Chapter 5 - Electrical Knowledge Flashcards
disruption of electrical supply
Interruption
measure of electric force or pressure. Analogous to pounds per square inch or kilopascals in a hydraulic system.
Volt (V)
Electromotive force
difference in electric energy between an energized conductor and another energized conductor, the ground, or other object.
Electrical potential (voltage)
a measure of current. One is the charge carried by 6.25x10(to the 18th) electrons moving past a given point in one second.
Ampere (amp, A)
the flow of electricity.
Current
a measure of electric power; one amp flowing at one volt. Calculated by multiplying volts and amps.
Watt (W)
one million watts
Megawatt
the ratio of voltage to current, measured in ohms. Analogous to friction or drag.
Resistance
measure of electrical resistance consisting of one volt flowing at one amp.
Ohms
the sum of resistance-inductive reactance and capacitive reactance.
Impedance
capacity of a material to transmit electricity.
Conductivity
electrical network consisting of a conductor or series of conductors through which electricity flows, including a return path to the source.
Circuit
interruption to the electrical supply.
Outage
amperages in a conductor that are larger than those for which it is rated.
Overcurrent
unintentional and undesirable conducting path or blockage of current in an electrical system.
Fault
current that is bypassing a designed conducting path.
Short circuit
fault that affects the dielectric properties of a system for an instant, and no longer exists after the power has been restored.
Transient fault
repeated momentary interruptions in the same place due to the same cause.
Intermittent fault
inrush of electricity caused when electrical devices, such as motors or transformers, are first switched on, at which time they can draw several times their normal operating electrical load; often occurs when circuits are first reenergized following an outage.
Current surge
electrification of a wire by passing it through a moving electromagnetic field.
Inductance
force field comprising electric and magnetic elements associated with electric charge in motion.
Electromagnetic field
in an electric utility system, a single primary energized conductor affixed to a pole or cross arm. Technically refers to the synchronized movement of electrical energy and pertains to common designs of electric supply lines, such as single (one primary conductor), two (two primary conductors), or three (three primary conductors).
Phase
system that automatically collects data and enables remote control switching operations.
Supervisory Control and Data Acquisition (SCADA)
electric facility equipped with transformers, switching equipment, and protection and control devices such as circuit breakers, automatic line reclosers, capacitors, or voltage regulators. Voltage is changed here.
Substation
region where transmission or extra-high transmission lines are connected. Allows utilities to transfer electricity both within their systems and among one another.
Transmission interconnect
the value (such as MW, Mvar, amperes, frequency, or volts) derived from, or a subset of the System Operating Limits, which if exceeded, could expose a widespread area of the Bulk Electric System to instability, uncontrolled separations or cascading outages.
Interconnection reliability operating limit (IROL)
electric facility that does not change voltage, but is used to route power through various circuits. May be strategically designed to compensate for portions of a system that are experiencing power failures, protecting circuits through disconnect switches, circuit breakers, relays, and communications systems.
Switchyard
high-voltage lines generally energized between 69 and 161 kV. They can be as low as 35 kV. Connect bulk transmission substations to industrial customers or distribution substations.
Subtransmission lines
in an electric utility system, the portion that delivers electricity to end-users. Includes distribution substations, primaries, distribution transformers, secondaries, and service lines.
Distribution network
in an electric utility system, electric supply lines usually energized between 2.4 and 23 kV
Distribution lines
in an electric distribution system, electric potential above a designated level, generally upstream of transformers.
Primary voltage
voltage leaving a transformer in the intended direction. On distribution systems in North America, is 120 to 240 volts.
Secondary voltage
stationary part of an electric generator. Contains field windings.
Stator
electric current that reverses its direction many times per second at regular intervals, typically used in power supplies.
Alternating current (AC)
graph of the changing intensity and direction of alternating current.
Sine wave
in electric generation, the number of cycles, or revolutions of spinning generation magnets, per second. Alternating current periodically varies in amplitude in conjunction with spinning generation magnets, intensifying from zero to a maximum value in a positive direction back to zero, and minimum value in the negative direction before returning to zero. The changing intensity and direction of alternating current is graphed in a sine wave. The time it takes for a magnet to complete a revolution is a cycle.
Hertz (Hz)
energized cable constructed from aluminum wire stranded around a steel core. Lightweight and relatively low-cost aluminum is often used as a conductor. However, it has a tendency to stretch when it heats, as it does when subject to high electric loads and elevated ambient temperatures. To minimize stretching and add strength, aluminum wire is stranded around a steel core in this cable construction.
Aluminum conductor steel reinforced (ACSR)
common return path for an electrical system.
Neutral wire
common return path for an electrical circuit or physical connection to the earth.
Ground wire
electric distribution configuration with three phases, but no common neutral wire. There is no fixed difference between phase-to-phase and phase-to-ground voltages.
Delta construction
in an electric utility system, a distribution secondary line that carries electricity from a transformer to a home or business.
Service drop
secondary wire, which has two insulated conductors and a neutral wrapped around a supportive cable. In North America, a single conductor typically carries 120 V, and the two together total 240 V.
Triplex
in an electric transmission or distribution system, the activation of a protective device.
Operation
wire connection between energized conductors and other electrical equipment, such as transformers.
Taps
permanent operation that requires manual closure of automatic line reclosers.
Lockout
transient fault in an electrical system, lasting from 33 to 133 milliseconds.
Momentary interruption
protective device mounted on distribution poles or crossarms that isolates line sections or protective zones in order to limit the number of customers who lose service as the result of a fault. They cut off current when an upstream recloser operates, isolating a fault in the line beyond it.
Line sectionalizer
device installed to protect electric facilities from voltage surges caused by sudden electrostatic discharges during electrical storms (lightning).
Lightning arrestor
material with poor conductivity— such as fiberglass, glass, polymers, and porcelain—used to separate energized conductors from poles or other objects or structures that must not be energized.
Insulator
electrical device that raises or lowers voltage through induction.
Transformer
device that increases voltage (e.g., from distribution to transmission).
Step-up transformer
device that reduces voltage (e.g., between primary distribution and secondary distribution).
Step-down transformer
electric flow in an unintended direction through a process whereby de-energized lines become energized from an external source, such as a home generator.
Back feed
ratio between the two wire coils in a transformer; identical to voltage ratio.
Turns ratio
the proportion of primary to secondary voltage of a transformer. It is identical to the turns ratio such that if the primary winding has 10 times the number of turns as the secondary coil, the turns ratio is 10 to 1; the voltage will be stepped down by a factor of 10.
Voltage ratio
electrical device that functions like an adjustable transformer, capable of either increasing or decreasing the circuit voltage.
Voltage regulator
a measure of the number of outages experienced by the average customer over a year’s time (or any specific time period): [total number of customer interruptions / total number of customers].
SAIFI (System Average Interruption Frequency Index)
a measure of the number of minutes the average customer is out of power over a year’s time (or any specific time period): [total duration of customer interruptions / total number of customers].
SAIDI (System Average Interruption Duration Index)
electrical potential over a specified distance. In the context of tree-caused electrical faults, it is determined by the voltage and spacing of the lines, as well as stem diameter and species of tree. Greater branch diameter and closer phase spacing create higher gradients. The higher the gradient, the more likely a tree is to cause a fault.
Voltage gradient
a series of power interruptions on a transmission system whereby one interruption increases vulnerabilities and causes additional interruptions, which in turn cause further interruptions, potentially resulting in widespread blackouts.
Cascading outage
not-for-profit international regulatory authority whose mission is to assure the reliability of the bulk power system in North America.
North American Electric Reliability Corporation (NERC)
Transmission Vegetation Management reliability standard for vegetation management along transmission lines, released by the North American Electric Reliability Corporation (NERC).
FAC-003
calculated minimum distance between conductors and vegetation to prevent spark-over, for various altitudes and operating voltages, that is used in the design of transmission facilities.
Minimum vegetation clearance distance (MVCD)
A / An __________ is a measure of electrical current.
amp
Voltage used by North American utilities generally ranges from _____ V for end users (customers) to _____ kV for the largest transmission lines.
120
765
A __________ is a blocked current or a bypass of an intended conducting path.
fault
Transmission lines terminate at __________, where voltages are changed using transformers to step up or step down the voltage in the lines.
substations
Primary distribution lines have lower __________ than transmission lines, which is safer and easier to work with.
voltage
Fiberglass, glass, polymers, and porcelain are good __________; aluminum and copper are good __________.
insulators
conductors
__________ is used on distribution lines in densely forested areas to provide some protection from faults caused by branches.
Tree wire
__________, the principal protective devices in distribution substations, are designed to operate in as little as 10 cycles.
Circuit breakers
Electrical flow in an unintended direction is called __________.
back feed
Three tree and electrical system characteristics that influence the likelihood of a tree-related service interruption are __________, __________, and __________.
voltage gradient
stem diameter
species
Two indices used to quantify reliability are SAIFI and SAIDI, which measure the __________ and __________ of interruptions experienced by the average customer over a given period.
frequency
duration
The most common cause of the tree-related service interruptions is __________ failure.
mechanical tear down
The utility system’s __________ allows the efficient transmission of electricity to areas of greatest need at a particular moment, which also makes the system more susceptible to __________.
interactivity
blackouts
The __________, or MVCD, is a calculated distance inside of which vegetation may not encroach.
minimum vegetation clearance distance
The capacity of a material to transmit electricity is referred to as
A) electrical fault
B) electromagnetic field
C) conductivity
D) inductance
C) conductivity
A transformer that is intended to reduce voltage is known as a
A) capacitor
B) step-down transformer
C) step-up transformer
D) voltage regulator
B) step-down transformer
Which of the following is not true of aluminum wire?
A) it is light weight
B) it is low cost
C) it has more conductivity than copper
D) it can span longer distances than copper
C) it has more conductivity than copper
Which of the following is true of guy wires?
A) they are intended for support, rather than electrical conduction
B) they are made of steel and are therefore conductive
C) they can become energized by direct or indirect contact with energized wire
D) all of the above
D) all of the above
True or false:
Electricity seeks the path of least resistance to the ground.
True
Transmission circuit breakers operate in response to all of the following irregularities, except
A) abnormally high amperage
B) abnormally high voltage
C) abnormally low voltage
D) unequal current
B) abnormally high voltage
