AC Power Sources 281

AC

Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC is supplied to homes and businesses by electrical distribution systems.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current is supplied to homes and businesses by electrical distribution systems.

amperage

A measurement of the amount of current flowing in a circuit. Amperage is measured in amperes (A).

armature

The component of a generator in which current is induced. The armature usually consists of a series of coils or groups of conductors surrounding a core of iron.

armature core

The part of the armature that supports the windings to provide a path for magnetic flux. Armature cores are typically made of laminated iron or steel.

armature windings

A conducting coil that is wound around the armature in which voltage is induced. Armature windings move through the magnetic field, inducing voltage in the windings.

balance loads

Three-phase power in which current is evenly distributed across all three phases. Balanced loads can improve the efficiency of generators, provide stable voltage, and achieve better system performance.

bridge rectifiers

A type of full-wave rectifier with four diodes. Bridge rectifiers convert both the positive and negative cycles of AC to DC.

brushes

A component in generators that transfers electrical current between the stationary and rotating parts of the generator. Brushes are typically made of carbon or graphite.

capacity

A generator's ability to handle and produce voltage current. Power capacity for generators is measured in watts (W).

center-tapped rectifiers

A type of full-wave rectifier that combines a center-tapped transformer with two diodes to convert AC to DC. Center-tapped rectifiers are used in some telecommunication systems and three wire power distribution.

circuit breakers

A safety device that detects and disables excess current in a circuit to prevent overheating. Circuit breakers often contain a bimetallic strip that bends and trips a switch that opens a circuit.

coils

A length of conducting wire in which a voltage is induced. Coils typically contain many turns, or loops, of wire.

conductor

A material or element that allows free movement of electrons and therefore allows electricity to flow easily. Conductors are typically copper and aluminum.

copper loss

A decrease in amperage caused by the resistance that current encounters when flowing through a conductor. Copper loss is reduced in AC systems.

core-type transformer

A type of transformer which has all of its limbs wrapped with windings. Core-type transformers are used for power distribution.

current

The flow of electricity. Current strength is called amperage and is measured in amperes (A).

cycles

The process of alternating current going from zero to its peak value, back to zero, then to its peak negative value and back to zero. One complete AC cycle equals 360 electrical degrees.

DC

Direct current. Electricity that travels in one direction. Direct current is often used for devices, but alternating current is used for the electric grid.

delta

Δ. A connection of three conductors that forms a triangular series circuit. Delta connections are used in three-phase power systems for high-power applications.

delta/delta

Δ-Δ. A three-phase transformer with delta connections for both the primary and secondary winding. Delta/delta connections are one of the most common connections for step up transformers in generating stations.

delta/wye

Δ-Y. A three-phase transformer with a delta primary winding and a wye secondary winding. Delta/wye connections are used in both step up and step down transformers.

dielectric boots

A type of insulating rubber footwear that protects the feet and lower legs from electric shock. Dielectric boots may be worn by themselves or over other footwear.

direct current

DC. Electricity that travels in one direction. Direct current is often used for devices, but alternating current is used for the electric grid.

distribution substation

A bank of step-down transformers located near the end users of a distribution system. Distribution substations transform voltage closer to the lower levels that end users require.

distribution systems

A group of electrical components that provides electricity from a generating station to specific end destinations. Distribution systems, such as transformers, power lines, and substations, transmit electricity to buildings and other structures.

electric shock

The flow of electricity through the body. Severe electric shock can be fatal.

electrical boxes

A metal cabinet in a building where power from the electrical distribution system enters and is distributed throughout the building. The electrical box connects to every circuit and device in the building.

electrical degrees

A unit of measurement for expressing the amount of rotation in a generator. One electrical degree represents 1/360th of a full cycle of an alternating current waveform.

electrical energy

Energy created by the movement of electrons. Electrical energy can be converted into light, heat, or motion.

electrical fires

A fire involving energized electrical equipment. Electrical fires are very dangerous because they put technicians at risk of electric shock and burns.

electromagnets

A magnet that gains an attractive force only when current passes through it. An electromagnet is typically formed by wrapping a current-carrying coil around a pole piece.

electrons

A negatively charged particle that orbits the nucleus of an atom. Electrons flowing between atoms causes electricity.

enclosure

A closed-off area or container that surrounds electrical devices and circuits. Enclosures provide mechanical and/or electrical protection to components such as transformers.

excitation current

The energy supplied to the electromagnets to create a magnetic field in a generator. Excitation current is produced by an exciter.

exciter

An AC generator that is used with another generator or motor to provide excitation current. Exciters also help stabilize voltage.

field windings

A coil of conducting wire connected to the armature that energizes the pole pieces. Field windings are connected to a stationary armature in a rotating field generator.

filters

A device that diminishes the ripple present in rectified AC. Filters keep rectified voltage as close to peak value as possible.

flame-resistant

FR. A type of clothing that ignites but stops burning when the ignition source is removed. Flame-resistant clothing limits the injuries that wearers may sustain from electrical fires.

frequency

The number of complete alternating current cycles completed in one second. Frequency is measured in hertz (Hz).

full-wave rectifier

A rectifier that converts a complete AC cycle to DC. Full-wave rectifiers are more common than half-wave rectifiers because they are more efficient.

generating stations

A facility that houses multiple large, linked AC generators. Generating stations produce large amounts of power for distribution systems.

generators

A device that converts mechanical energy into electrical energy. Generators operate on the principle of magnetic induction and create alternating current.

grounding

A means of providing a safe alternate path for current in case it strays from its intended path. Grounding reduces safety risks and ensures equipment runs smoothly.

half-cycle

An incomplete cycle of AC that goes from zero to either peak value. A half-cycle of AC is equal to 180 electrical degrees.

half-wave rectifier

A rectifier that converts AC to DC during either the positive or negative half of the AC cycle, but not both. Half-wave rectifiers are less efficient and need more filtering than full-wave rectifiers.

hard hats

A lightweight, protective head covering, usually made of plastic, used to protect the head from impacts, bumps, and electric shock. Hard hats have a shock-absorbing lining with a headband and straps that suspend the shell away from the skull and provide ventilation.

hertz

Hz. A unit of measurement equal to one cycle per second. Hertz are used to measure frequency.

in-phase

The condition in which multiple generators have voltage waveforms that peak at the same time. In-phase generators have the same frequency and phase angle.

insulated gloves

A protective hand covering made of insulating rubber that reduces the risk of injury and electric shock. Insulated gloves protect electricians when working on live wires or electrical equipment.

interconnected system

A distribution system with multiple parallel power sources located throughout the system. Interconnected systems, also known as network systems, guarantee uninterrupted power because other power sources can be used if one goes down.

iron

A malleable, silver-white metal that is highly magnetic. Iron is used to create pole pieces.

kilovolt-amperes

kVA. A unit of measurement that is equal to voltage multiplied by amperage. Kilovolt-amperes are used to rate transformer and generator strength.

kilovolts

kV. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. One kilovolt is equal to 1,000 volts.

kVA

Kilovolt-amperes. A unit of measurement that is equal to voltage multiplied by amperage. The unit kVA is used to rate transformer and generator strength.

laminated

Thin sheets of magnetic metal that are sealed together in multiple layers. Laminated metals help to reduce resistance losses.

limbs

A column of a transformer core which may have windings wrapped around it. Limbs may be designed differently for different types of transformers.

lines of flux

An imaginary line of force that surrounds a magnet. Lines of flux form a magnetic field.

load

A component in a circuit that converts electrical energy into light, heat, or mechanical motion. Examples of loads are light bulbs, appliances, and machines.

lockout/tagout

A method of protecting employees from accidental machine startup through proper locking and labeling of machines. Lockout/tagout is an essential practice for safe repair of machines.

loop system

A distribution system that provides multiple paths from one or more generating stations to end users that form a loop. Loop systems are more reliable than radial systems because power can be supplied from two directions.

magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the forces of attraction and repulsion.

magnetic flux

The force that surrounds a magnet and exhibits the forces of attraction and repulsion. Magnetic flux is described as imaginary lines of force that exit the magnet's north pole and return to its south pole.

magnetic induction

The use of magnets to produce voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.

magnets

A metallic object or substance that possesses a force that attracts or repels other metals. Magnets attract opposite charges and repel like charges.

mechanical energy

Energy produced by a force or motion. Mechanical energy is converted into electrical energy in a generator.

multimeter

A device that combines the functions of an ammeter, a voltmeter, and an ohmmeter. Multimeters can detect remaining energy in a machine after attempting to de-energize it.

mutual induction

The process of one coil inducing a voltage in another coil without an electrical connection. Mutual induction is used in transformers to step up or step down voltage.

negative charge

An electrical charge with a surplus of electrons. A magnet's north pole carries a negative charge.

network system

A distribution system with multiple parallel power sources located throughout the system. Network systems, also known as interconnected systems, guarantee uninterrupted power because other power sources can be used if one goes down.

north pole

The negative side of a magnet. Lines of flux exit the north pole and are attracted back to the south pole.

out-of-phase

A condition that occurs when waves reach their peak positive and peak negative values at a different time. Out-of-phase waves occur in a three-phase generator.

output voltage

The amount of electrical pressure or potential that is produced by a power source. The output voltage of a generator depends on the number of flux lines cut per second.

parallel circuits

An electrical system that has multiple paths for the flow of electricity. Parallel circuits allow individual loads and paths to operate independently of one another.

peak negative value

The lowest negative point on a wave. Peak negative value is equal to the maximum negative voltage or amperage of the wave.

peak positive value

The highest positive point on a wave. Peak positive value is equal to the highest voltage or amperage of the wave.

peak value

The maximum positive or negative value of an alternating current wave's voltage or amperage. Peak values are important for various waveform calculations.

personal protective equipment

PPE. Any of the various devices that employees wear to prevent injury or illness. Common personal protective equipment worn during electrical work includes safety glasses, rubber-soled footwear, and gloves.

phase

The timing or position of an alternating current voltage or amperage wave relative to a reference point or other waveforms. The phase difference in a three-phase generator allows for continuous, balanced power.

PN diodes

A semi-conductor diode that has one positively charged side and one negatively charged side. PN diodes allow current to flow only from the negative side to the positive side.

polarity

The state of having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.

pole pieces

A metallic object mounted on the stator or rotor of a generator that creates and directs the magnetic field. Pole pieces form the electromagnets that create lines of flux when connected to the field windings.

positive charge

An electrical charge with a shortage of electrons. A magnet's south pole carries a positive charge.

power

The amount of work accomplished within a given period of time. Power is the product of amperage and voltage and is measured in watts (W).

power sources

A device that generates electricity. Power sources include generators and batteries.

power supply

A device that contains transformers, rectifiers, and filters and provides electrical power to a load. Power supplies also convert voltage to the desired input, convert AC to DC, smooth out the fluctuated voltage, and regulate output voltage.

primary winding

The first winding that current passes through in a transformer. Primary windings bring in the electricity supplied to the transformer.

prime mover

A device that supplies the turning force necessary to turn the shaft of a generator. Prime movers for AC generators include steam turbines and diesel engines.

radial system

A distribution system with a single generating station that provides only one path to end users. In a radial system, the entire system loses power if the power source goes down.

rectifiers

A device used in an electrical circuit to convert AC to DC. Rectifiers use diodes to prevent current from flowing in more than one direction.

reserve generator

A generator that is activated when the primary power source cannot generate enough voltage to meet demand. Reserve generators are linked in parallel to other generators.

resistance

R. The opposition to current flow. Resistance is measured in ohms (O).

ripple

A fluctuating voltage pattern. Ripples in AC make it unsuitable for most electronic devices.

rotating armature generator

A device that generates alternating current by rotating an armature through a stationary magnetic field. Rotating armature generators cannot output as much voltage as rotating field generators, making rotating armature generators less common.

rotating field coil

The electromagnet that is wound around the rotor of a rotating field generator. Rotating field coils produce a magnetic field.

rotating field generator

A device that generates alternating current by rotating a magnetic field within a stationary armature. Rotating field generators are the most commonly used type of AC generator.

rotor

The rotating component of a motor or generator. A prime mover powers the rotor.

secondary winding

The second winding that current passes through in a transformer. Secondary windings output electricity.

series circuit

An electrical system that has only one path for the flow of electricity. Series circuits are formed in a delta connection for three-phase generator armature windings.

shell-type transformer

A type of transformer that contains non-wrapped paths on either side of the limbs. Shell-type transformers are used for industrial applications.

sine waves

An alternating current waveform that forms semi-circular curves. Sine waves, also known as sinusoidal waves, are produced by alternators and alternating current generators.

single-phase

1Φ. Alternating current power that consists of only one voltage wave. Single-phase power is typically used for simple applications like lighting and heating.

single-phase generator

An alternating current generator that produces a single voltage wave per phase. Single-phase generators produce smaller amounts of voltage, so they are used in low-power electrical systems.

single-phase transformers

A transformer with only one or two limbs and two windings. Single-phase transformers work best for low-power requirements.

slip rings

A conductive device attached to the end of a generator rotor that conducts current from the rotor to the external circuit. Slip rings require regular maintenance because continuous friction wears them down.

south pole

The positive side of a magnet. Lines of flux enter the south pole after exiting the north pole.

spikes

A sharp, sudden increase in voltage in a circuit that can damage equipment. Spikes can be caused by malfunctions and changing load conditions.

stator

The stationary component of a motor or generator. Stators function differently depending on the type of generator.

step down

Transform to a lower voltage. To step down voltage, a transformer's primary winding must have more turns than its secondary winding.

step up

Transform to a higher voltage. To step up voltage, a transformer's primary winding must have fewer turns than its secondary winding.

step-down substations

A grouping of transformers that step down voltage at different points in the electric grid. Step-down substations are a source of subtransmission lines.

step-down transformer

An electrical device that reduces the voltage of alternating current. Step-down transformers convert high voltage from the primary winding into low voltage in the secondary winding.

step-up substations

A grouping of step-up transformers that receive electricity from a nearby generating facility to increase the voltage for transmission to distant locations. Step-up substations require large power transformers and grounding.

step-up transformer

An electrical device that increases the voltage of alternating current. Step-up transformers convert low voltage from the primary winding into high voltage in the secondary winding.

synchronized

Controlled to operate in exact unison. Generators are considered synchronized if they have identical voltage, frequency, and phase rotation.

three-phase

3Φ. Alternating current power that consists of three overlapping waves. Three-phase power is used for all large AC motors and is the standard power supply for factories and industrial buildings.

three-phase generator

An alternating current generator that produces three voltage waves for each 360-degree phase. Three-phase generators contain three sets of armature windings that are offset by 120 electrical degrees.

three-phase transformers

A transformer that contains three limbs with their own primary and secondary windings. Three-phase transformers are used for high-power applications.

transformed

Increased or decreased in voltage. There is no effective way to transform DC.

transformer core

A magnetic component of a transformer that provides a low-resistance path for magnetic flux. Transformer cores are made of laminated iron or steel.

transformers

A device that uses mutual induction to transfer electrical energy from one circuit to another without changing the frequency. Transformers are most often used to increase and decrease voltage.

turbine

A machine with at least one moving part that converts mechanical energy into electrical energy. Turbines may provide the mechanical energy necessary to rotate a rotor in a generator.

turns

One loop or wrap of conducting wire in a coil. The number of turns in an armature coil affects generator output voltage.

turns ratio

The relationship between the number of turns in the primary and secondary windings of a transformer. Transformers step up or step down voltage based on the turns ratio.

voltage

A measure of electrical pressure or potential known as electromotive force. Voltage is measured in volts (V).

voltage regulation

The process of controlling the fluctuation of AC voltage. Voltage regulation ensures voltage stays at a constant level.

wye

Y. A connection of three conductors in which one end of each conductor is connected to a common, neutral point. Wye connections are used in three-phase power systems when balanced loads and grounding are necessary.

wye/delta

Y-Δ. A three-phase transformer with a wye primary winding and a delta secondary winding. Wye/delta connections are generally used for stepping down voltage in certain industrial applications.

wye/wye

Y-Y. A three-phase transformer with wye connections for both the primary and secondary windings. Wye/wye connections offer a safer connection for step up transformers because they are grounded.