AC Fundamentals Flashcards
The amount of power that appears to be
present when voltage and current are measured on a feeder circuit.
The unit is the volt-ampere
Apparent Power
The ability of a capacitor to limit current
flow is known as
Capacitive Reactance
The voltage induced in an inductor
by its own magnetic field.
Counter Electromotive Force
Coil connections where the opposite ends of the three
coils are connected together
DELTA
The number of times a generator rotates in one
second.
Frequency
the unit of measure for frequency, just as volts
is the unit of measure for electrical pressure.
Hertz (Hz)
the ability of a conductor to oppose a
change in current.
Inductance
The current limiting property of an inductor.
Inductive Reactance
a device that uses the electrical energy of the
source to accomplish some useful purpose.
Load
The use of a constantly changing magnetic
field in one conductor to produce a voltage in another conductor.
Mutual Induction
The interruption of the complete path needed for
current to flow in a circuit. A broken phase or neutral can cause this
Open Circuit
A circuit that has multiple paths for current to
flow.
Parallel Circuit
The order in which the three phases are labeled
for rotation purposes.
Phase Sequence
refers to how reactance (both capacitive
and inductive) causes voltage and current to be out of phase with
each other.
Phase Shift
An electrical instrument used to prove phase
sequence over open points on high voltage lines.
Phasing Meter
the relationship between true
power and apparent power and can range from 0% (zero) to 100%.
100% means that all of the power produced in a
system is available for use.
Power Factor
an acronym for root means square and is a value of
AC voltage that will produce the same amount of power as a like
value of DC voltage.
RMS
portion of a three-phase motor it is
mounted to the shaft of the electric motor.
Rotor
A small voltage induced in a conductor when an
AC current is applied to that conductor. The small induced voltage
has a polarity opposite to the applied voltage.
Self Induction
A circuit that has one path for current to flow.
Series Circuit
A circuit that does not have a load, or in which the
load has been bypassed.
Short Circuit
A graphical representation of what is happening to
voltage in an AC circuit over a period of time.
Sine Wave
The stationary portion of a three-phase motor. They are energized by each phase of the source, which produces a
rotating magnetic field and causes the rotor to rotate.
Stator
The amount of power used in a circuit when phase
shift is accounted for. will always be equal to or less
than apparent power.
True Power
A value used to measure reactive power in a pure inductive
circuit.
VARs
Coil connections where the single like ends of the three coils
are connected together. This connection is also referred to as a star
connection
WYE
Explain Basic Circuits
Electrical circuits require a source, a complete
conductive path, and a load. If the conductive path is broken, an open
circuit results. If the load is bypassed, a short circuit occurs. There are
two basic types of circuits. A series circuit has only one path for current
to flow, while a parallel circuit has more than one path for current to
flow.
Explain Capacitors
A capacitor is a device that stores electrical energy
in an AC circuit. Capacitors are used for power factor correction
to counteract inductance, which is caused by inductive loads
(transformers and motors). It can be said that capacitance is the
opposite of inductance. Without capacitors, the power factor would
fall, which would result in dim lights and substantial losses for the
utility company.
Explain Generation Process
Rotating a magnetic field near coiled
conductors generates AC power. This principle is based upon the law
of charges. The magnet is charged, and as it passes near the coiled
conductor, the electrons in that coiled conductor are repelled. As the
magnet rotates, the electrons are repelled from one end of the magnet
and then attracted by the opposite end. The electrons are said to be
alternating in direction, thus the term alternating current.
Explain Induction
When current is applied to a conductor, a magnetic field
is produced. If the conductor is connected to a source of AC, the
magnetic field is expanding and collapsing as the current alternates. It
has been observed that when a second conductor is placed within the
expanding and collapsing magnetic field that a voltage will be picked
up (or induced) in the second conductor.
Explain Parallel Principles
The overall power system can be broken down
into several parallel circuits. Transmission lines exiting a generating
facility are at the same voltage. Each of these lines is parallel to the
others, meaning that each line has its own path to and from the
substation. If one transmission line goes down, the other lines should
be unaffected.
Explain Power Factor
Power factor is a way of indicating that portion of the
total current and voltage that is producing power. If the voltage and
current sine wave are in unison, the power factor is 100%, which is
preferred. Inductors will cause the current sine wave to lag the voltage
sine wave, which reduces the power factor. Capacitors will cause
the current sine wave to lead the voltage sine wave; therefore, if an
amount of capacitance is added to a line that is equal to the amount
of inductance, the current sine wave will be in unison with the voltage
sine wave. A 50% power factor means that only 50% of the power
produced is available for use, while a 100% power factor means that all
of the power that is being produced is available for use by consumers.
Utilities always strive for a 100% power factor.
