Wimshurst Machine• 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=sy05B32XTYY

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• 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

• 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• 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• 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• # 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• # 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