Why transmission is always done in a.c but not in d.c?

Question

Why transmission is always done in a.c but not in d.c?

Answer 1

Not alway...

Alternative current allows the use of transformers to step the voltage up and back down at the other end.

Power = voltage x current.

The more current, the larger the required conductors.  Raising the voltage allows the use of smaller conductors for the same amount of power.

The lower current also results in reduced line losses.  The losses in the conductor are proportionate to the square of the current.  i²R

That being said, there are direct current transmission lines in the world.  The first ones were installed in the early 1950's.  They offer several advantages over a.c. transmission lines.  Read the link below for more details.

Answer 2

I assume you mean power transmission, as most automobile transmissions are in steel and aluminum.

AC allows you to use transformers, which can change the voltage to very high numbers, which reduces the current to a low value. Since line losses are due to current, this allows you to ship large amounts of power for long distances without significant losses.

DC, you can't easily change voltages, so you have to transmit the low voltage of 120 volts, and that you can only do for a few hundred yards.

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Answer 3

thomas edison started to build electrical grids using d.c. in NY City but found that because of the resistance of the wire, he would have to build a power station about every couple of miles. electricity in a d.c. circuit has to travel all the way around through the curcuit from (-) to (+). that could be a LONG way, the wire sucks up all the power. . nicola tesla built an a.c. grid in upstate NY and got much better results because the electricity in an a.c. circuit acutally travels back and forth, a short distance, which over comes the wire resistance and delivers the power.

Answer 4

P = EI (Power = Voltage x Current).  For a given amount of required power you can have either low voltage and high current or high voltage and low current (for AC or DC power).  If you select high current you must provide very heavy conductors to carry it without melting (and copper, etc. is very expensive not to mention the cost of much stronger transmission towers).  Very high voltage and lower current is a good option with either AC or DC power.  AC power has the advantage of efficient conversion using transformers that step up voltage for transmission and step down voltage for the customer's equipment.  High current leads to heating effects that lose power due to I square R losses (current squared x resistance).  AC has an added advantage because the electrical pressure alternates (perhaps 60 cycles per second).  The steady electrical pressure of high  DC voltage tend to create conductive paths through insulators sometimes leading to component failures.  AC was also considered to be less dangerous to people (workers and customers) because a shock would cause muscles to flex and unflex whereas DC might cause a muscle to flex only holding on to the wire, etc.