DC generation back during Edison

[cmos]

DC generation back during Edison...

Hi all,

As most EE's know, back in the late 1800's, there was a debate on how electricity should be generated and distributed. Edison was the advocate of distributing DC electricity (since he owned all the appropriate patents) while Westinghouse and Tesla advocated the use of AC electricity. Clearly history was kind to Westinghouse and Tesla in this regard.

I am wondering though, how did Edison generate his form of electricity? I simply cannot imagine "huge vats" of galvanic cells distributing electricity to a nearby town.

Regards!

 

[mgb_phys]

DC generators aren't very different from AC generators - at least in the technology needed to build and operate them.

 

[turbo]

DC power distribution is not practical over long distances. Tesla knew this and convinced George Westinghouse of the practicality of AC. This is pretty thoroughly covered in popular accounts of the AC-DC battle.

 

[zeitghost]

Instead of using an alternator driven by a steam engine to give AC, he used a dynamo driven by a steam engine to give DC.

The problem with DC is that you can't use transformers to increase or decrease the voltage, which is what makes grid power transmission so much more efficient by reducing the I*2R power loss in the conductors.

 

[mgb_phys]

DC power distribution is not practical over long distances.

Long distance DC does have some advantages. Especially if you are tying different power grids together or you have underground or underwater cables.
But you need modern solid state gear to efficently convert DC voltages.

 

[turbo]

Long distance DC does have some advantages. Especially if you are tying different power grids together or you have underground or underwater cables.
But you need modern solid state gear to efficently convert DC voltages.

My point was that if electrical distribution systems were going to be built to provide distant homes and businesses with power, AC was the only practical way. The transmission lines could be much longer and much smaller with less loss if you stayed with AC. Yes, you needed step-up and step-down transformers to make long-distance transmission practical, but Tesla knew that it could be done, and Westinghouse had faith in him. I figured that everyone knew the history of the AC-DC battle and the practicalities that determined the winner.

 

[mgb_phys]

I know - I was just adding one of those thread hijacking off-at-a-tangent exceptions for which PF is famous!

I figured that everyone knew the history of the AC-DC battle and the practicalities that determined the winner.

The politics and dirty tricks that determiend the winner are also interesting.

 

[triden]

If there were a practical way to "transform" DC voltages up and down, wouldn't it be more practical for transmission purposes? It was my understanding that HV AC power emits a lot of EMF radiation which has interference issues and line loss. Also, wouldn't it make sense to feed houses AC instead of DC? This would mean almost all electronic equipment wouldn't need bulky power supplies.

 

[zeitghost]

There is a way to transform DC up & down...

It's called a static inverter.

The power line under the English Channel that connects the UK power system to France uses DC to avoid having to synchronise the generators on either side of the link.

This possibility didn't exist before the advent of high power semiconductors.

 

[triden]

My point was that if electrical distribution systems were going to be built to provide distant homes and businesses with power, AC was the only practical way. The transmission lines could be much longer and much smaller with less loss if you stayed with AC. Yes, you needed step-up and step-down transformers to make long-distance transmission practical, but Tesla knew that it could be done, and Westinghouse had faith in him. I figured that everyone knew the history of the AC-DC battle and the practicalities that determined the winner.

According to a wikipedia article http://en.wikipedia.org/wiki/High-voltage_direct_current , HVDC lines can be much longer and much smaller than AC lines with less loss. What is the reasoning behind your idea?

quote from wikipedia:

The advantage of HVDC is the ability to transmit large amounts of power over long distances with lower capital costs and with lower losses than AC. Depending on voltage level and construction details, losses are quoted as about 3% per 1000 km. High-voltage direct current transmission allows efficient use of energy sources remote from load centers.

Long undersea cables have a high capacitance. While this has minimal effect for DC transmission, the current required to charge and discharge the capacitance of the cable causes additional I2R power losses when the cable is carrying AC. In addition, AC power is lost to dielectric losses.

HVDC can carry more power per conductor, because for a given power rating the constant voltage in a DC line is lower than the peak voltage in an AC line.

 

[turbo]

According to a wikipedia article http://en.wikipedia.org/wiki/High-voltage_direct_current , HVDC lines can be much longer and much smaller than AC lines with less loss. What is the reasoning behind your idea?

quote from wikipedia:

Your example is application-specific. Read the material you linked to.

Then consider how Edison could have managed to transform HVDC to usable (safe) voltages at the user end. Not possible at the time - the technology did not exist. For the time, the available, technology, and the application (efficient, long-distance transmission of power) AC was clearly superior to DC.

 

[Pumblechook]

DC generators are like DC motors. They have commutators which 'mechanically' convert the induced AC into DC. These days in cars.. simpler and more reliable alternators are used and simiconductor rectifiers convert the AC to DC.

DC genertors don't produce a smooth output like a battery but DC with a lot of AC ripple.


http://www.koehler.me.uk/animation/e_and_m_dc_gen_1.htm