Ac vs. DC background
 

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AC vs. DC

History of AC and DC power generation

 

Alternating Current (AC)

1.      Who – Nikola Tesla (1856-1943) was an inventor and a mechanical and electrical engineer. He was one of the most important contributors to the birth of commercial electricity, and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries. Most importantly his works formed the basis of modern alternating current electrical power systems which includes the polyphase system of electrical distribution and the AC motor.

 

2.      He promoted alternating current for electrical power distributions along with George Westinghouse.

 

Direct Current (DC)

1.      Thomas Edison (1847-1931) was an American inventor, scientist and businessman who developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. Most importantly he originated the concept and implementation of electric-power generation and distribution to homes, businesses, and factories – a crucial development in the modern industrialized world.

 

2.      He promoted direct current for electrical power distributions.

 

 

DC was easier for any ordinary citizen to understand, of course -- it required no calculus, nor the sort of `mental vision' of voltage and current flows creating rotating magnetic fields that would spin a motor -- but AC clearly held the technical edge for centralized power generation and long-distance transmission. In addition, AC could carry more energy. Tesla and Westinghouse won the war.

 

Theory of AC and DC power

Characteristics and Advantages of AC:  Alternating Current oscillates forward and backward at a specific frequency, 60 Hz in the US and 50 Hz in many other parts of the world.  Higher frequencies can be used with lighter electrical machines.  For example, aircraft typically use 400 Hz.

One advantage of AC is that the voltage can easily be changed by use of a transformer.  At a high voltage, not much heat is lost in transmission, but high voltages are potentially dangerous.  Therefore AC is transmitted over long distances at a high voltage then is transformed to a lower voltage before going into homes.

Characteristics and Advantages of DC:  DC power maintains a constant direction of current.  One advantage of DC power is there is no reactance in the line.  This allows higher power transfer capability, higher capacity utilization of generators, and less of a voltage drop along the line.  DC also has a lower line resistance than AC because of the “skin effect” in AC.  This is when charge is carried mostly near the outside of the wire.

In the DC system, power is just the real component.  This means that the transmission system operator need not worry about the sufficiency of reactive power to maintain the security and stability of the system.

In DC, there is no frequency, so generators connected to the transmission grid do not need to be synchronized.

The DC system does not introduce susceptance along the line thus removing the effect of changing current and over voltages in the system.

Analysis of DC systems only involves real numbers, while AC systems involve complex numbers.

Generation and Transportation

AC Power

AC power generation – AC power is generated in large power plants. Conventional generators produce AC naturally.

AC power generating stations- There are multiple types of AC power generating stations among them:

·         Coal Power

·         Oil Power

·         Natural gas power

·         Nuclear power

·         Hydro electric

All these different methods basically do one thing. They use water or steam to turn a turbine that spins a generator.

Transmission-Power from generating plants typically leaves the plant at high voltage and is carried over high voltage transmission lines for up to 300 miles. The power then reaches a substation where it is converted by means of transformers to a lower voltage for local lines and then converts to an even lower voltage at a transformer near the intended destination.

High Voltage lines- Long distance power distribution lines carrying 155,000 to 765,000 volts. Can extend up to 300 miles from power plant.  End at substation

Substation-Use large transformers to step down power into 10,000 volts

Transformers- Use induction coil to downgrade power.

transformer.bmp

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DC Power

DC power generation- DC power is generated primarily by solar cells and batteries

Batteries- Use electrochemical reaction to produce power. Electrons are forced to move from low potential to a higher state of potential. This typically involves 2 different metals on unequal electron affinity and an acid to liberate these electrons. This creates direct electric current.

Types:

  • Zinc-carbon battery - Also known as a standard carbon battery, zinc-carbon chemistry is used in all inexpensive AA, C and D dry-cell batteries. The electrodes are zinc and carbon, with an acidic paste between them that serves as the electrolyte.
  • Alkaline battery - Alkaline chemistry is used in common Duracell and Energizer batteries, the electrodes are zinc and manganese-oxide, with an alkaline electrolyte.
  • Lead-acid battery - Lead-acid chemistry is used in automobiles, the electrodes are made of lead and lead-oxide with a strong acidic electrolyte (rechargeable).
  • Nickel-cadmium battery - The electrodes are nickel-hydroxide and cadmium, with potassium-hydroxide as the electrolyte (rechargeable).
  • Nickel-metal hydride battery - This battery is rapidly replacing nickel-cadmium because it does not suffer from the memory effect that nickel-cadmiums do (rechargeable).
  • Lithium-ion battery - With a very good power-to-weight ratio, this is often found in high-end laptop computers and cell phones (rechargeable).

History of AC and DC power generation

 

Alternating Current (AC)

1.      Who – Nikola Tesla (1856-1943) was an inventor and a mechanical and electrical engineer. He was one of the most important contributors to the birth of commercial electricity, and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries. Most importantly his works formed the basis of modern alternating current electrical power systems which includes the polyphase system of electrical distribution and the AC motor.

 

2.      He promoted alternating current for electrical power distributions along with George Westinghouse.

 

Direct Current (DC)

1.      Thomas Edison (1847-1931) was an American inventor, scientist and businessman who developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. Most importantly he originated the concept and implementation of electric-power generation and distribution to homes, businesses, and factories – a crucial development in the modern industrialized world.

 

2.      He promoted direct current for electrical power distributions.

 

 

DC was easier for any ordinary citizen to understand, of course -- it required no calculus, nor the sort of `mental vision' of voltage and current flows creating rotating magnetic fields that would spin a motor -- but AC clearly held the technical edge for centralized power generation and long-distance transmission. In addition, AC could carry more energy. Tesla and Westinghouse won the war.

 

 

Sources

http://www.bookrags.com/research/alternating-current-woi/

http://science.howstuffworks.com/electricity5.htm

http://www.jcmiras.net/jcm/item/86/

www.howstuffworks.com