Download AC Generation – Vocabulary Terms

AC Generation
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.
AC Generation
Vocabulary Term
Definition
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 halfwave 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.
AC Generation
Vocabulary Term
Definition
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.
AC Generation
Vocabulary Term
Definition
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. Threephase 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.