1. Electric Motors and Controls
Lesson Plan PSTS: C6-8

2. Anticipated Problems
What is an electric motor, and what are the functions of each part?
What are the types of motor enclosures, and how are these impacted based on the environment?
What are the basic types of electric motors, and what factors must be considered during selection?

3. Anticipated Problems
What are the proper maintenance principles for electric motors?
Why are electrical controls important in agriculture?
What type of maintenance is required for electrical controls?

4. Terms air gap armature asynchronous motors or induction motors
capacitor motors
capacitor-start, capacitor-run motors
capacitor-start motors
commutator
end shields

5. Terms explosion-proof enclosures (EXPL) frame hazardous location (HAZ)
open drip proof (ODP)
permanent-split capacitor motors
repulsion-start induction run motors
rotor
shaded-pole motors

6. Terms single-phase motors soft-start motors split-phase motors stator
synchronous motors
three-phase motors
through bolts or cap screws
winding or coil

7. Terms totally enclosed air over (TEAO)
totally enclosed fan cooled (TEFC)
totally enclosed non-ventilated (TENV)
totally enclosed wash down (TEWD)
universal motors

8. Electric Motor
Electric motors are relatively simple in design and contain a few basic parts:
Rotor
Armature
Stator

9. Electric Motor The rotor is a rotating part in AC motors.
An armature is a rotating part in DC motors that revolves freely within a stationary part.
The stationary part within the armature is a stator.

10. Rotor
The rotor consists of a slotted core made up of thin sections of special soft steel, carefully balanced on a central shaft.
Two types are squirrel-cage and wound-rotors

11. Squirrel-Cage Rotor
A squirrel-cage rotor has slots that contain bare copper, brass, or aluminum bars short-circuited together at each end by end rings.
It also contains a centrifugal device for operating the starting-switch mechanism.

12. Wound-Rotor
A wound-rotor, which is used in a repulsion-start induction motor, has coils of insulated copper wire wound in the rotor slots.
It has a commutator composed of copper segments.
Each segment is insulated from the other segment, and the ends are soldered to individual commutator segments.

13. Wound-Rotor
When the brushes contact these segments, they complete the circuit, thus permitting currents to flow through all of the coils in the rotor in the proper sequence for starting.
They contain a centrifugal device for short- circuiting all the commutator segments when running.

14. Stator
The stator, or stationary part, has insulated copper wire wound in slots to form one or more pairs of magnetic poles.
It is mounted to the frame.

15. Frame & Basic Components
The frame is a structure that provides for mounting the motor when it is in use.
The end shields are devices that house the bearings for the rotor; one end shield contains the starting switch, brushes, and electrical connections.
Through bolts or cap screws are devices used to hold the motor together.

16. Frame & Basic Components
The air gap is the distance between the rotor and the stator that exists to keep the rotor from rubbing on the stator.
The winding or coil is copper wires wound around a core to be used in creating or receiving electromagnetic energy.
The commutator is a split-ring device used to reverse the current.

17. Frame & Basic Components

18. Motor Enclosures
It is important to select the correct type of motor enclosure depending on the environment in which the motor will operate.

19. Open Drip Proof (ODP)
An open drip proof (ODP) is a motor enclosure that allows air to circulate through the windings for cooling purposes.
It is typically used for indoor/clean/dry applications.

20. Totally Enclosed Fan Cooled
A totally enclosed fan cooled (TEFC) is a motor enclosure that prevents the free exchange of air between the inside and outside of a frame.
The frame is not completely air tight. A fan is attached to the shaft; it pushes air over the frame during operation.
The movement of air helps in the cooling process It must be protected from dust, moisture, and precipitation. This type is used on belt-driven inline fans or duct fans.

21. Totally Enclosed Non-Ventilated
A totally enclosed non-ventilated (TENV) is a motor enclosure that relies on convention for cooling; it has no vent openings and no cooling fan.
TENV is tightly enclosed to prevent the exchange of air. However, it is not airtight.
Exposure to dirt and dampness can occur.
It cannot withstand extremely moist or hazardous locations.

22. Totally Enclosed Air Over
A totally enclosed air over (TEAO) is a motor enclosure that is completely enclosed and not self cooling.
It must be cooled by external factors.
These motors require protection from dust, moisture, and precipitation.
They can be found on propeller fans.

23. Totally Enclosed Wash Down
A totally enclosed wash down (TEWD) is a motor enclosure that can withstand high pressure wash-downs and chemical applications.
Found in food-processing facilities where high humidity and/or wet conditions are present

24. Explosion-Proof Enclosure
An explosion-proof enclosure (EXPL) is an explosion-proof motor enclosure and is totally enclosed for hazardous environments.

25. Hazardous Location
A hazardous location (HAZ) is a motor enclosure that can be used to power fans and air compressors.
Used in environments classified as hazardous locations

26. Selecting an Electric Motor
Electric motors differ in how they start and operate as well as in the amount of power they are able to provide.
Also, they will vary in cost because of features and accessories.

27. Selecting an Electric Motor
Single-phase motors are the most common type of electric motor used in the agriculture industry.
These motors do not create a natural rotating magnetic field
They must rely on an additional means to start the rotor motion.
Once the rotor moves, it activates a rotating magnetic field.

28. Selecting an Electric Motor
Synchronous motors are motors that will operate at an exact and constant output speed.
This is designed to the motor and frequency of the AC electrical source supplying power to the motor.
These motors power clocks and timers because of the precise speed that they express.

29. Selecting an Electric Motor
Asynchronous motors or induction motors are motors that contain a rotor with a cage.
Most will exhibit a squirrel cage around the motor in a cylindrical shape.
The cage is made of heavy copper, aluminum, or brass bars.

30. Selecting an Electric Motor
Shaded-pole motors are low-cost motors constructed simply with low starting torque.
They are not electrically reversible and have low efficiencies.
Shaded-pole motors are used for small, light loads (e.g., small fans).

31. Selecting an Electric Motor
Split-phase motors are motors simple in construction and relatively low in first cost.
They have a low starting torque and require a high starting current. Split-phase motors are limited for use on loads that are easy to start.
They are seldom used in sizes larger than 1/3 hp.
Split-phase motors are made for 120- or 240-volt current and are not readily changed from one to the other. They are used on medium-sized fans.

32. Selecting an Electric Motor
Capacitor motors are motors that have starting and running windings in the stator and squirrel- cage rotors.
Used for higher starting torque requirements
They account for the majority of electric motors sold for farm use.

34. Selecting an Electric Motor
Capacitor-start motors are motors that have a capacitor placed in series with the starting winding.
The capacitor often is in a tube-shaped container on the top of the motor.
The capacitor in the starting winding circuit gives these motors greater starting and accelerating torque for the same starting current

35. Selecting an Electric Motor
Capacitor-start, capacitor-run motors are motors that have a capacitor that stays in series with the starting winding while the motor runs.
The starting switch removes only the starting capacitor from the circuit, leaving the starting winding operational.
These operate more efficiently because they require lower line current when running.

36. Selecting an Electric Motor
Permanent-split capacitor motors are motors that use the same value of capacitance in starting and running windings.
They have low starting torques and no starting mechanism.

37. Selecting an Electric Motor
Repulsion-start induction run motors are motors that have the same high starting torque as the capacitor-start motors and can be used for the same type of loads.
They are heavy-duty motors and can be operated on 120 or 240 volts.
Repulsion-start induction run motors have more moving parts and a higher first cost.

38. Selecting an Electric Motor
Universal motors are motors normally found as component parts on portable power tools or appliances.
Sizes range from 1/150 hp to 2 hp.

39. Selecting an Electric Motor
Three-phase motors are motors that are simple in construction, have few moving parts, and require a minimum of maintenance.
They have high starting torque and are used for difficult-to-start loads.
Their size ranges from ¼ hp to as high as 500 hp.
They are easily reversed by switching any two of the three line leads.

40. Selecting an Electric Motor

41. Selecting an Electric Motor
Soft-start motors are motors that may be useful for applications requiring large motors and a low starting torque.
These are single-phase motors.
If three-phase power is available, it is best to use a three-phase motor.

42. Factors for Selection Type of electrical power available—
Alternating current (AC) may be 120, 240, or 208 voltage.
It can be single-phase or three-phase.

43. Factors for Selection
Size of motor—Horsepower ranges differ depending on the motor type.
Shaded pole motors range from 1/500 to 1/2 hp
Split-phase motors range from 1/20 to ¾ hp
Capacitor-start motors range from 1/8 to 10 hp
Three-phase motors range from 1/4 to 500 hp or larger

44. Factors for Selection
Starting load—Some loads are easy to start (e.g., fans or grinding wheels).
There is usually little or no load until the motor reaches full speed.
Some loads require more effort to start than to keep running (e.g., piston-type water pumps, air compressors, and refrigeration units).

45. Factors for Selection
Speed requirements—Some equipment requires higher operating speeds than other equipment.
Although some regulation of speed can be accomplished through pulley selection, motors should be selected to match closely to the needed speed.

46. Factors for Selection
Type of bearings—Depending on size and type, motors may provide a choice between sleeve bearings or ball bearings.
There may be several methods of bearing lubrication.

47. Factors for Selection
Type of mounting—The type of base or method of mounting an electric motor may depend upon the load it drives.
Some may have a resilient mounting to allow for some flexibility
Others are mounted directly to the machine.
Still others may have a mounting bracket welded to the motor housing.

48. Factors for Selection
Environment—Motor enclosures must be selected according to the environment in which they will operate (e.g., dusty, dirty, or wet conditions).
Some may operate in the presence of explosive vapors.

49. Factors for Selection
Efficiency—It is important to select a motor that operates at high efficiency.
High efficiency may require the engine to run at its full load rating. Then the motor will decrease due to under and overload conditions.
A good practice is to run a motor at no less than % full load and not to exceed 125% full load.

50. Factors for Selection

51. Maintenance: Electric Motors
Electric motors can provide years of trouble-free service if they are properly maintained.
A key practice to follow is to read the motor nameplate for information about the voltage and frequency the motor should maintain.
It will be able to run up to the capacity found on the nameplate.

52. Cleaning Electric Motors
Cleaning should take place at least once a year and more often if used in extreme conditions.
The outside should be cleaned before disassembling the motor.
A soft brush and a vacuum cleaner may be used to loosen and remove dust and foreign material.

53. Cleaning Electric Motors
Compressed air may be used if pressure is kept below 25 psi.
Grease or oil may be removed with a cleaning solvent and a brush.
After all parts have been cleaned, they should be dried with a clean cloth.

54. Lubricating Electric Motors
Lubricating the motor with the proper lubricant, in the correct amount, and at the proper time intervals is important.
The manufacturers’ recommendations must be followed.

55. Storing Electric Motors
Motors should be stored in a dry place and kept free from dirt. To prepare a motor for storage:
Wipe the outside free of all dirt and grease.
Check the bearings for lubrication, and add fresh oil or grease as required.
Cover the shaft extension with a coating of grease to prevent rusting.
Wrap the motor with heavy paper to protect it from dust, dirt, and moisture from condensation.

56. Idle Electric Motors
If motors remain idle for long periods of time, they should be turned on and operated for a 15-minute period every couple of weeks.
This allows the motor to warm up and dry out any moisture that may have accumulated.
It also lubricates the bearings.

57. Electrical Controls
Electric motors must be controlled in a way that their power is used when and where it is needed.
They must be used in the most efficient and economical way possible.
The system must provide safety for the operator, the motor, and the equipment.
The primary purpose of electrical controls and motors is to save labor through automation.

58. Electrical Controls

59. Examples
Examples of uses of electric motors and controls are labor-saving equipment used to:
Move grain and feed
Milk dairy cattle
Feed and water livestock
Handle waste
Ventilate buildings
Dry grain

60. Controls
Controls may be used without being associated with electric motors.
One example is photo cells used to control security lights.
Other examples are smoke alarms and trigger alarms in security systems.
Greenhouse operators regulate light levels and misting systems with electrical controls.

61. Automation
Automation depends on the extensive use of time switches, thermostats, pressure switches, humidistats, and other devices used to start and stop electrical equipment without the constant attention of the operator.

62. Basic Maintenance
If properly maintained, electrical controls should provide years of trouble-free service.

63. Basic Maintenance
Clean the controls so heat does not build up and moisture does not accumulate.
Free circulation of air is important for efficient operation of many controls, especially thermostats and humidity controllers.
Wipe the sensing element with a clean cloth to remove any oil film.
Check contacts for rough surfaces and to remove rough projections with a fine file.
Keep oil and grease away from electrical controls.

64. Review Questions
What are the three basic parts of the motor and the function of each?
In what environment would you find a totally enclosed wash down (TEWD) motor enclosure?
List three factors to consider when selecting a motor.
What should be done to prepare a motor for storage?
Give two examples of how motors can be used in agriculture to save labor.