Posts Tagged ‘electricity’

BART uses electricity to run, but what sources are being transformed in to electricity?

Monday, February 18th, 2013

Question by Gemini: BART uses electricity to run, but what sources are being transformed in to electricity?
I know that BART uses electricity to run the trains. But what sources make the electricity being used by BART, fossil fuel, natural gas or what sources?
And how much you pay for the parking in the BART parking lots? Is it still cheaper than driving a car?
The BART in the Bay Area

Best answer:

Answer by anywherebuttexas
Despite the pie-in-the-sky dreaming of environmentalists, most marginal electrical demand is going to be supplied by fossil fuel plants. True everywhere in the US.

As for the efficiency of public transportation, that’s more religion than science. The only place I’ve seen an attempt to compare the fuel efficiency of public transportation vs alternatives is in this report, on the planned 2nd Avenue Subway in NYC:

http://www.mta.info/capconstr/sas/documents/sdeis/chapter13.pdf

If you read the report, you might be surprised to discover that the subway would consume more fuel than the traffic it replaces. But read the footnotes, the real numbers are much worse. The conversion factors used are 133,000 BTU per gallon of gasoline and 3,413 BTU’s per KWHR of electricity. This is an error, which makes the subway look much better than it really is. Here’s the problem. Gasoline is burned directly in an automobile, at an efficiency of under 25%. But while electricity is consumed at an efficiency of 80% for the electric subway motor, it takes a considerably greater amount of energy to create the power consumed. In order to deliver 1 KWHR to the power outlet, a source must be consuming more than 1 KWHR worth of fuel. I’ll explain:

Since there is next to no opportunity for wind or solar power in NYC, and no nuclear plant has been build there in 50 years, marginal demand must be met by fossil fuel plants. A steam turbine plant fueled by natural gas or oil is perhaps 35% efficient, but let’s be generous and say 50%. The distribution network…power lines and transformers…might operate at 95% efficiency. Finally, subways in NY run on DC power, so what comes off the line must be rectified, at perhaps 75% efficiency. If you start with enough natural gas to produce 1000KWHRS, you end up with 1000x.50x.95x.75 KWHRS, only 356 KWHRS is actually delivered to the electric motor. If the electric motor is 80% efficient, 284 KWHRS actually produces useful work. If 1000 KWHRS of gasoline is burned in a 25% efficient car, 250 KWHRS actually produce useful work.

While the motors end up being of comparable efficiency, the subway system turns has a much lower load factor than the car. That is, if two people ride in a car, it’s about half loaded. That’s the way it’s going to be on average. A subway car must roll up and down the track day and night, in order to provide a reasonably attractive alternative. But it’s only running at it’s full rated load factor for about four hours a day. The rest of the time, energy is expended pushing mostly empty cars up and down the track. All in all, it would be more fuel efficient to drive a Hummer than take a subway.

Know better? Leave your own answer in the comments!

Lec 1 | MIT 8.02 Electricity and Magnetism, Spring 2002

Wednesday, September 19th, 2012

What holds our world together? | Electric Charges (Historical) | Polarization | Electric Force | Coulomb’s Law View the complete course at: ocw.mit.edu Spanish translation courtesy of Universidad CAECE Mar del Plata. Romanian translation courtesy of Mihai Olteanu. License: Creative Commons BY-NC-SA More information at ocw.mit.edu More courses at ocw.mit.edu
Video Rating: 4 / 5

Lec 28 | MIT 8.02 Electricity and Magnetism, Spring 2002

Tuesday, August 21st, 2012

Index of Refraction Poynting Vector Oscillating Charges Radiation Pressure Comet Tails Polarization (Linear, Elliptical, and Circular) View the complete course at: ocw.mit.edu License: Creative Commons BY-NC-SA More information at ocw.mit.edu More courses at ocw.mit.edu

does electricity pass through the tracks on a electric train?

Thursday, June 14th, 2012

Question by Knights Templar: does electricity pass through the tracks on a electric train?
what creates the circuit with overhead wiring on electric trains and if it passes through the tracks why whats stops electrocution of people walking on tracks

Best answer:

Answer by Bob B
The high voltage to drive the train is carried on the conductors hung above the trackway. Since the tracks only provide a path to carry the current to ground, they aren’t at an elevated voltage level.

Know better? Leave your own answer in the comments!

Lec 19 | MIT 8.02 Electricity and Magnetism, Spring 2002

Sunday, April 29th, 2012

Vacation Special How do Magicians levitate women? (with demo) Electric Shock Treatment (no demo) Electrocardiogram (with demo) Pacemakers Superconductivity (with demo) Levitating Bullet Trains Aurora Borealis View the complete course at: ocw.mit.edu License: Creative Commons BY-NC-SA More information at ocw.mit.edu More courses at ocw.mit.edu
Video Rating: 4 / 5

what type of electricity used in electric trains? DC or AC ? What is the voltage?

Sunday, June 19th, 2011

Question by koolgirisho: what type of electricity used in electric trains? DC or AC ? What is the voltage?
Electric trains

Best answer:

Answer by TJ
DC
duh!
ac is air conditioning!
lmao
jk
idk
and idc

Know better? Leave your own answer in the comments!

Where do electric trains get the electricity to power their engines?

Saturday, March 26th, 2011

Question by Jay Gee: Where do electric trains get the electricity to power their engines?
How does the energy in a fuel determine an engines performance in torque and power? Are trucks etc, that need a lot of power stuck with oil as a fuel because of it’s btu per gallon ?

Best answer:

Answer by jim m
From coal burning electric power or hydropower.

What do you think? Answer below!

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