AC Power Sources 235

This course introduces the various means by which AC power is produced and used. It also covers AC’s advantages over DC and power transformation. Includes an Interactive Lab.

Class Details

Class Name:
AC Power Sources 235
This course introduces the various means by which AC power is produced and used. It also covers AC’s advantages over DC and power transformation. Includes an Interactive Lab.
Number of Lessons:
Additional Language:
Related 2.0 Class:
AC Power Sources 281

Class Outline

  • Objectives
  • What Is AC Power?
  • AC Generator Principles
  • Generator Motion
  • Revolving Field Generators
  • AC Generator Parts
  • Generator Connections
  • AC Generator Frequency
  • AC Generator Power Output
  • Parallel Generator Connection
  • Generator Synchronization
  • Voltage Transformers
  • Types of Transformer Cores
  • Transformer Connections
  • Distribution Systems
  • Power Transmission
  • Rectifying Process
  • AC Power Safety
  • Summary


  • Describe the characteristics of AC power.
  • Describe how generators use magnetic induction.
  • Describe the motion of revolving armature generators.
  • Describe the main type of AC generator.
  • Describe the parts of revolving field AC generators.
  • Distinguish between single and three-phase power.
  • Describe generator frequency.
  • Describe factors that affect generator output.
  • Explain parallel generator connection.
  • Describe how AC generators are synchronized.
  • Describe voltage transformers.
  • Describe the basic types of transformer cores.
  • Describe transformer connections.
  • Describe common power distribution systems.
  • Describe how AC power is transmitted.
  • Describe the process of converting AC to DC.
  • Describe ways to reduce electrical safety risks.


  • MSSC Maintenance Awareness


Vocabulary Term Definition
adapter A device that converts AC to DC. Adapters take the AC from a wall outlet and convert it to the DC that electronic devices need.
alternating current Current that regularly reverses the direction of its flow in a repeating, cyclical pattern. AC is the dominant form of power because it can be transformed and transported over long distances.
alternator Another word for an AC generator, especially when referring to a car. An alternator converts mechanical energy into alternating current electrical energy.
armature The part of a generator in which a current is induced by a magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.
bridge rectifier A type of full-wave rectifier with four diodes that converts both the positive and negative cycles of AC voltage to DC.
brushes Sliding electrical contacts used to provide a connection between the armature and the external circuit.
brushless exciter An AC generator design that mounts a small DC generator on its shaft, which when rotated provides the direct current to excite the magnetic field.
center tap A wire connected to the midpoint of a transformer secondary winding. This allows the transformer to use different turns ratios.
coil The loop of conducting wire wrapped around the armature. Each additional armature coil is on a different axis, to produce smoother output voltage.
commutator The rotating switch attached to the brushes of a DC generator. The commutator maintains DC when the rotation of the armature switches the polarity of the conductor.
copper loss A power loss due to current flowing through wire. Copper loss is proportional to the resistance of the wire and the square of the current.
core A component of a transformer. The iron or steel core provides a controlled path for the magnetic flux generated in the transformer by the current flowing through the windings.
delta A connection of three components where a triangular series circuit is formed. Delta connections are used in three-phase power systems.
delta/delta A transformer with both the primary and the secondary connected as a delta.
delta/wye A transformer with the primary connected as a delta and the secondary connected as a wye.
diode A two-terminal semiconductor device that allows current to flow through it in only one direction. A diode has a low resistance in one direction and a high resistance in the other direction.
distribution substation A bank of step down transformers near the end users. The distribution substation converts voltage closer to the required usable levels.
distribution system A circuit of users linked to a generating station. Most distribution systems are either radial or interconnected.
efficient Having an energy output that is close to the total energy supplied. An efficient system has very little resistance loss.
electromagnetic induction The process in which voltage is induced in a magnetic field using a current-carrying coil. AC generators and transformers use electromagnetic induction.
electromotive force Electrical pressure, abbreviated emf. It is the force that pushes electrons through a conductor, measured in volts.
enclosure A mechanical or electrical protection for components used in a system.
excitation current The DC required to magnetize a piece of metal.
Faraday's Law A law that states an electric field is induced in any system in which a magnetic field is changing with time.
filtered Removing the ripple effect caused by a rectifier.
flux leakage The amount of flux lines that do not follow the core and are lost to the surrounding air.
frequency A measurement of the number of complete AC cycles that occur in one second. Frequency is measured in hertz.
full-wave rectifier A rectifier that flattens both positive and negative halves of the incoming AC to pulsating DC. This design is used more often because it is more efficient than a half-wave rectifier.
generating station A building where utility companies house large, linked AC generators to create the massive power for widespread use.
generator A device that converts mechanical energy into electrical energy by magnetic induction.
H type core A type of transformer core that surrounds the windings on four sides. This helps lessen flux leakage.
half-wave rectifier A rectifier that flattens only the positive or negative half of the incoming AC to pulsating DC. This is less efficent and needs more filtering than a full-wave rectifier.
hertz The unit used to measure frequency. Hertz expresses the number of complete AC cycles per second.
hollow core A type of transformer core where the windings surround the laminated iron core.
hydroelectric Electricity produced by turbines that are turned by water flow.
interconnected system A distribution system with multiple available power sources that can loop throughout the network. If one source goes down, a different source can be activated to maintain service.
kilovolt-amps Units used to rate transformer and generator strength. A kilovolt is a thousand volts.
laminated Thin sheets of metal sealed together to construct the core for transformers. Lamination helps reduce resistance losses.
lockout/tagout A method of protecting employees from accidental machine startup through proper locking and labeling of machines that are undergoing maintenance.
magnetic flux A measure of the strength of the field formed around a magnet. Flux is expressed in webers (Wb).
magnetic induction The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.
mutual induction The ability of one coil to induce a voltage into another coil. This principle is used in transformers.
network system A distribution system where multiple power sources are connected to each user to guarantee uninterrupted power. A network system is expensive, so it is only used when constant power is vital.
open delta A transformer connection that does not complete the triangle, using only two of the three sides. An open delta is used when full power is not needed.
polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.
pole Either of two oppositely charged ends of a magnet. It is the relationship of the poles that cause magnetic flux.
pole pieces Devices mounted on the inside of a generator armature. When connected to field windings, the pole pieces form the electromagnets that create lines of flux.
primary winding Turns of wire on a transformer core used to transfer voltage from the input to the core.
prime mover A device supplying the turning force necessary to turn the shaft of a generator or alternator. Steam turbines or diesel engines are the most common prime movers for AC generators.
radial system A distribution system with only one power source. If that source goes out, power is lost to the entire circuit.
rectified AC that has been flattened by a diode to change it to DC.
regulated Controlled, so that voltage is maintained at a constant level.
revolving armature generator A setup where the conductor wound armature is rotated between an electromagnetic field. AC generators rarely use this design.
revolving field generator A setup where an electromagnetic field is rotated between the conductor wound armature. Most AC generators are of this design.
ripple Characterized by a varying value. Unlike the constant values of DC, the average value of an AC output constantly ripples.
rotor The rotating part of an alternating current generator.
secondary winding Turns of wire on a transformer core used to transfer voltage from the core to the outside load.
shell core A type of core that surrounds the windings.
sine wave The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.
single-phase A continuous single alternating current cycle.
slip ring A conductive device attached to the end of a generator rotor that conducts current to the brushes.
spike A sharp, sudden increase in voltage in a circuit caused by malfuction or changing load conditions that can damage equipment.
stator The stationary windings of an alternating current generator.
step down In electricity, a phrase used to describe voltage adjustment. To step down voltage means to decrease voltage.
step up In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage.
synchronized Meeting the necessary conditions to operate in exact unison. Generators are considered synchronized if they have identical voltage, frequency, and phase rotation.
terminal A connecting point in a circuit where a wire is attached to create an electrical connection.
three-phase A continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large scale distribution systems.
toroid core A donut shaped electromagnetic transformer core. The toroid is very efficient because it minimizes flux leakage.
transformer A device that transfers electrical energy from one circuit to another, without changing the frequency, using electromagnetic induction. A transformer is most often used to change the line voltage.
transmission substation A bank of step up transformers near the generating station. Transmission substations increase voltage to as high as 800kV for widespread distribution.
turbine A machine that uses the motion or energy of moving water or wind to produce movement in paddles, buckets, or other devices arranged in a circle. This mechanical motion is converted to electricity.
turns ratio A comparison of the number of turns in the primary versus the number of turns in the secondary in a transformer.
weber A unit used to express flux density. One weber (Wb) is equal to 100 million lines of flux.
winding The conducting coils that are wound around the armature in which voltage is induced if moved within a magnetic field. Also used to transfer voltage in transformers.
wye A connection of three components where one end of each component is connected at a common point. Wye connections are used in three-phase power systems.
wye/delta A transformer with the primary connected as a wye and the secondary connected as a delta.
wye/wye A transformer with both the primary and the secondary connected as a wye.