Energy Systems Engineering Technology - Idaho State University

Energy Systems Engineering Technology

College of Technology Motors and Controls Module # 3 AC Generators, Transformers, and AC Motors

Document Intent: The intent of this document is to provide an example of how a subject matter expert might teach AC Generators, Transformers, and AC Motors. This approach is what Idaho State University College of Technology is using to teach its Energy Systems Instrumentation and Control curriculum for AC Generators, Transformers, and AC Motors. The approach is based on a Systematic Approach to Training where training is developed and delivered in a two step process. This document depicts the two step approach with knowledge objectives being presented first followed by skill objectives. Step one teaches essential knowledge objectives to prepare students for the application of that knowledge. Step two is to let students apply what they have learned with actual hands on experiences in a controlled laboratory setting. Examples used are equivalent to equipment and resources available to instructional staff members at Idaho State University. Fundamentals of AC Generators, Transformers, and AC Motors Introduction: This module covers fundamental aspects of AC Generators, Transformers, and AC Motors as essential knowledge necessary to perform work safely according to national and local standards on or around electrical power sources that are associated with motors and controls. Students will be taught the fundamentals of AC Generators, Transformers, and AC Motors using classroom instruction, demonstration, and laboratory exercises to demonstrate knowledge and skill mastery of AC Generators, Transformers, and AC Motors. Completion of this module will allow students AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology to demonstrate mastery of knowledge and skill objectives by completing a series of tasks demonstrating safe work practices on or around electrical power sources.

References This document includes knowledge and skill sections with objectives, information, and examples of how Motors and Control could be taught in a vocational or industry setting. This document has been developed by Idaho State University’s College of Technology. Reference material used includes information from: American Technical Publication – Electrical Motor Controls for Integrated Systems, Third Edition, by Gary J. Rockis and Glen A. Mazur, ISBN 0-8269-1207-9 (Chapter 7) National Electrical Code® International Electrical Code® Series, NFPA 70TM, NEC 2008, ISBN-13: 978-087765790-3

AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology STEP ONE AC Generators, Transformers, and AC Motors Course Knowledge Objectives Knowledge Terminal Objective (KTO)

KTO 3. 1.

ANALYZE AC Generators, Transformers, and AC Motors to compare advantages and disadvantages to ensure they are correctly selected for applications according to manufacturing specifications and electrical requirements

Knowledge Enabling Objectives (KEO)

KEO 3. 1.

DESCRIBE what an AC GENERATOR consists of and its principle of operation.

KEO 3. 2.

DESCRIBE how a SINGLE-PHASE AC GENERATOR provides AC Power.

KEO 3. 3.

EXPLAIN how a three phase AC GENERATOR provides AC Power to include operational characteristics and how they are connected to power AC loads.

KEO 3. 4.

Place Holder for Lawrence Beaty AC Generator Objective on how it is taught and differs from Text Book.

KEO 3. 5.

EXPLAIN three classifications of VOLTAGE CHANGES to include how they occur, and how they are compensated.

KEO 3. 6.

DESCRIBE a TRANSIENT VOLTAGE is and how devices can be protected from High-Level Transients.


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Energy Systems Engineering Technology KEO 3. 7.

DESCRIBE what a TRANSFORMER is and how it effects Voltage.

KEO 3. 8.

EXPLAIN what TRANSFORMER LOSSES are and how they can be minimized.

KEO 3. 9.

EXPLAIN how SINGLE-PHASE and THREE PHASE TRANSFORMER CONNECTIONS are made to include both Primary and Secondary Taps.

KEO 3. 10.

EXPLAIN what a CONTROL TRANSFORMER is and how they provide control voltage lower than the Primary Voltage applied.

KEO 3. 11.

DESCRIBE two methods used to TROUBLESHOOT TRANSFORMERS.

KEO 3. 12.

DESCRIBE what a SINGLE PHASE AC MOTOR consists of, its construction, and principle of operation to include advantages they have over DC MOTORS.

KEO 3. 13.

DESCRIBE three types of SINGLE PHASE AC MOTORS to include: ShadedPole, Split-Phase, and Capacitor motors.

KEO 3. 14.

DESCRIBE what a THREE PHASE AC MOTOR is to include operational uses, and advantages they have over both DC Motors and AC SINGLE PHASE Motors.

KEO 3. 15.

DESCRIBE SINGLE VOLTAGE and DUAL VOLTAGE THREE PHASE MOTOR applications to include WYE and DELTA Connections.

KEO 3. 16.

DESCRIBE AC MOTOR TROUBLESHOOTING TECHNIQUES to include: Troubleshooting Single Phase Shaded-Pole, Split-Phase, and Capacitor Motors, and Three Phase Motors.


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Energy Systems Engineering Technology AC Generators, Transformers, and AC Motors

KEO 3. 1.

DESCRIBE what an AC GENERATOR consists of, its components, and its principle of operation.

AC GENERATORS convert mechanical energy into electrical energy (the same way a DC Generator does) by means of electromagnetic induction. AC GENERATORS are actually referred to as ALTERNATORS because they convert mechanical energy into AC Voltage and Current (Alternating Current) They are similar to DC Generators in that both generators have Field Winding and an Armature that rotates in a magnetic field. AC GENERATORS consists of a Field Winding, an Armature (Coil), Slip Rings and Brushes as depicted in the below picture:

Figure 7-1 page 141 

Field Windings are magnets used to produce the magnetic field in a generator. The magnetic field can be provided by permanent magnets or by Electromagnets. Most AC


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Energy Systems Engineering Technology Generators have their magnetic field generated by Electromagnets. Electromagnets are supplied with an external current to keep the magnetic field at its desired magnetic strength. 

An Armature (Coil) is the movable coil of wire that rotates through the magnetic field. An Armature (Coil) may consist of many coils (similar to the armature in a DC generator). The difference between the DC Generator and the AC Generator is: o In a DC Generators Armature the ends of the coil(s) are attached to a commutator. o In n AC Generators Armature the ends of the coil(s) are attached to slip rings.



Slip Rings are metallic rings connected to the ends of the armature coils(s) and are used to connect the induced voltage to the generators brushes. When the armature is rotated in the magnetic field, a voltage is generated in each half of the armature coil. This voltage is illustrated in the below sine wave of one revolution:

An AC Generator uses slip rings, which will allow the output current and voltage to oscillate through positive and negative values. This oscillation of voltage and current takes the shape of a sine wave. This is typical of the AC Voltage we have in our homes and industry throughout the world.


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Energy Systems Engineering Technology In DC Generators, a commutator is used to provide an output whose current always flowed in the positive direction as illustrated in the below figure:



Brushes in an AC Generator are the sliding contact that rides against the slip rings and is used to connect the armature to the external AC Circuit. As the armature is rotated, each half cuts across the magnetic lines of force at the same speed. Thus the strength of the voltage induced in one side of the armature is always the same strength of the voltage induced in the other side of the armature. Each half of the armature cuts the magnetic lines of force in a different direction. As the armature rotates in the clockwise direction, the lower half of the coil cuts the magnetic lines of force from the bottom up to the to the left, while the top half of the coil cuts the magnetic lines of force from the top down to the right. The voltage induced in one side of the coil, therefore, is opposite to the voltage induced in the other side of the coil. The voltage in the lower left half of the coil enables current flow in one direction, and the voltage in the upper half enables current flow in the opposite direction. This means the voltage and current alternates in both directions as is why it is called ALTERNATING CURRENT VOLTAGE (AC Voltage). Since the two halves of the coil(s) are connected in a closed loop, the voltages add to each other. The result is that the total of a full rotation of the armature is twice the voltage of each coil(s) half. This total voltage is obtained at the brushes connected to the slip rings, and is applied to an external circuit.


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DESCRIBE how a SINGLE-PHASE AC GENERATOR provides AC Power.

A SINGLE-PHASE AC GENERATOR provides power through each complete rotation of its armature within its magnetic field coils and produces one complete alternating current cycle. The following picture depicts how the armature rotates 3600 as it generates continuously changing AC Sine Wave:

Figure 7-2 page 143 AC Generators, Transformers, and AC Motors Module

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In the above picture, in position “A”, before the armature begins to rotate in a clockwise direction, there is no voltage and no current in the external load circuit because the armature is not cutting across any magnetic lines of force (O0 of rotation). 

As the armature rotates from position “A” to position “B”, each half of the armature cuts across the magnetic lines of force, producing current in the external circuit. The current increases from zero to maximum value in one direction. This changing value of current is represented by the first quarter (900 of rotation) of the sine wave.



As the armature rotates from position “B” to position “C”, the current continues in the same direction. The current decreases from its maximum positive value back to zero. This changing value of current is represented by the second quarter (910 - 1800 of rotation) of the sine wave.



As the armature continues to rotate to position “D”, each half of the coil cuts across the magnetic lines of force in the opposite direction. This changes the direction of current. During this time, the current increases from its maximum negative value. This changing value of current is shown by the third quarter (1810 – 2700 of rotation) of the sine wave. As the armature completes its rotation to position “E” (position “A”), the current is deceased to zero, thus completing one 3600 cycle of the sine wave.

KEO 3. 3.

EXPLAIN how a three phase AC GENERATOR provides AC Power to include operational characteristics and how they are connected to power AC loads.

The same principles of a single phase AC Generator are the same for the three phase AC Generator except that there are there equally spaced armature windings 1200 out of phase with each other.


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Energy Systems Engineering Technology The below picture illustrates the differences between a single and a three phase generator showing how three equally spaced armature windings 1200 out of phase will create three output voltages 1200 out of phase with each other:

Figure 7-3 page 144 A Single Phase Generator has two leads providing power to the intended load. It is alternating current that flow in both a positive and negative relationship to the (above and below) the 0 volt reference point. Because a Three Phase Generator has three separate armature windings so there are six leads providing power to the intended load. AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology When the six leads are brought out from the Three Phase Generator, they are connected so that only three leads appear for connection to the three different armature circuits. There are two connections: Delta and Wye; the manner in which they are connected determines the electrical characteristics of the generators output. The following picture depicts both the Delta and Wye connections of a three phase generator:


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Energy Systems Engineering Technology 

A Delta Connection is a connection that has each coil end connected end-to-end to form a closed loop. In a Delta Connection, the three windings are all connected in series and form a closed circuit. A Delta Connection appears like the Greek Letter Delta (Δ).



A Wye Connection is a connection that has one end of each coil connected together and the other end of each coil left open for external connections. A Wye Connection appears as the letter Y. NOTE

The reasoning for the Delta and Wye Connections will be addressed later in this curriculum as it has to do with AC Power distribution systems and AC Power connections to three phase motors. SUMMARY:             

AC GENERATORS convert mechanical energy into electrical energy (the same way a DC Generator does) by means of electromagnetic induction. AC GENERATORS consists of a Field Winding, an Armature (Coil), Slip Rings and Brushes. Field Windings are magnets used to produce the magnetic field in a generator. An Armature (Coil) is the movable coil of wire that rotates through the magnetic field. Slip Rings are metallic rings connected to the ends of the armature coils(s) and are used to connect the induced voltage to the generators brushes. Brushes in an AC Generator are the sliding contact that rides against the slip rings and is used to connect the armature to the external AC Circuit. A SINGLE-PHASE AC GENERATOR provides power through each complete rotation of its armature within its magnetic field coils and produces one complete alternating current cycle. The same principles of a single phase AC Generator are the same for the three phase AC Generator except that there are there equally spaced armature windings 1200 out of phase with each other. A Single Phase Generator has two leads providing power to the intended load. A Three Phase Generator has three separate armature windings so there are six leads providing power to the intended load. There are two connections: Delta and Wye; the manner in which they are connected determines the electrical characteristics of the generators output. A Delta Connection is a connection that has each coil end connected end-to-end to form a closed loop A Wye Connection is a connection that has one end of each coil connected together and the other end of each coil left open for external connections.


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Place Holder for Lawrence Beaty AC Generator Objective on how it is taught and differs from Text Book.

KEO 3. 5.

EXPLAIN three classifications of VOLTAGE CHANGES to include how they occur, and how they are compensated.

VOLTAGE CHANGES need to be monitored and controlled. AC Generators are designed to produce an out voltage. In addition, all electrical and electronic equipment is rated for operation at a Specific Voltage. The standard rated voltage is a voltage that equipment can operate safely can vary in a range of +5% to -10% of the equipments voltage requirements. This voltage range is used because an Over-Voltage is generally more damaging than an Under-Voltage condition. Equipment Manufacturers, Utility Companies, and regulating agencies must routinely compensate for changes in system voltage. Backup Generators are used to compensate for voltage changes. A Backup Generator can be powered by diesel, gasoline, natural gas, or propane engines connected to the generator. If there is any power interruption in the time period between the loss of main utility power and when the generator starts providing power, the generator is usually classified as a standby (emergency) power supply. VOLTAGE CHANGES in a system may be categorized as: Momentary, Temporary, or Sustained as depicted in the below picture:


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Energy Systems Engineering Technology 

A Momentary Power Interruption is a decrease to 0 Volts on one or more of the three phase power lines lasting from .5 cycles up to 3 seconds. All power distribution systems have momentary power interruptions during normal operation. The interruptions can be caused when Lightning Strikes Nearby, Utility Grid Switching during a problem (short on one line, or during Open Circuit Transition Switching (a process in which power is momentarily disconnected when switching a circuit from one voltage supply or level to another).



A Temporary Power Interruption is a decrease to 0 Volts on one or more power lines lasting more than 3 seconds up to 1 minute. Automatic circuit breakers and other circuit protection equipment protect all power distribution systems. Circuit protection equipment is designed to remove faults and to restore power. Automatic circuit breakers normally take 20 cycles to about 5 seconds to close. If the power is restored, the power interruption is only temporary. A Temporary Power Interruption can also be caused by a time gap between power interruptions and when a back-up power supply (generator) takes over, or if someone accidently opens the circuit by switching the wrong circuit breaker and then turns it back on.



A Sustained Power Interruption is a sustained power interruption when the power decreases to 0 Volts on all power lines for a period of longer than one minute. All power distribution systems have a complete loss of power at some time. They are caused as a result of Storms, Tripped Circuit Breakers, Blown Fuses, and or Damaged Equipment.

The effect of a power interruption on a load depends on the load and the application. If a power interruption could cause equipment, production, and or security problems that are not acceptable, an Uninterruptable Power System/Supply (UPS) can be utilized. An Uninterruptable Power System/Supply (UPS) is a power supply that provides constant power needs when the main power supply is interrupted. This is accomplished by a network of electronics and batteries such that the incoming AC power from the main utility is used to convert the AC to DC to keep the batteries charged and then it inverts the DC back to clean uninterrupted and filtered AC power to which the facility that utilizes this UPS will not experience a power interruption upon loss of the main utility power source. A large facility will also have a backup generator with a UPS to pick up the emergency designated power in the event the UPS main battery(s) lose their ability to keep their charge. For long power interruption protection (sustained), a combination of a generator and a UPS are used. For short power interruptions (temporary), a UPS is used. UPS batteries are generally sealed lead acid batteries. AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology Uninterruptable Power System/Supplies (UPS) are also used to keep loads like important business computing systems and medical equipment powered up at all times in the event of a power loss. These UPS units have the load running directly from them and are constantly being kept charged by the facilities main power source. An example of a Common UPS is the power supply provided to a laptop computer. When the laptop is plugged into a power source, it keeps the internal battery charged. When the laptop is not plugged into a power source, it is running off the internal battery. The internal battery provides power to the laptop with or without an outside power supply as long as the battery can last without being charged. There are also Portable AC Generators of various sizes used to provide power during temporary power interruptions as depicted below:

Picture at bottom of page 146 These generators are utilized in Recreational Vehicles to provide AC power when they are not connected to a power supply in and on construction sites where power has not yet been established, and in residences for temporary power outages. NOTE: Portable generators SHOULD NEVER be connected to a residence or utility power source to back-feed AC power when the utility power has been lost. This is because the portable generator and utility power are not synchronized and this could cause a fire and or explosion, which can cause death or injury as well as serious equipment damage. AC Backup Generators are designed for temporary or sustained power interruptions. They are provided with an automatic transfer switch that senses loss of power, starts the generator, and picks up essential or emergency power loads. AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology When the power is restored, the transfer switch automatically resets and allows only the utility power to be available without a second power loss (this transfer is instantaneous). When power is initially lost, there is a short interruption of incoming power until the generator comes up to speed and assumes the load. There is no interruption upon return of the incoming utility power. The following two pictures are of a backup generator:

Backup 120/240 VAC Natural Gas Generator

Backup Generator Transfer Switch connected to a residential 120/240 VAC Main Power Panel. AC Generators, Transformers, and AC Motors Module

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SUMMARY:           



VOLTAGE CHANGES need to be monitored and controlled. An Over-Voltage is generally more damaging than an Under-Voltage condition. Equipment Manufacturers, Utility Companies, and regulating agencies must routinely compensate for changes in system voltage. Backup Generators are used to compensate for voltage changes and can be powered by diesel, gasoline, natural gas, or propane engines connected to the generator. VOLTAGE CHANGES in a system may be categorized as: Momentary, Temporary, or Sustained. A Momentary Power Interruption is a decrease to 0 Volts on one or more of the three phase power lines lasting from .5 cycles up to 3 seconds. A Temporary Power Interruption is a decrease to 0 Volts on one or more power lines lasting more than 3 seconds up to 1 minute. A Sustained Power Interruption is a sustained power interruption when the power decreases to 0 Volts on all power lines for a period of longer than one minute. Uninterruptable Power System/Supplies (UPS) are also used to keep loads like important business computing systems and medical equipment powered up at all times in the event of a power loss. UPS units have the load running directly from them and are constantly being kept charged by the facilities main power source. Portable generators SHOULD NEVER be connected to a residence or utility power source to back-feed AC power when the utility power has been lost. This is because the portable generator and utility power are not synchronized and this could cause a fire and or explosion, which can cause death or injury as well as serious equipment damage. Portable generators can be used to provide temporary power to essential loads by the use of extension cords plugged directly to an essential load like a heater or refrigerator that has been unplugged from the utility powered receptacle.


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DESCRIBE a TRANSIENT VOLTAGE is and how devices can be protected from High-Level Transients.

A TRANSIENT VOLTAGE is a temporary, unwanted voltage in an electrical circuit. Transient Voltages are normally erratic, large voltages or spikes that have a short duration and a shout rise time. Devices like Computers, Electronic Circuits (TVs – Micro Wave Ovens – Sound Systems etc) require protection against Transient Voltages. Protection methods usually include proper wiring to National Electrical Code Requirements, to include grounding, shielding of the power lines, and use of Surge Protectors. 

A Surge Protector is an electrical device that provides protection from high-level transient voltages by limiting the level of voltage allowed downstream from the Surge Protector/Suppressor (more commonly called a Surge Suppressor). Surge Protector/Suppressors can be installed at service entrance panels and individual loads as depicted in the below picture:


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Energy Systems Engineering Technology Surge Suppressors power strips as shown above generally will have and on off switch and a reset button. When they trip the power is removed from the loads and the device needs to be manually reset to restore power to the loads. If the power surge was high enough, it could actually damage the Suppressor and it will not reset. Surge Suppressors are under a UL listing and requirements (IEC 61643-1, EN 61643-11 and 21 , Telcordia Technologies Technical Reference TR-NWT-001011, ANSI / IEEE C62.xx, or UL) and mandated that all units manufactured after August 17, 1998 must pass all test procedures outlined in the second edition of UL1449 to continue to be listed and labeled as UL1449.

SUMMARY:       

Transient Voltages are normally erratic, large voltages or spikes that have a short duration and a shout rise time. Devices like Computers, Electronic Circits (TVs – Mircro Wave Ovens – Sound Systems etc) require protection against Transient Voltages. Protection methods usually include proper wiring to National Electrical Code Requirements, to include grounding, shielding of the power lines, and use of Surge Protectors. A Surge Protector is an electrical device that provides protection from high-level transient voltages by limiting the level of voltage allowed downstream from the Surge Protector/Suppressor (more commonly called a Surge Suppressor). Surge Suppressors power strips generally have and on off switch and a reset button. When Surge Suppressors trip the power is removed from the loads and the device needs to be manually reset to restore power to the loads. If the Power Surge was high enough, it could actually damage the Suppressor and it will not reset.

KEO 3. 7.

DESCRIBE what a TRANSFORMER is and how it effects Voltage.

A TRANSFORMER is an electrical device that uses electromagnetism to change voltage from one level to another. In other words, the Voltage is Stepped Up or Stepped Down. Transformers are used in electrical distribution systems to increase or decrease the voltage and current safely and efficiently. They are used to increase voltage to a High Level for Transmission across the country and then to decrease that voltage to a Low Level for use to a variety of electrical loads (residential, commercial, and industrial). AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology An example of how Transformers accomplish this is depicted in the below picture:

Figure 7-7 page 148 Transformers allow power utility companies to distribute large amounts or power at a reasonable cost. Large Transformers are used for power distribution along city streets and in large manufacturing or commercial buildings. These distributions are done both above and below ground locally and mostly overhead for long distances. The larger transformers are maintained by qualified workers specially trained in High Voltage Transformer Operation and Maintenance. Technicians will often work with small transformers. Control Transformers are used to isolate the power circuit from the control circuit, providing additional safety for the circuit operator or technician. Transformers are also used in power supplies of most electronic equipment to Step-Up or Step-Down the line voltage to provide the required operating voltage for the equipment.


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Energy Systems Engineering Technology Transformers have a Primary Winding and a Secondary Winding wound around an Iron Core as depicted in the below picture:

Figure 7-8 page 148 The Primary Winding is the coil that draws the power from its source and the Secondary Winding is the coil of the transformer that delivers the energy at the transformed or changed voltage. A Transformer Transfers AC Energy from one circuit to another. This transfer is made magnetically through the iron core as the magnetic field builds up around a wire when AC is passed through the wire. The magnetic field builds up and collapses each half cycle because the wire is carrying AC as depicted below:


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Energy Systems Engineering Technology The following picture also illustrates how Step-Up and Step-Down transformers change the voltage and current from the Primary Windings to the Secondary Windings as a ratio between the number of turns of the conductor in the Primary and Secondary sides of the transformer:

Figure 7-10 page 149 The advantage of increasing voltage and reducing current is that power may be transmitted through smaller gauge wire, thus reducing the cost of larger power lines. Although both voltage and current can be Stepped-Up or Stepped-Down, these terms when used with transformers, always apply to the Voltage.


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Energy Systems Engineering Technology The following picture depicts a High-Voltage Transmission Station where thousands of volts are received via overhead transmission lines and then transformed to a lower voltage for local distribution:

Picture page 150


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Energy Systems Engineering Technology SUMMARY:  

A TRANSFORMER is an electrical device that uses electromagnetism to change voltage from one level to another (the Voltage is Stepped Up or Stepped Down). TRANSFORMERS are used to increase voltage to a High Level for Transmission across the country and then to decrease that voltage to a Low Level for use to a variety of electrical loads (residential, commercial, and industrial).



KEO 3. 8.

EXPLAIN what TRANSFORMER LOSSES are and how they can be minimized.

Many TRANSFORMERS have a secondary coil that has an extra lead (tap) attached to it. A Tap is a connection brought out of a winding at a point between its endpoints to allow changing the voltage or current ratio. Although Transformers are very efficient, they are not perfect. Not all energy delivered to the primary side by the source is transferred to the secondary load circuit. There is a majority of energy lost as heat in the transformer. There are three types of TRANSFORMER LOSSES in an iron core transformer: Resistive Losses, Eddy Current Loses, and Hysteresis Losses. 

Resistive Losses come from the resistance of the coil winding. When current passes through the winding, the winding will heat up and lose energy that could have been transferred to the secondary. These losses are inherent and cannot be minimized.



Eddy Current Losses come because iron is a fair conductor of electricity. This is due to the varying magnetic field which induces a voltage in the secondary winding that also induces small voltages in the iron core of the transformer. The small voltages produce Eddy Currents, which in turn produce heat. This heat also represents a loss because it does not useful work. o Eddy Current Losses are minimized either by making the core of thin sheets (laminations) which are insulated from each other, or by powered-iron cores instead of solid blocks of iron. o The insulation between the laminations of a laminated core break up current paths within the core and reduces Eddy Currents. This same technique is used to


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Energy Systems Engineering Technology reduce Eddy Currents in Solenoids and was addressed in: Module # 2 Solenoids DC Generators and DC Motors. 

Hysteresis Loses occur each time the magnetizing force produced by the primary side of a transformer changes, the atoms of the core realign themselves in the direction of the force. This energy required to realign the iron atoms must be supplied by the input power and is not transferred to secondary load current. o Hysteresis Loses are minimized by using High Silicon Steel and other alloys in the construction of the core.

All three of these TRANSFORMER LOSSES make the typical iron core transformer hot when operating under full load. The transformer may be too hot to touch based on its size and load, but there should be no odor of burring insulation or varnish, or sings of discoloration or smoke. Any one of these conditions indicates the transformer is either overloaded or defective and service is necessary to correct and reduce damage, safety, or fire hazards.

SUMMARY:  

A


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EXPLAIN how SINGLE-PHASE and THREE PHASE TRANSFORMER CONNECTIONS are made to include both Primary and Secondary Taps.

SINGLE-PHASE CONNECTIONS utilize only one of the three phases of power distributed by the electrical utility. This Single Phase power is utilized throughout the world in residential applications and smaller businesses that do not require three phase power. The following picture depicts how Residential Electrical Power is provided by overhead 3-phase or lateral (underground) service as required by the National Electrical Code®:


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THREE-PHASE CONNECTIONS utilize all three phases of power in the same manner where each phase is Stepped-Down like it is with a single phase using three separate identical transformers. The following pictures depict: Transformer Secondary Tap, Centered-Tap, configurations to obtain a variety of different voltages:

Figure 7-12 page 152


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EXPLAIN what a CONTROL TRANSFORMER is and how they provide control voltage lower than the Primary Voltage applied.

A CONTROL TRANSFORMER is a transformer that is used to Step-Down the voltage to the control circuit for a system or machine. The most common Control Transformers have two primary coils and one secondary coil as illustrated in the following three pictures:




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Energy Systems Engineering Technology As depicted above, control voltage can be reduced from 480 VAC to 240 VAC and down to 120 VAC. Control Transformers are also designed to drop a control voltage down to 24 VAC as well, which is a much safer less hazardous voltage for technicians to work on and troubleshoot control circuits. In all cases the Stepped-Down voltage reduces the amount of voltage used to control a circuit operating on higher voltages. Transformer specification sheets are used to obtain required information when selecting the proper transformer for an application as depicted below:



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Picture Page 153 Control Transformers

Picture Page 154 Autotransformers AC Generators, Transformers, and AC Motors Module

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DESCRIBE two methods used to TROUBLESHOOT TRANSFORMERS.

Two methods used to TROUBLESHOOT TRANSFORMERS include: Measuring the Input and Output Voltages, and the Transformer Resistance. When transformers are installed into a circuit, they generally will operate without failure for a long time. This is because transformers have no moving parts. If a transformer does fail, it will appear as either a short circuit or an open circuit in one of its coils. 

Measuring Input and output voltages when a transformer is connected in a circuit it can be tested by measuring the input and output voltages. The transformer is considered good if the voltages are close to the transformers specifications. If a transformer voltage does not stay constant, current levels are tested when the transformer is loaded as it may not be holding up under its expected load.



Checking Transformer Resistance require the voltage to the transformer be removed from the primary windings (Locked-Out/Tagged-Out) and the secondary windings be disconnected. Using a DMM set to measure resistance to check for open circuits in coils, short circuits between coils, or coils shorted to the transformer core.

o To check for open circuits in coils, the resistance of each coil is checked. The winding is open and the transformer is bad if any coils show an infinite resistance reading. o To check for short circuits between primary and secondary coils, the resistance needs to be checked between primary and secondary coils. If an infinite resistance is not found between the primary and secondary coils, the coils have shorted and the transformer is bad. o To check for coils shorted to the transformer core, the resistance needs to be checked from each coil to the core. This check is good if the resistance is infinite. If there is a continuity reading from coil to core, the transformer is bad.


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Energy Systems Engineering Technology The following picture depicts how using a DMM can be used to test transformers:


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SUMMARY:  

L l

KEO 3. 12.

DESCRIBE what a SINGLE PHASE AC MOTOR consists of, its construction, and principle of operation to include advantages they have over DC MOTORS.

A SINGLE PHASE AC MOTOR is an AC motor that uses Alternating Current (AC) to produce rotation. The main parts of an AC motor are the Rotor, and a Stator. The Rotor is the rotating part of the motor and the Stator is the stationary part of an AC motor. A typical AC motor is used in industry because of their Simplicity, Ruggedness, and Reliability and can be Single Phase, Single Phase Two Speed Single Voltage, and Three Phase Single or Dual Voltage as depicted below also illustrating typical construction characteristics:


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Energy Systems Engineering Technology AC motors have several advantages over DC motors in that there are only two bearings that can wear, and there are No Brushes because the motor does not have a Commutator which reduces the need for extra maintenance associated with DC Motors. 

Single Phase Motors are commonly used in residential applications for AC Motor Driven appliances such as: Forced Air Furnace Fans, Air Conditioners, Washing Machines, etc. Single Phase Motors include: Shaded-Pole, Split-Phase, and Capacitor motors.

KEO 3. 13.



DESCRIBE three types of SINGLE PHASE AC MOTORS to include: ShadedPole, Split-Phase, and Capacitor motors.

Shaded-Pole motors are a Single Phase AC Motor that uses a shaded stator pose for starting the motor as depicted in the picture below:

[ Insert Figure 7-20 page 157 Rockis Book) ] AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology Shaded-Pole motors utilize the simplest method to start a Single Phase AC Motor. They are commonly rated at ½ horsepower or less and have low starting torque. Common applications include small cooling fans found in computers and home entertainment centers. The Shaded-Pole is normally a solid single turn of copper wire placed around a portion of the main pole laminations as indicated in the above picture. o This shaded pole delays the magnetic field in the area of the pole that is shaded. This shading causes the magnetic field at the pole area to be positioned approximately 900 from the magnetic field of the main Stator Field Pole. This movement determines the starting direction of a shaded pole motor. o A shaded-pole motor is a type of AC single-phase induction motor. It is basically a small squirrel cage motor in which the auxiliary winding is composed of a copper ring surrounding a portion of each pole. This auxiliary winding is called a shading coil. Currents in this coil delay the phase of magnetic flux in that part of the pole enough to provide a rotating magnetic field. The direction of rotation is from the unshaded side to the shaded (ring) side of the pole. The effect produces only a low starting torque compared to other classes of single-phase motors. o These motors only have one winding, no capacitor nor starting switch, making them economical and reliable. Because their starting torque is low they are best suited to driving fans or other loads that are easily started. Moreover, they are compatible with TRIAC-based variable-speed controls, which often are used with fans. They are built in power sizes up to about 1/6 hp or 125 watts output. For larger motors, other designs offer better characteristics. 

Split-Phase motors are Single Phase AC Motors that include a Running (main winding) and a Starting Winding (auxiliary winding). Split-Phase motors are AC motors of a fractional horsepower, usually 1/20 to 1/3 HP. They are commonly used to operate washing machines, oil burners, and small pumps and blowers. o A Split-Phase motor has a rotating part (rotor), a stationary part consisting of the running and starting winding (stator), and a centrifugal switch that is located inside the motor to disconnect the start winding at 60% to 80% of designed full speed.


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Energy Systems Engineering Technology o A Split-Phase motor is depicted in the below picture:


When the Split-Phase starts, both the Running and Start Windings are connected in parallel. The Start Winding is used to jump start the motor and then is disconnected by the centrifugal switch at 60% to 80% of full speed. When the motor is turned off, the centrifugal switch returns to its normally closed position (at approximately 40% of its full speed), ready to be used for starting the motor again.



A Capacitor Motor is also a Split-Phase AC Motor that includes a capacitor in addition to the running and starting windings. Capacitor Motors range in sizes ranging from 1/8 to 10 HP. Capacitor Motors are used to operate Refrigerators, Compressors, Washing Machines, and Air Conditioners.


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Energy Systems Engineering Technology o The Capacitor is wired in series with the Start Winding and provides a Capacitor Start Motor with the benefit of High Starting Torque. The Capacitor adds an extra jump start to get the motor to start with loads requiring High Starting Torque. A Capacitor Start Motor is depicted below:




A Capacitor-Run Motor is a Split-Phase AC Motor with the start winding and the capacitor connected in series at all times which does not have a centrifugal switch, giving this motor medium staring torque and somewhat higher running torque than a capacitor start motor as the capacitor continually charges and discharges while the motor is running.


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Energy Systems Engineering Technology o A Capacitor-Run Motor is depicted in the below picture:




A Capacitor Start-and-Run motor (used to run refrigerators and compressors) uses two capacitors with one used to start the motor, and the other one used as a capacitor to allow the motor to continue operating as a Capacitor Run Motor. This motor uses a larger capacitor to start the motor and a smaller one to run it.


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Energy Systems Engineering Technology o A Capacitor Start-and-Run motor depicted below with a centrifugal switch cutting out the start capacitor and allowing the run capacitor to stay in the start winding:

Figure 7-24 page 160 

A Capacitor Start-and-Run motor has the same starting torque as a capacitor start motor.



A Capacitor Start-and-Run motor has more running torque that a capacitorstart motor or a capacitor-run motor.

SUMMARY: 

.


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DESCRIBE what a THREE PHASE AC MOTOR is to include operational uses, and advantages they have over both DC Motors and AC SINGLE PHASE Motors.

THREE PHASE AC MOTORS are the most commonly used motors in industrial applications. Three Phase Ac Motors are used in applications ranging from fractional horsepower to over 500 HP. Three Phase Ac Motors are used in most applications because they are simple in construction, require little maintenance, and cost less to operate than Single Phase or DC Motors. The most common Three Phase Ac Motor is the Induction Motor. 

The Induction Motor is a motor that has three sets of Rotor Coils with each connected a different phase of the three phase power. These composite windings are the Phase A, B, and C of the three phase power. An Induction Three Phase Motor is illustrated below with different colors per phase in the Rotor and in the Voltage Sine Wave:


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Energy Systems Engineering Technology o Three Phase Motors are like having three single phase motors connected together to do more work more efficiently. Each phase is 1200 from the other phases and the magnetic field is produced in the stator because each phase reaches its peak magnetic strength 1200 from the other phases. They are self starting and do not require an additional starting method because of the rotating magnetic field in the motor. o Three Phase Motors are designed as either Single-Voltage Motors or Dual-Voltage Motors.


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

DESCRIBE SINGLE VOLTAGE and DUAL VOLTAGE THREE PHASE MOTOR applications to include WYE and DELTA Connections.

SINGLE VOLTAGE THREE PHASE MOTORS is a motor that operates at only one voltage level. They are less expensive to manufacture than Dual Voltage Motors, but are limited to locations having the same voltage as the motor. o Common Single Voltage Three Phase Motors ratings are 230, 460, and 575 VAC. Other ratings include 200, 208, and 220 VAC. o All Single Voltage Three Phase Motors are wired so that the phases are connected in either a (Y) or a (Δ) configuration as illustrated in the following two pictures:

Three Phase Wye-Connected Motor


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Energy Systems Engineering Technology o A Wye-Connected Motor has one end of each coil internally connected to the other phases.

Three Phase Delta-Connected Motor

Figure 7-27 page 163 o A Delta-Connected Motor has each phase coil wired end-to-end to form a completely closed loop. 

A DUAL VOLTAGE THREE PHASE MOTOR is manufactured so that they may be connected for either of two voltages. Making motors for two voltages enables the same motor to be used with two different three phase power supplies.


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Energy Systems Engineering Technology o The normal dual-voltage rating for three phase motors is 230/460 VAC. In either case the motor uses the same amount of power and gives the same horsepower output for either voltage, but as the voltage doubles from 230 VAC to 460 VAC, the current is cut in half. o Using a reduced current enables the use of a smaller gauge wire, thus reducing the cost of installation. Like Single Voltage motors, Dual Voltage motors can also be connected in either a (Y) or a (Δ) configuration as illustrated in the following two pictures:


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Energy Systems Engineering Technology Dual Voltage Three Phase Wye-Connected Motor

Figure 7-28 page 164 A Dual Voltage Wye-Connected Motor has each phase coil divided into two equal parts.


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Energy Systems Engineering Technology Three Phase Delta-Connected Motor

Figure 7-29 page 165 A Dual Voltage Delta-Connected Motor has each phase coil divided into two equal parts. KEO 3. 16.

DESCRIBE AC MOTOR TROUBLESHOOTING TECHNIQUES to include: Troubleshooting Single Phase Shaded-Pole, Split-Phase, and Capacitor Motors, and Three Phase Motors.

Most problems with AC Motors are related to Single Phase AC Motors dealing with the Centrifugal Switch, Thermal Switch, or Capacitors. These motors are usually serviced and repaired if the problem is related to the centrifugal switch, thermal switch, or capacitors. If a motor is less than 1/8 HP it is usually replaced as the cost to repair can exceed the replacement cost. As for Three Phase AC Motors, they usually operate for many years without any problems as they have fewer components that may malfunction than Single Phase AC or DC Motors. AC Motor Maintenance is extremely important and if maintained properly, many motor failures can be minimized or in some cases prevented. In general, electrical motors are very dependable and will provide good service under the conditions in which the motor was designed to operate within. To provide the safest service possible, a technician should check a motor name plate prior to putting it in service to ensure that the proper voltage and current are being used. The below picture depicts the type of information found on a motor’s name plate:


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Energy Systems Engineering Technology Any standard motor should not be operated in very damp locations or where water may enter the motor frame. There are specially designed motors for such locations with enclosures are available to totally enclose a motor from damp or wet locations. The frame of a motor should be grounded to prevent anyone receiving an electrical shock in the event the motor has developed a short. Motors in damp locations are at a greater risk of causing a shock hazard. The reason for grounding motors is that it is common practice for a technician to feel the motor to see if it has overheated and using a bare hand to feel a motor is done. Using a temperature indicating device or infrared temperature detector should also be used to check for a motor that may be overheated. To prevent an ordinary motor from becoming overheated, keep the air openings on its frame clear at all times. When oiling motor bearings, be sue not to use excessive oil as it could damage the motor winding resistance and could cause the motor to collect an excessive amount of dirt and dust. When inspecting or replacing a motor, a technician should ensure the enclosure meets the proper specifications as detailed in the below picture:


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Energy Systems Engineering Technology Figure 7-31 page 166 An open motor enclosure allows the air to flow through the motor to cool the windings to prevent overheating. A totally enclosed motor prevents air from entering the motor and cooling is provided by other means. If a motor does not start rotation after the switch has been turned ON, TURN OFF THE MOTOR and UNPLUG it to prevent any permanent damage to the motor’s windings from becoming overheated. The above methods discussed are preventive maintenance activities that a facility should have in place to keep its motors operating safely and efficiently. If done properly, all motors will provide longer service life and continue to operate efficiently.



Troubleshooting Shaded-Pole Single Phase AC Motors when they fail are usually replaced. The reason for the motor failure needs to be investigated to ensure the replacement motor not subject due to an overload situation or environmental conditions that may have caused its failure. To Troubleshoot a Shaded-Pole Motor the following picture illustrates a two step process:


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Energy Systems Engineering Technology Figure 7-32 page 167 To Troubleshoot a Shaded-Pole Single Phase AC Motor, the following procedure may be used: 1. Visually Inspect the motor after turning power off (lock-out and tag-out). a. Replace the motor if you see any discoloration showing it has been too hot. b. Replace the motor if the shaft if jammed or lock as the bearings have seized. c. Replace the motor if there is any sign of damage to the motor. 2. Check Stator Winding as it is the only electrical circuit that may be tested without taking the motor apart. a. Measure the resistance of the stator winding at the lowest DMM scale to verify an infinity reading. b. Replace the motor if the DMM indicates a zero reading (continuity) even though the winding may still be good. c. A final check can also be performed on the coil using a MEGOHMEETER to verify the coil does not break down with voltage applied. 

Troubleshooting Split-Phase Single Phase AC Motors generally looking at a thermal switch that automatically turns OFF the motor when it has overheated. These thermal switches may have a manual reset or an automatic reset when the motor has cooled down. Caution must be taken with any motor that has an automatic reset because the motor may automatically restart at any time. The following picture illustrates how to Troubleshoot Split-Phase Single Phase AC Motors:


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[ Insert Figure 7-33 page 168 Rockis Book) ] To Troubleshoot a Split-Phase AC Motor, the following procedure may be used: 1. Visually Inspect the motor after turning OFF the power (lock-out tag-out) a. Replace the motor if you see any discoloration showing it has been too hot. b. Replace the motor if the shaft if jammed or lock as the bearings have seized. c. Replace the motor if there is any sign of damage to the motor. 2. Check for Thermal Switch. a. With the motor power ON, check to see if a thermal switch exists, if it does, Reset the switch and turn the motor on if it is a manual reset switch. If it starts, observe it for normal operation.


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Energy Systems Engineering Technology 3. If it does not start, Check for voltage at the motor terminals using a DMM set to measure voltage. The voltage should be within 10% of the motor listed voltage. If voltage in not present or incorrect, continue troubleshooting the voltage problem. 4. If the motor voltage is good, turn OFF the motor (lock-out tag-out) to continue testing the motor. 5. With power removed, connect a DMM set to resistance to the same motor leads receiving the power (disconnect the motor leads from the incoming power leads to ensure accurate measurement of motor leads). A short circuit is present if the DMM reads Zero and an open circuit is present if the meter reads infinity. In either case, the motor will need to be replaced and in most cases they are normally too small for repair to be cost efficient. 6. Check for Centrifugal Switch if present look for signs of burning or broken springs. a. Service or replace the switch if any obvious signs of problems exist. b. Check the resistance of the switch. If the switch does not indicate it is open, manually operate the switch with the DMM still connected to verify proper operation (open and closed). To do this the end-bell on the switch may have to be removed. The resistance on the DMM decreases if the motor is good. If problem exists, the resistance will not change. 

Troubleshooting Capacitor Motors is similar to troubleshooting Split-Phase Motors. The only additional device to be tested is the Capacitor. Capacitors have a limited life and are often the problem with Capacitor Motors. They may develop short circuit internally, or become an open circuit. In either case they need to be tested and replaced as necessary and they eventually deteriorate to the point when then must be replaced. Deterioration may also change the value of a Capacitor, which will cause additional problems. When it shorts out, the winding in the motor could actually burn out and need to be replaced. When it deteriorates or opens, the motor will have poor starting torque, which can prevent the motor from starting or more often usually trips the motor overload devices (interlock switches). Capacitors designed to be connected to AC Power do not have an established polarity like in a DC Power circuit. The following picture illustrates the steps on how to troubleshoot a capacitor motor:


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Figure 7-34 page 169 To Troubleshoot Capacitor Single-Phase AC Motors, the following procedure may be used: 1. Lock-Out and Tag-Out the handle of the safety switch or combination starter in the OFF positon. 2. Measure the Voltage at the terminals to ensure the power is off (Zero Voltage Check) 3. Remove Cover from Capacitor which are usually located on the outside of the motor frame. CAUTION: A good capacitor will hold a charge even when the power is removed. 4. Visually Inspect Capacitor for any signs of leakage, cracks, or bulges. If any of these conditions are present, the capacitor will need to be replaced. AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology 5. Carefully Discharge the Capacitor if replacing by using a 20,000 Ὼ 5 Watt Resistor across the terminals of the capacitor for approximately 5 seconds. 6. After Capacitor has been discharged check its resistance with a DMM. The DMM indicates the general condition of a discharged capacitor. This test will verify if the Capacitor is good, shorted, or open.



a.

A good capacitor changes the reading of the DMM from Zero to Infinity. When the meter reaches the halfway point to Infinity, remove one of the meter leads and wait 30 seconds. When the meter is reconnected, it should return to the halfway point and continue to Infinity. This check verifies the capacitor can hold a charge provided by the DMM (in the Ohm range). If the capacitor cannot hold a charge, it will return back to Zero and it will need to be replaced.

b.

A Short Capacitor resistance reading changes to Zero and does not move. The capacitor is bad and needs replacing.

c.

An Open Capacitor resistance does not change from Infinity. If this is the case, the capacitor will need to be replaced.

Troubleshooting Three Phase AC Motors depends on the motor application. Testing is normally limited to checking the voltage at the motor if a motor us used in an application that is critical to an operation or production. Motors are assumed to be the problem if the voltage is not present and is incorrect. Unless the motor is very large, the motor is usually replaced so production may continue. Further tests on the removed motor or other motors not in critical operation may be made to determine the exact problem with the motor. The following picture illustrates steps to perform these tests to determine the motors fault:


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[ Insert Figure 7-35 page 170 Rockis Book) ]

To Troubleshoot a Three Phase motor, the following procedure may be used: 1. Measure Voltage at Motor Terminals to verify voltage if present and at the correct value on all three phases. If all the voltage is not present for all three phases, the power supply voltage must be checked and restored. If the voltage is present and correct but the motor will still not start, proceed to the next step. 2. Lock-Out and Tag-Out the incoming power to the motor and its controls per proper procedures. AC Generators, Transformers, and AC Motors Module

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Energy Systems Engineering Technology 3. Disconnect the Load from the Motor to see if the motor in not locked by the load. 4. Restore Power by removing the Lock-Out Tag-Out Tag per proper procedure and try restarting the motor. If the motor starts, the load needs to be checked for problems that have caused the motor not to rotate. If the motor does not start with the load removed, proceed to the next step. 5. Lock-Out and Tag-Out the incoming power to the motor and its controls per proper procedures. 6. Check the Motor Windings with DMM to measure resistance for any opens, or short circuits for all coils. This is can be a check across all coils, or to check indivudal coils, they will need to be isolated as indicated in the above picture illustrating how to Troubleshoot Three Phase Motors. a. If checking one coil first to determine its resistance, the basic laws of series and parallel circuits are applied for series or parallel connected coils. This can be used to check all coils together and if a problem exists, then each coil will have to be checked to determine where the problem may exist. TECHNICAL FACTS ON 3 PHASE MOTORS:


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STEP TWO AC Generators, Transformers, and AC Motors Skill/Performance Objectives

Skill Knowledge Introduction: Below are the skill knowledge objectives. How these objectives are performed depend on equipment and laboratory resources available. With each skill objective it is assumed that a set of standard test equipment and tools be provided and safety procedures be implemented during each tasked being performed.      

Inspect an AC Motor or Generator for proper operation and identify any defects on operation Evaluate the performance of a transformer to determine transformation efficiencies Disassemble and inspect an motor, transformer or generator and identify service needs Assemble a motor, transformer or generator replacing normal seals and wearing parts as specified in the technical manual Test a service motor to ensure safe and correct operation Perform a meggaohm test of a motor, generator or transformer and identify any faults indicated by the test results


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