Transcript Wimshurst Machine

Wimshurst Machine
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two large contra-rotating discs mounted in a
vertical plane, two cross bars with metallic
brushes, and a spark gap formed by two
metal spheres.
two insulated disks and their metal sectors
rotate in opposite directions passing the
crossed metal neutralizer bars and their
brushes.
imbalance of charges is induced, amplified,
and collected by two pairs of metal combs
with points placed near the surfaces of each
disk.
The positive feedback increases the
accumulating charges exponentially until a
spark jumps across the gap.
The accumulated spark energy can be
increased by adding a pair of Leyden jars, an
early type of capacitor suitable for high
voltages
Van de graf generator
• an electrostatic
machine which uses a
moving belt to
accumulate very high
electrostatically stable
voltages on a hollow
metal globe.
Van de graaff generator
• Video:
http://www.youtube.com/watch?v=sy05B32X
TYY
Faraday’s Disk
• A copper disc rotating between
the poles of a horseshoe magnet.
produced a small DC voltage,
and large amounts of current.
• First electromagnetic generator
Dynamos
• First generator able to produce electricity for
industrial purposes
• First dynamo was built by Hippolyte Pixii in 1832.
• a stationary structure, which provides a constant
magnetic field, and a set of rotating windings
which turn within that field.
• Magnetic field may be provided by one or more
permanent magnets or by one or more
electromagnets, which are usually called field
coils.
Pixii's dynamo
Dynamos
• Produce a direct current
• Basis for later devices such as the electric
motor, the alternating-current alternator, and
the rotary converter.
• Developed as a replacement for batteries
Modern electrical power plants
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Boiler Unit: Almost all of power
plants operate by heating water in a
boiler unit into super heated steam
at very high pressures. The source of
heat from combustion reactions may
vary in fossil fuel plants from the
source of fuels such as coal, oil, or
natural gas. Biomass, waste plant
parts, solid waste incinerators are
also used as a source of heat. All of
these sources of fuels result in
varying amounts of air pollution, as
well as carbon
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In a nuclear power plant, the fission
chain reaction of splitting nuclei
provides the source of heat.
Modern electrical power plants
• The super heated steam
is used to spin the
blades of a turbine,
which turns a coil of
wires within a circular
arrangements of
magnets.
Modern Electric power plants
• Cooling Water: After the
steam travels through the
turbine, it must be cooled
and condensed back into
liquid water to start the
cycle over again. Cooling
water can be obtained from
a nearby river or lake. An
alternate method is to use a
very tall cooling tower,
where the evaporation of
water falling through the
tower provides the cooling
effect.
Getting the electricity from the plant to the
light switch
Power transmission
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Power plants are not located near population centers
Need to get the power from the plant to the users
Edison created the first power system in New York City in 1882.
Used direct current. Could only deliver electricity to customers
closer than 1.5 miles away from the power station.
• Westinghouse proposed using AC current, which could be more
easily and cheaply transmitted. Resulted in the “War of Currents”
– Edison waged a PR campaign, claiming AC current was far more
dangerous as at frequencies near 60HZ, it had a greater potential to
cause cardiac fibrillations.
– He and his workers publically electrocuted animals to make their
point.
• Edison opposed capital punishment, but in an effort to make his
point about AC current, he secretly funded the development of the
first electric chair.
Power transmission
• Energy is lost in transmission lines
• Materials that allow electrons to flow through
them (current) are called conductors.
• Every conductor has some resistance to the
flow of current.
• Energy is lost as the current flows through the
transmission lines
• Relationship between voltage, current and the
resistance to current flow is given by V = IR
Power transmission
• The losses in the line are proportional to the resistance
and the current squared or RI2 and the power in the
line is proportional to VI (voltage times current)
• The solution to these losses is to transmit the power at
much higher voltages than the users need, and step
the voltage down along the way. That way the current
in the line is low, so the power losses are low.
• So the voltage is increased before the electricity leaves
the power station and then decreased as needed.
• This is accomplished with a device called a transformer
Transformers
• No not these guys…..
Transformers
• A device that transfers energy from one
electrical circuit to another using the concept
of induction
• A changing current in the first circuit (the
primary) creates a changing magnetic field.
This changing magnetic field induces a
changing voltage in the second circuit (the
secondary). This effect is called mutual
induction.
Transformers
• The number of coils in the
windings determine if the
voltage is increased
(stepped up) or
decreased (stepped
down)
• If the number of coils in
the secondary is larger
than the primary, voltage
is stepped up, if it is less it
is stepped down.
Power transmission
• At the power station, the generator produces
13-25kV.
• A step up transformer boosts this to 115 to
765 kV.
• Substations reduce the voltages for local
distribution.
• Transformers on power poles reduce it further
to the 240 V generally fed into our homes.
Power Transmission
Health Risks from Power Lines
• Power lines are live, if you touch them (and
are in contact with the ground) you provide
the current a path to ground. AC currents can
induce heart fibrillations and cause death.
• NO strong link to overhead power lines and
increased cancer due to the lines themselves.
Power Grid
• A network of power transmission systems
• Usually more than one path between points
on a network
Power Grid
• The US and Canadian power companies are integrated
into a single power grid
• Allows backups in case of emergencies, utilities can
trade electrical energy and it is economical
• Circuit breakers (devices which cut off the flow of
electricity through the circuit) protect against sudden
surges in power
• They can isolate the problem and help the grid reroute
the power flow
• If the problem is not isolated, the problem can spread
throughout major portions of the grid, causing power
interruptions we call blackouts.
US Power Grid
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Three grids cover the contiguous 48 states and
parts of Canada and Mexico and are known as the
Western Interconnection, the Eastern
Interconnection, and the Electric Reliability Council
of Texas (ERCOT) Interconnection. Collectively they
make up what is called the national power grid
Each grid may be broken up into smaller power
sharing arrangements, described below.
ECAR - East Central Area Reliability Coordination
Agreement
ERCOT - Electric Reliability Council of Texas
FRCC - Florida Reliability Coordinating Council
MAAC - Mid-Atlantic Area Council
MAIN - Mid-America Interconnected Network
MAPP - Mid-Continent Area Power Pool
NPCC - Northeast Power Coordinating Council
SERC - Southeastern Electric Reliability Council
SPP - Southwest Power Pool
WSCC - Western Systems Coordinating Council
Power interruptions
• Dropouts -momentary (milliseconds to seconds) loss of
power typically caused by a temporary fault on a power
line.
• Brownouts -a drop in voltage in an electrical power supply,
so named because it typically causes lights to dim. Can
occur if the demand for electricity on the grid is greater
than what it can produce
• Blackouts - total loss of power to an area
• Note that it doesn’t take a bad storm to cause problems
with power line. If demand increases and the power on the
line increases, the lines heat up and stretch, causing them
to sag. If they come in contact with a tree, then the line can
short out.
2003 Blackout
• Affected much of the Northeastern US and parts of Canada August 14,
2003.
• Timeline: (Thank you Wilkipedia)
• # 12:15 p.m. Incorrect telemetry data renders inoperative the state
estimator, a power flow monitoring tool operated by the Ohio-based
Midwest Independent Transmission System Operator (MISO). An operator
corrects the telemetry problem but forgets to restart the monitoring tool.
• # 1:31 p.m. The Eastlake, Ohio generating plant shuts down. The plant is
owned by FirstEnergy, an Akron, Ohio-based company that had
experienced extensive recent maintenance problems.
• # 2:02 p.m. The first of several 345 kV overhead transmission lines in
northeast Ohio fails due to contact with a tree in Walton Hills, Ohio.
• # 2:14 p.m. An alarm system fails at FirstEnergy's control room and is not
repaired.
• # 2:27 p.m. A second 345 kV line fails due to contact with a tree.
Timeline
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# 3:05 p.m. A 345 kV transmission line known as the Chamberlain-Harding line fails in Parma, south of Cleveland,
due to a tree.
# 3:17 p.m. Voltage dips temporarily on the Ohio portion of the grid. Controllers take no action.
# 3:32 p.m. Power shifted by the first failure onto another 345 kV power line, the Hanna-Juniper interconnection,
causes it to sag into a tree, bringing it offline as well. While MISO and FirstEnergy controllers concentrate on
understanding the failures, they fail to inform system controllers in nearby states.
# 3:39 p.m. A FirstEnergy 138 kV line fails.
# 3:41 p.m. A circuit breaker connecting FirstEnergy's grid with that of American Electric Power is tripped as a 345
kV power line (Star-South Canton interconnection) and fifteen 138 kV lines fail in rapid succession in northern
Ohio. Later analysis suggests that this could have been the last possible chance to save the grid if controllers had
cut off power to Cleveland at this time.
# 3:46 p.m. A sixth 345 kV line, the Tidd-Canton Central line, trips offline.
# 4:06 p.m. A sustained power surge on some Ohio lines begins an uncontrollable cascade after another 345 kV
line (Sammis-Star interconnection) fails.
# 4:09:02 p.m. Voltage sags deeply as Ohio draws 2 GW of power from Michigan, creating simultaneous
undervoltage and overcurrent conditions as power attempts to flow in such a way as to rebalance the system's
voltage.
# 4:10:34 p.m. Many transmission lines trip out, first in Michigan and then in Ohio, blocking the eastward flow of
power around the south shore of Lake Erie. Suddenly bereft of demand, generating stations go offline, creating a
huge power deficit. In seconds, power surges in from the east, overloading east-coast power plants whose
generators go offline as a protective measure, and the blackout is on.
# 4:10:37 p.m. The eastern and western Michigan power grids disconnect from each other. Two 345 kV lines in
Michigan trip. A line that runs from Grand Ledge to Ann Arbor known as the Oneida-Majestic interconnection
trips. A short time later, a line running from Bay City south to Flint in Consumers Energy's system known as the
Hampton-Thetford line also trips.
Timeline
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# 4:10:38 p.m. Cleveland separates from the Pennsylvania grid.
# 4:10:39 p.m. 3.7 GW power flows from the east along the north shore of Lake Erie, through
Ontario to southern Michigan and northern Ohio, a flow more than ten times greater than the
condition 30 seconds earlier, causing a voltage drop across the system.
# 4:10:40 p.m. Flow flips to 2 GW eastward from Michigan through Ontario (a net reversal of 5.7
GW of power), then reverses back westward again within a half second.
# 4:10:43 p.m. International connections between the United States and Canada begin failing.
# 4:10:45 p.m. Northwestern Ontario separates from the east when the Wawa-Marathon 230 kV
line north of Lake Superior disconnects. The first Ontario power plants go offline in response to the
unstable voltage and current demand on the system.
# 4:10:46 p.m. New York separates from the New England grid.
# 4:10:50 p.m. Ontario separates from the western New York grid.
# 4:11:57 p.m. The Keith-Waterman, Bunce Creek-Scott 230 kV lines and the St. Clair-Lambton #1
and #2 345 kV lines between Michigan and Ontario fail.
# 4:12:03 p.m. Windsor, Ontario and surrounding areas drop off the grid.
# 4:13 p.m. End of cascading failure. 256 power plants are off-line, 85% of which went offline after
the grid separations occurred, most due to the action of automatic protective controls.
2003 Northeastern Blackout
• 50 million people in the
dark
• Cost economy 1 billion
dollars