Electric Motors MECH1200 TO THE TRAINER

Electric Motors MECH1200 TO THE TRAINER
This PowerPoint presentation can be used to train people about the basics of electric motors. The information on the slides is the minimum information that should be explained. The trainer notes for each slide provide more detailed information, but it is up to the trainer to decide if and how much of this information is presented also. Additional materials that can be used for the training session are available on under “Energy Equipment” and include: Textbook chapter on this energy equipment that forms the basis of this PowerPoint presentation but has more detailed information Quiz – ten multiple choice questions that trainees can answer after the training session Workshop exercise – a practical calculation related to this equipment Option checklist – a list of the most important options to improve energy efficiency of this equipment Company case studies – participants of past courses have given the feedback that they would like to hear about options implemented at companies for each energy equipment. More than 200 examples are available from 44 companies in the cement, steel, chemicals, ceramics and pulp & paper sectors

Fundamentals of DC Electric Machinery
MECH1200 History Introduction Principle of Operation of Electric Machinery Principle of Operation of AC Synchronous Machines Principle of Operation of DC Machines Types of Electric Machines Construction of DC Machines DC Machine Torque Characteristics DC Machine Speed Control Exercise Questions

History MECH1200 Faraday and Daniell in the lab
Very advanced mechanisms are developed in the middle ages. Development of the steam engine leads to the industrial revolution in the mid 1700’s. Michael Faraday runs the first electric motor experiment in 1821. Faraday and Daniell in the lab A mechanical clock made in 1510 James Watt Images are in the public domain. Source: Wikimedia Commons, Wikimedia Foundation

What is an Electric Motor?
MECH1200 Introduction What is an Electric Motor? Electromechanical device that converts electrical energy to mechanical energy Mechanical energy used to: Rotate pump impeller, fan, blower Drive compressors Lift materials Motors in industry: 70% of electrical load An electric motor is an electromechanical device that converts electrical energy to mechanical energy. The mechanical energy can be used to perform work such as rotating a pump impeller, fan, blower, driving a compressor, lifting materials etc. It is estimated that about 70% of the total electrical load is accounted by motors only. That is why electric motors are termed as “Work Horse” in an industry.

- Electric Motors: convert electrical energy into mechanical energy.
Electric Machinery: - Electric Motors: convert electrical energy into mechanical energy. - Electric Generators: convert mechanical energy to electric energy. The Electric machine is composed of: - Stator - Rotor

MECH1200 The Stator is the stationary part of a motor. The Rotor is a moving component of an electromagnetic system in the electric motor

How Does an Electric Motor Work?
MECH1200 The general working mechanism is the same for all motors and shown in the figure An electric current in a magnetic field will experience a force. If the current carrying wire is bent into a loop, then the two sides of the loop, which are at right angle to the magnetic field, will experience forces in opposite directions. The pair of forces creates a turning torque to rotate the coil. (note: a “torque” is the force that causes the rotation) Practical motors have several loops on an armature to provide a more uniform torque and the magnetic field is produced by electromagnet arrangement called the field coils

Principle of Operation of AC Synchronous Machines
MECH1200 S N N S N S Alternators such as the one shown above are three phase synchronous machines. In synchronous motors, the magnetic field in the stator rotates, and the rotor tries to follow the stator’s magnetic field, i.e. it tries to synchronize itself with it, and thence the name synchronous motor. N S S N

N N S S Principle of Operation of DC Machines Commutation Circuit
When the rotor is energized, it rotates to the most stable position: Every half cycle the current flowing in the rotor switches direction due to commutation, watch: Once the rotor rotates half a cycle, it switches polarity, so that the magnets are again repelling A Stationary magnetic field in the stator An alternating magnetic field in the rotor But how can we make the magnetic field alternate in the rotor? A circuit that uses a commutation technique is used to supply an alternating current into the rotor. N Commutators N S S Brushes (To maintain electrical contact) Commutation Circuit MECH1200

Types of Electric Motors
MECH1200 Types of Electric Motors Electric Motors DC Motors AC Motors Special Purpose Motors Permanent Magnet DC (PMDC) Stepper motor Induction Motor Series Motor Brushless DC motor Hysteresis motor Shunt Motor Reluctance motor Synchronous Motor Compounded Motor Universal motor Separately Excited motor

Alternating Current (AC) Motors Direct Current (DC) Motors
MECH1200 Classification of Motors Electric Motors Alternating Current (AC) Motors Direct Current (DC) Motors Synchronous Induction Three-Phase Single-Phase Self Excited Separately Excited Series Shunt Compound Motors are categorized in a number of types based on the input supply, construction and principle of operation. We will start at looking at various forms of the DC motor such as shunt and series, followed by the AC motors including synchronous and induction motors.

Three types of Motor Load
MECH1200 Three types of Motor Load Motor loads Description Examples Constant torque loads Output power varies but torque is constant Conveyors, rotary kilns, constant-displacement pumps Variable torque loads Torque varies with square of operation speed Centrifugal pumps, fans Constant power loads Torque changes inversely with speed Machine tools In understanding a motor it is important to understand what a motor load means. Load refers to the torque output and corresponding speed required. Loads can generally be categorized into three groups: Constant torque loads are those for which the output power requirement may vary with the speed of operation but the torque does not vary. Conveyors, rotary kilns, and constant-displacement pumps are typical examples of constant torque loads. Variable torque loads are those for which the torque required varies with the speed of operation. Centrifugal pumps and fans are typical examples of variable torque loads (torque varies as the square of the speed). Constant power loads are those for which the torque requirements typically change inversely with speed. Machine tools are a typical example of a constant power load

DC Motors Parts of a DC motor: Armature with windings Brush assembly
MECH1200 DC Motors Parts of a DC motor: Armature with windings Brush assembly Field windings Commutator

Construction of DC Machines
MECH1200 Field Windings: In DC machines, this is the winding in the stator. Note: Permanent magnet dc motors do not have field winding but rather a permanent magnet. Armature Windings: The windings in the rotor . Commutator segments: the method to convert the dc current to an alternating current in the rotor of the dc motor is called commutation. They are connected to the rotor windings, and stay in contact with the brushes. Brushes: pieces made of carbon or graphite and pushed against a spring to maintain electrical contact with the commutator segments. Interpole windings: A third set of windings are mounted on the stator, and connected in series with the rotor to reduce the sparking between brushes and the commutator.

MECH1200 If the armature and field windings are connected in series, then the machine that results is called the DC series machine. If the armature and field windings are connected in parallel, then the machine that results is called the DC shunt machine. If the armature is connected with a field winding in series and another field winding in parallel, then the resulting machine is called the compounded machine. Note that the interpole windings are always connected in series with the rotor.

MECH1200 Name the type of each of the motors A, B, and C shown in the figure below: A: Shunt motor B: Series motor C: Compound motor

MECH1200 DC Motor Construction

MECH1200 Interpole Windings Due to shifting of the magnetic flux lines, arcing and short-circuiting can result Interpole windings counteract this shift and reduces the arcing Are in series with field coils From Wikipedia: Armature reaction in a DC machine In a DC machine, the main field is produced by field coils. In both the generating and motoring modes, the armature carries current and a magnetic field is established, which is called the armature flux. The effect of armature flux on the main field is called the armature reaction. The armature reaction: demagnetizes the main field, and cross magnetizes the main field. The demagnetizing effect can be overcome by adding extra ampere-turns on the main field. The cross magnetizing effect can be reduced by having common poles. Armature reaction is essential in Amplidyne rotating amplifiers. Armature reaction drop is the effect of a magnetic field on the distribution of the flux under main poles of a generator.[1] Since an armature is wound with coils of wire, a magnetic field is set up in the armature whenever a current flows in the coils. This field is at right angles to the generator field, and is called cross magnetization of the armature. The effect of the armature field is to distort the generator field and shift the neutral plane. The neutral plane is the position where the armature windings are moving parallel to the magnetic flux lines. This effect is known as armature reaction and is proportional to the current flowing in the armature coils. The brushes of a generator must be set in the neutral plane; that is, they must contact segments of the commutator that are connected to armature coils having no induced emf. If the brushes were contacting commutator segments outside the neutral plane, they would short-circuit "live" coils and cause arcing and loss of power. Armature reaction causes the neutral plane to shift in the direction of rotation, and if the brushes are in the neutral plane at no load, that is, when no armature current is flowing, they will not be in the neutral plane when armature current is flowing. For this reason it is desirable to incorporate a corrective system into the generator design. These are two principal methods by which the effect of armature reaction is overcome. The first method is to shift the position of the brushes so that they are in the neutral plane when the generator is producing its normal load current. in the other method, special field poles, called interpoles, are installed in the generator to counteract the effect of armature reaction. The brush-setting method is satisfactory in installations in which the generator operates under a fairly constant load. If the load varies to a marked degree, the neutral plane will shift proportionately, and the brushes will not be the correct position at all times. The brush-setting method is the most common means of correcting for armature reaction in small generators (those producing approximately 1000 W or less). Larger generators require the use of interpoles.

MECH1200 Counter (or Back) EMF Recall from 1100: an induced voltage in a wire (or any conductor) results from relative motion of either the wire or the magnetic field. Likewise, as the armature cuts through the magnetic field of the field coils (stator), a voltage is induced. (Think how a generator works.)

Combined Armature and Field Lines of Force
MECH1200 Counter (or Back) EMF Combined Armature and Field Lines of Force

MECH1200 Counter (or Back) EMF This induced voltage causes current to flow in the opposite direction of the applied DC current, thus “countering” it, reducing the overall current and voltage. Counter EMF current is “out of page” (+z direction) Armature current is “into page” (- z direction)

Permanent Magnet DC Motors
MECH1200 Permanent Magnet DC Motors Excellent starting torque Good speed regulation Limited to low HP loads Torque is limited to 150% of rated torque. Reverse direction of rotation by interchanging armature connections.

Series Wound - DC Motors
MECH1200 Series Wound - DC Motors

Series Wound - DC Motors
MECH1200 Series Wound - DC Motors Highest starting torque Not used with loads that are belt or chain coupled Loads should always be directly coupled. Reverse direction of rotation by interchanging armature connections. Cannot be used without a load attached Examples: Locomotives, Cranes, Hoists..

Series Wound – DC Motors
MECH1200 Series Wound – DC Motors Runaway motor at low/no loads High starting torque

Shunt Wound DC Motors Best speed regulation
MECH1200 Shunt Wound DC Motors Best speed regulation Open shunt field winding will cause motor speed to increase to dangerous levels. Field loss relay should always be used. Allows simplified control for reversing the motor.

MECH1200 Shunt Wound DC Motors Field winding are connected in parallel to the armature windings. Field and armature windings can be hooked to same or different sources. “Separately excited” – independent control of armature and field.

Shunt Wound DC Motors Self excited – When constant speed is desired.
MECH1200 Shunt Wound DC Motors Self excited – When constant speed is desired. Field is independent of armature current. Doesn’t provide high starting torque Ex: Elevator, Centrifugal Pumps Separately excited – Can operate above its rated speed. Speed can be increased by weakening the field in the field windings. Results in lower torque Requires two power supplies Ex: Woodworking Machinery, Printing Press

Shunt Wound DC Motors Properties:
MECH1200 Shunt Wound DC Motors Properties: Speed constant independent of load up to certain torque Field winding parallel with armature winding Current = field current + armature current Speed control: insert resistance in armature or field current If field is supplied from a separate source it is called as separately excited DC motor. (Click once) In a shunt motor, the field winding (shunt field) is connected in parallel with the armature winding (A) as shown in the schematic. The total line current is therefore the sum of field current and armature current The following can be said about the speed of shunt motors: (Click once) The speed is practically constant independent of the load (up to a certain torque after which speed decreases) and therefore suitable for commercial applications with a low starting load, such as machine tools (Click once) Speed can be controlled by either inserting a resistance in series with the armature (decreasing speed) or by inserting resistance in the field current (increasing speed)

MECH1200 Shunt Wound DC Motors Reverse direction by switching either armature or field winding polarities

Shunt DC Motor Terminal Characteristics
MECH1200 Question: At which speed should we operate the motor to achieve maximum power? Hint: The power corresponds to the area of the rectangle under the operating point on the speed-torque line. Which of the three rectangles has the largest area? Speed (RPM) No load speed 3000 Maximum power is at 50% of no load speed 2400 1800 Stall point 1200 600 Torque (ft-lb) 5 10

Shunt DC Motor Speed Control
MECH1200 There are three methods to control the speed of a DC motor: 1. Changing the armature voltage. 2. Changing armature resistance (by adding a resistor in series with armature) 3. Change the field (stator) magnetic field Speed (ω) Speed (ω) As Va increases As Ra increases Torque Torque

Compound Wound DC Motors
MECH1200 Compound Wound DC Motors Starting torque : Better than shunt-wound DC motor. Not as good as series-wound DC motor. Speed regulation Better than series-wound DC motor Not as good as with shunt-wound DC motor. Reverse direction of rotation by interchanging armature connections.

DC Motors DC compound motor Good torque and stable speed
MECH1200 DC Motors DC compound motor Good torque and stable speed Suited for high starting torque if high % compounding: cranes, hoists Higher % compound in series = high starting torque Field winding in series and parallel with armature winding A DC compound motor is a combination of shunt and series motor. In a compound motor, the field winding (shunt field) is connected in parallel and in series with the armature winding (A) as shown in the figure. (Click once) For this reason this motor has a good starting torque and a stable speed. (Click once) The higher the percentage of compounding (i.e. percentage of field winding connected in series), the higher the starting torque this motor can handle. (Click once) For example, compounding of 40-50% makes the motor suitable for hoists and cranes, but standard compound motors (12%) are not.

Series DC Motor Terminal Characteristics
MECH1200 Speed (RPM) If the series motor is unloaded, speed increases significantly (this condition is called Runaway, and it must be avoided) Shunt motor Very high starting torque Series motor Torque (ft-lb)

MECH1200 DC Motor Rating Plates

MECH1200 DC STEPPER MOTORS See other videos at:

Resistance-per-winding determines
MECH1200 DC STEPPER MOTORS Voltage Rating provides desired torque Resistance-per-winding determines the current draw of the motor Maximum operating speed Degrees per Step Sets the number of degrees the shaft will rotate for each full step

MECH1200 STEPPER MOTOR CONTROL 4 signal wires fired in the correct sequence will turn the motor

Stepper motor location
MECH1200 Stepper motor location

How does the stepper motor fit in
MECH1200 How does the stepper motor fit in

MECH1200 Stepper motor STEPS

What are Poles in a Motor?
MECH1200 What are Poles in a Motor? Winding(s) which produce the magnetic field(s) necessary to cause the rotor to turn. 3 Phase; 2 Pole Motor

Brushless DC Motors Rotor is permanent magnet
MECH1200 Brushless DC Motors Rotor is permanent magnet Stator is wired to provide rotating magnetic field

Types of Motor Enclosures
MECH1200 Types of Motor Enclosures ODP – Open Drip Proof TENV – Totally Enclosed Non-Ventilating TEFC – Totally enclosed Fan Cooled XP – Explosion Proof

MECH1200 Types of Motor Enclosures ODP – Open Drip Proof Air flows through motor (fan blades help flow) Used in environments free from contaminants

MECH1200 Types of Motor Enclosures TENV – Totally Enclosed Non-Ventilating Protect motor from corrosive and harmful elements Frame fins help to dissipate heat

MECH1200 Types of Motor Enclosures TEFC – Totally enclosed Fan Cooled Similar to TENV except has external fan for cooling

MECH1200 Types of Motor Enclosures XP – Explosion Proof Similar to TEFC but enclosures are cast iron

MECH1200 Hazardous Locations Division I – Hazardous material present in the air as a norm Division II - Hazardous material present in the air as an abnormal event From Wikipedia: Gas divisions or zones In an industrial plant such as a refinery or chemical process plant, handling of large quantities of flammable liquids and gases creates a risk of leaks. In some cases the gas, ignitable vapor or dust is present all the time or for long periods. Other areas would have a dangerous concentration of flammable substances only during process upsets, equipment deterioration between maintenance periods, or during an incident. Refineries and chemical plants are then divided into areas of risk of release of gas, vapor or dust known as divisions or zones. The process of determining the type and size of these hazardous areas is called area classification. Guidance on assessing the extent of the hazard is given in the NFPA 497 Standard, or API 500 and according to their adaptation by other areas gas zones is given in the current edition of IEC For hazardous dusts, the guiding standard is IEC Typical gas hazards are from hydrocarbon compounds, but hydrogen and ammonia are common industrial gases that are flammable. Non-Hazardous Area An area such as a residence or office would be classed as Non Hazardous (safe area), where the only risk of a release of explosive or flammable gas would be such things as the propellant in an aerosol spray. The only explosive or flammable liquid would be paint and brush cleaner. These are classed as very low risk of causing an explosion and are more of a fire risk (although gas explosions in residential buildings do occur). Non hazardous areas on chemical and other plant are present where the hazardous gas is diluted to a concentration below 25% of its lower flammability limit (or lower explosive limit (LEL)). Division 2 or Zone 2 area: This is a step up from the safe area. In this zone the gas, vapor or mist would only be present under abnormal conditions (most often leaks under abnormal conditions). As a general guide for Zone 2, unwanted substances should only be present under 10 hours/year or 0–0.1% of the time.[2] Division 1 or Zone 1 area: Gas, vapor or mist will be present or expected to be present for long periods of time under normal operating conditions. As a guide for Zone 1, this can be defined as 10–1000 hours/year or 0.1–10% of the time.[2] Zone 0 area: Gas or vapor is present all of the time. An example of this would be the vapor space above the liquid in the top of a tank or drum. The ANSI/NEC classification method consider this environment a Division 1 area. As a guide for Zone 0, this can be defined as over 1000 hours/year or >10% of the time.[2]

Hazardous Locations/ Classes
MECH1200 Hazardous Locations/ Classes From

Summary DC motors are: permanent magnet series-wound shunt-wound
MECH1200 DC motors are: permanent magnet series-wound shunt-wound compound-wound

Exercise Questions MECH1200 How does the rotor of a dc motor maintain electrical contact with its commutation circuit? By using brushes that are pushed against a spring. Name two motors that do not need brushes for their rotor windings. Squirrel cage induction motor and the brushless DC motor, and some types of stepper motors Which motor supplies the highest output torque to weight ratio? The series DC motor.

Exercise Questions MECH1200 Why is it not recommended to use brushed dc motors in spacecraft and some aircraft applications? Because in the space environment there is no air to carry away the heat generated by the brushes of the dc motor, causing them to wear very quickly. The same thing applies in the low pressure environment of aircraft. Thus a brushless dc motor is used. In an environment that contains explosive gases, such as in mines, which motor do you recommend using: a) series dc motor b) shunt dc motor c) induction motor d) universal motor

Which motor is recommended for artificial heart applications
MECH1200 Which motor is recommended for artificial heart applications a) Series dc motor b) Shunt dc motor c) Induction motor e) Brushless dc motor What type of machines is used as an electric generator in vehicles to recharge the battery? The synchronous generator What is added to the dc motor to reduce sparking in dc motor brushes? Interpole windings are added.

Which machines have a more complex construction, DC or AC machines?
MECH1200 Which machines have a more complex construction, DC or AC machines? DC machines are much more complex, due to existence of interpoles and commutation circuits. Which motor is potentially dangerous to operate with no load on it? The series dc motor Why series dc motors should not be used in belt drives? Because if the belt breaks, the motor will be unloaded. Series dc motors are dangerous to operate if unloaded, as their speed will increase significantly until the motor is damaged. Which type of motors can operate on both ac and dc power supplies? The universal motor

Electric Motors MECH1200 TO THE TRAINER

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