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Volt
A measure of electrical force, it is also called electromotive force
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Voltage used by North American utilities generally ranges from ___ V for end users(customers) to ____kV for the largest transmission lines
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Electric potential
Difference in electric energy between an energized conductor and another energized conductor, the ground, or other object
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Watt
A measure of electric power
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One watt is one____ flowing at _____
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Watts are calculated by -
- Multiplying volts and amps.
- I X V = W
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One horsepower is equal to _
One and one third watts
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Consumer use of electricity is measured in
Kilowatt hours
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How to calculate kilowatt hours
(Watts used X hours) / 1000
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Megawatt
A million watts. Power plants generate hundreds of megawatts
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Resistance
Opposition to current flow
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Resistance is measured in
Ohms
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Ohm is ___volt flowing at ____
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Impedance
The sum of resistance-inductive resistance and capacitive resistance
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Conductivity
The capacity of a material to transmit electricity.
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Materials with high conductivity have ____ resistance to electricity, while poor conductors have____ resistance
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Good conductors often used for wires
Aluminum and copper
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Poor conductors that make good insulators
Fiberglass, glass, polymers, porcelain
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Electrical current completes a circle or ____ to and from its couse
Circuit
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The return path in a circuit may be ___
A neutral, ground or other energized wire
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A break in the circuit ———
Stops the flow of current
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In North America some utilities also refer to distribution circuits as
Feeders
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A power outage is
A sustained service interruption
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Overcurrents
Amperages in a conductor that are larger than those for which it is rated.
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Overcurrents can be caused by
Lightening, faults, improper design
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Fault
Bypass of an intended conduction path
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Fault current
Amperage of the resulting abnormal electrical flow
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Short circuit
Current that is bypassing a designed conducting path
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Short circuits can occur between (3)
- Between a phase and another phase
- Between a phase and the system neutral
- Between a phase and the ground
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Faults cause
Overcurrents
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Direct fault
2 phase wires contact one another. Ex: tree branch across 2 phase wires.
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Fault that affects the dielectric properties of a system for an instant, and no longer exists after the power has been restored.
Transient fault
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Repeated momentary interruptions in the same place due to the same cause often due to sporadic equipment malfunction
Intermittent fault
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Current surges
I rushes of electricity caused when electric devices like motors or transformers, are first turned on, they can draw several times their normal operating electrical load.
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Current surges can often occur when
Circuits are first re-energized following an outage
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Inductance
Electrification of a wire by passing it through a moving electromagnetic field.
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DC AND AC; Most transmissions line are ____ but some of the highest voltage transmission lines are ____ which can be less expensive and have less electrical loss over long distances.
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The value such as MWW, Mvar, amperes, frequency, or volts; derived from, or a subset of the System Operation Limits, which if exceeded could expose a widespread area of the Bulk Electric System to instability, uncontrolled separations, or cascading outages
IROL ; interconnection reliability operation limit
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These enable utilities to route power through various circuits as needed. They can compensate for portions of a system that are experiencing power failures. They protect circuits through dissconnect switches, circuit breakers, relays, and communication systems
Switchyards
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Transmission lines terminate at substations and ______
Switchyards
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Subtransmission lines energized between ___. And _____
23kv and 115kv
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A distribution 13.2 kV circuit is limited to about _______ miles
30 miles
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4kv is limited to about. ____ miles
10 miles
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Distribution substations reduce subtransmission voltage to usually between _____
2.4kv and 23kv
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Secondary voltage is
120 to 240 volts
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Secondary voltage has enough force to drive electricity about ____ ft
500ft
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Simplest distribution design with only one path of power flow. A single track of 3 phase lines from substation with taps running off them. Inexpensive, but no back up power customers during outage.
Radial systems
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Loop radial system
Joins 2 radial circuits together with a normally open switch at their junction. The switch can be closed so that parts of one circuit undergoing a power outage may be energized from the other.
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Loop primary circuit
Similar to loop radial system, that it begins a one substation, makes a loop and returns to the same sub station. It maintains power automatically when there is a fault in the line. Circuit breakers in the substation and auto re-closures along the line work in conjunction to isolate a fault.
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Convert mechanical energy to electrical energy using induction
Power generators
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Consist of large industrial magnets encased in wire windings that are known as field windings or field circuits
Gernerator
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Stationary part of a generator that contains field windings
Stator
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The changing intensity and direction of alternating current is graphed in a _______
Sign way
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Electric current that reverses its direction many times per second at regular intervals, typically used in power supplies
AC alternating current
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Alternating current is created by the ___
Change in direction of the oscillating magnetic poles.
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The time it takes for a magnet to complete a revolution
Cycle
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The number of cycles per second is measured in ___
Hertz or Hz
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Smooth grid functioning requires electrical generation to be syncronized at the same frequency. In North America, electricity in generated at a constant speed of _____
60 Hz, or 60 cycles a second
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A ____ is produced on a single winding
Phase
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Why is electricity generated in 3 phases?
Because stators (field winding encasement) are wound with three separate coils that are insulated from one another.
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The three separate coils in stators are set at ______Degrees apart to produce 3 phase voltage. 1/3 of a cycle
120 degrees
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Why the 3 phase coil arrangement at 120 degrees
Ensures against a break in electrical generation because there is no moment where all three phases are simultaneously at zero.
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Energized conductors are also called phases because____
Stator windings are connected to the electrical system in a closed circuit and each phase has it own line
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The majority of electricity in the world is produced by _____
Fuel heated steam turbine plants
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Steam turbine generators are high speed units that usually operate at ______ revolutions per minute to deliver _____Hz of output frequency
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Fuel heated steam turbine plants advantage and disadvantage
Reliable and provide a base load of electricity at a constant frequency, which is easily synchronized with other steam turbines in the electrical grid.
-contribute to climate change
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Power plants that don’t contribute to climate change, so they are increasingly advocated as desirable sources of electrical generation
Nuclear power plants
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This type of turbine generation is accomplished by routing hot exhaust gases from burning natural gas or oil directly to high-pressure combustion chambers where the gasses expand and spin turbines
Gas or combustion turbine
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Renewable energy sources are primarily inexhaustible. They include these 5 ex.
Wind, solar, geothermal. Ocean current
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Most common source of renewable generation
Hydroelectric
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2/3 of electric generation in Canada and 3/4 in Brazil is
Hydroelectric
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Hydroelectric facilities can be as large as ____ megawatts create no _____ or ______
- 700
- Green house gases or air pollution
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Low speed turbines usually operated in North America between 120 and 900 rounds per minute to provide 60 Hz through reduction gears
Hydroelectric turbines
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Disadvantages of hydro power - 3
- It’s capacity may be limited in drought years
- It can affect migrating fish
- Resulting backwater often floods large areas
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Second most significant source of renewable energy behind hydropower
Wind
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The largest wind turbines have a maximum capcity of _____ megawatts
6
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Challenges of wind energy 4
- Tend to be located for from load centers and constrained by access to the transmission system
- Wind speed can be intermittent, which can make output undependable
- Optimal wind speeds may not coincide with periods of peek demand
- Bird and bat mortality
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The most powerful solar power plants generate over ____ megawatts
500
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Technology that has been developed to expand geothermal power production to exothermal areas where temperatures are otherwise too low to exploit. Involves loading hot water or steam in a low pressure container.
Flash steam
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Disadvantages in wave/tidal power generation 4
- Appearance and noise
- Potential reduction in wave height from wave energy conversion
- Alteration of marine habitat
- Potential toxic releases
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Point absorbers, oscillating water columns, overtopping terminators, and attenuators are strategies for ______
Converting ocean wave to electrical energy
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Two types of tidal turbines
- Vertical axis
- Horizontal axis
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Vertical axis turbine vs horizontal
- Vertical have an upright shaft with a magnitized base encased in a stator on ocean floor. They have hydrodynamic wings that are spun by tidal action to drive the magnet
- Horizontal function like wind turbines but they are turned by tidal currents rather than wind
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Energized conductors are usually made of _____ or ______
Copper or aluminum
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Years ago, conductors were predominantly made of ____
Copper
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For conductors, this material has gained favor due to its relative light weight and low cost in spite of having only 60 to 80 percent of the conductivity of copper
Aluminum
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Advantages of aluminum for conductors 2
- Light weight means fewer structures and longer spans
- Provides opportunity to use larger gauge wire, which provides less resistance and allow higher voltage than thinner conductors
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Aluminum major disadvantage
Tends to stretch when it is heated during high electrical loads and elevated ambient temperatures
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ACSR - aluminum conductor steel reinforced
To minimize stretching and add strength, aluminum wire is stranded around a steel core
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Some distribution conductors are covered with weatherproofing but most transmission and distribution are ___
Bare
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Coated overhead primary aka tree wire. It’s not insulated and not safer than bare wire
Sometimes used in distribution wires in forests to provide some protection against faults from branches
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Neutral wires 2
Connect an electrical circuit or equipment to the earth or to some conducting body that serves in place of the earth. They also function as a safety device that ensure there is no difference in potential and no shock hazard among non-current carrying parts anywhere in the system
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Under normal circumstance ,do not carry a charge, but can carry primary voltages when there is a ground fault.
Neutral wire
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Work by providing a low resistance fault return path to the power source, and help facilitate proper overcurrents device operation during a ground fault.
Neutral wire
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Ground wires
Connect system neutral to earth
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Most multiphase distribution lines are built using ______ construction
Wye
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Wye construction consists of
3 phases and a grounded or neutral wire.
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In a Wye construction the potential difference between any two phases is about _____ times higher than the voltage difference between a phase and the neutral wire
1.73 times
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Neutral wire on top of pole double as lightning protection and is sometimes called
Static or shield wire
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Delta construction consists of
3 phases, but no neutral, so there is no fixed difference between phase to phase and phase to ground voltages
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Why should workers be alert to possibility of delta construction
They may mistake a phase for a neutral
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Unground cable consist of _______ in an insulated covering
All energized phases and neutral
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Primary lines have been install underground since
1880’s
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Primary cable often buried at ___ft and secondaries at ____ft
3, 2
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Used to shift load or reroute electricity between circuits during outages
Switches
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In an electric transmission or distubution system, the activation of a protective device
Operation
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Manually operated switch in distribution lines used to disconnect heavy electrical loads, capable of extinguishing an electric arc created by interrupting a heavy load.
Oil switch
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Manually operated switch, usually deployed where two circuits meet. Often used to reroute electricity to a circuit or circuit portion from an energized feeder. They are not designed to automatically interrupt electric load or be used as line protection form overload, short circuit, or fault
Air brake switch
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Transmission circuit breakers disconnect abnormalities from the system. They operate in response to three kinds of common irregularities____________
- Abnormally high amperage
- Abnormally low voltage
- Unequal current in 3 phases
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What is a relay and what does it do?
In transmission protection, they are low voltage switches. In response to voltage either stopping or starting to pass through them they will send signals to circuit breaker control mechanisms .
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Relay detect measurable ____ and and cause circuit breakers to ______
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Most common zones for circuit breaker on transmission system 3
- Generator
- Transformer
- Bus
- Lines
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The closer a fault to a substation the ____
The more customers likely without service
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The principle protective devices in distribution substations just as they are in transmission sub stations
Circuit breaker
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An open circuit breaker _____the entire distribution circuit
De-energizes
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A switch that automatically interrupts the flow of electricity if a circuit becomes overloaded or another dangerous problem occurs
Circuit breaker
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Designed to reset quickly to give the cause of a fault an opportunity to clear that may be caused by brief instance; tree or animal contact, conductor clash
Automatic line reclosure
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A permanent operation is called a
Lockout
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In distribution lines, automatic reclosures are installed in ______
Substations
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Lockouts require lineman to
Manually reset the device
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Automatic reclosures often have current ratings between ___ and ___ amps
10, 600
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Transient fault in an electrical system lasting from 33 to 133 milliseconds
Momentary interruption
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Electric customers becoming intolerant to _____ because they can disrupt clocks, computers, electrical equipment
Transient outages/ momentaries
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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.
Line sectionalizer
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How does a line sectionalizer work
Cuts off current when an upstream reclosure operates, isolating a fault in the line beyond the sectionalizer
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The simplest type of short circuit protection are installed on distribution lines to segregate both equipment and line sections, including taps.
Fuses
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Fuses designed to operate above 600v
Cutouts
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The farther from substation the _____ the fuse
More sensitive
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Insulator made of poor conductive material such as 6
Porcelain, glass, ceramic, epoxy, polymer, fiberglass
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Transformers raise or lower voltage through
Inductance
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Faraday law of inductance
A wire coil can be electrified by passing by passing it through a moving electrical field, and the movement can be provided by AC
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Electrical flow in an unintended direction
Back feed
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On step up transformers the primary voltage is. _____ than the secandary voltage. On step down transformers the primary voltage is ____ than the secondary voltage
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Each of the two coils in a transformer has a different number of turns. The ration of one to the other is _____. While the proportion of primary to secondary voltage is the ____. These two are ______
- Turns ratio
- Voltage ratio
- Identical
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Wattage in primary line and secondary line have to be
Equal
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Functioning like adjustable transformers, these are capable of either increasing or decreasing the circuit voltage as needed due to voltage irregularities that can occur from an array of operational conditions such as changing load, voltage loss
Voltage regulator
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Temporarily hold and release voltage to boost voltage, eliminate sparks, smooth the flow of direct current and protect against momentary voltage. Like Short lived batteries, but batteries store electricity chemically, these in an electric field.
Capacitor
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The most common capacitor design consists of
Two parallel conductive plates separated by insulation
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The two prominent indices used to quantify reliability are
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SAIFI - stands for ____ and is a measure of ______. The formula is _______
- System Average Interruption Frequency Index.
- Measure of the number of outages experienced by the average customer over a year(or any specific time period”)
- Formula - Total number of customer interruptions / total number of customers
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