils are referred to as motor windings. Each motor winding becomes a separate electromagnet. The coils are wound in such a way that when current flows in them, one coil in a pair is a north pole and the other a south pole. For example, if A1 were a north pole, then A2 would be a south pole. When the current reverses, so does the polarity of the poles. | ||
<gallery widths="300px" heights="200px"> | |||
File:Vol3 Page 484 Image 0001.png|'''Fig. 3—Typical motor-winding diagram (courtesy of Houston Armature Works Inc.).''' | File:Vol3 Page 484 Image 0001.png|'''Fig. 3—Typical motor-winding diagram (courtesy of Houston Armature Works Inc.).''' | ||
</gallery> | </gallery> | ||
==References== | == References == | ||
== Noteworthy papers in OnePetro == | |||
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read | Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read | ||
==External links== | == External links == | ||
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro | Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro | ||
==See also== | == See also == | ||
[[Electrical grounding]] | |||
[[Electrical_grounding|Electrical grounding]] | |||
[[Electrical_distribution_systems|Electrical distribution systems]] | |||
[[Power_factor_and_capacitors|Power factor and capacitors]] | |||
[[Alternating_current_motors|Alternating current motors]] | |||
[[Electrical | [[Electrical_systems|Electrical systems]] | ||
[[ | [[Synchronous_motor|Synchronous motor]] | ||
[[ | [[Motor_specifications|Motor specifications]] | ||
[[ | [[NEMA_motor_characteristics|NEMA motor characteristics]] | ||
[[ | [[Alternating_current_motor_drives|Alternating current motor drives]] | ||
[[Motor | [[Motor_enclosures|Motor enclosures]] | ||
[[ | [[PEH:Electrical_Systems]] | ||
[[ | [[Category:4.1.6 Compressors, engines and turbines]] | ||
Revision as of 19:15, 1 June 2015
Alternating current {AC) induction motors are widely used in the oil and gas industry because of their simplicity, reliability, and low cost.
Overview
Induction motors are either single-phase or three-phase. In an induction motor, the actual rotor speed always is less than that of the rotating magnetic field. Fig. 1 shows a typical induction motor and labels its three basic parts:
- Stator
- Rotor
- Enclosure
Fig. 1—Typical induction motor (courtesy of Siemens Energy and Automation Inc. and Houston Armature Works Inc.).
Stator construction
The stator and the rotor are electrical circuits that perform as electromagnets. The stator is the stationary electrical part of the motor. The stator core of a National Electrical Manufacturers Association (NEMA) motor is made up of several hundred thin laminations that are stacked together to form a hollow cylinder. Coils of insulated wire are inserted into slots of the stator core.
Each group of coils and the steel core it surrounds form an electromagnet. Electromagnetism is the principle behind motor operation. The stator windings are connected directly to the power source.
Rotor construction
The rotor is the rotating part of the electromagnetic circuit. The most common type of rotor is the "squirrel cage" rotor, so called because it is reminiscent of one of the exercise wheels found in the cages of pet rodents.
The squirrel-cage rotor consists of a stack of steel laminations that has evenly spaced conductor bars around its circumference. The stacked laminations form the rotor core. Aluminum is die-cast in the slots of the rotor core to form the series of conductors around the rotor’s perimeter. Current flow through the conductors forms the electromagnet. The conductor bars are mechanically and electrically connected with end rings. The rotor core mounts on a steel shaft to form a rotor assembly.
The wound rotor is another type of induction-motor-rotor construction. A major difference between the wound rotor motor and the squirrel-cage rotor is that the conductors of the wound rotor consist of wound coils instead of bars. These coils are connected through slip rings and brushes to external variable resistors, as shown in Fig. 2. The rotating magnetic field induces a voltage in the rotor windings that increases the resistance of the rotor windings. This increase in resistance allows less current flow in the rotor windings, which decreases motor speed. Conversely, decreasing the resistance allows more current flow, and so increases motor speed.
Fig. 2—Wound-rotor-motor diagram (courtesy of Houston Armature Works Inc.).
Wound-rotor induction motors are used in applications of certain types of pump, in mine hoists, mills, and applications where speed reduction is required in the drive application.
Stator coil arrangement
The schematic in Fig. 3 illustrates the relationship between the stator coils. The coils operate in pairs. This example uses six coils, a pair for each of the three phases. The coils are wrapped around the soft iron core material of the stator. These coils are referred to as motor windings. Each motor winding becomes a separate electromagnet. The coils are wound in such a way that when current flows in them, one coil in a pair is a north pole and the other a south pole. For example, if A1 were a north pole, then A2 would be a south pole. When the current reverses, so does the polarity of the poles.
Fig. 3—Typical motor-winding diagram (courtesy of Houston Armature Works Inc.).
References
Noteworthy papers in OnePetro
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read
External links
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro
See also
Electrical distribution systems