subject: The Pros And Cons Of Transmission Dc [print this page] When electricity was discovered in the late nineteenth century it was first transmitted to people for domestic use via direct current. However inventions brought to the discovery of induction motors which made electricity cheaply available for those who lived nearby because it would be transmitted as alternating current. Transmission D. C. Was later to become popular in the mid and late twentieth century and it has continued to be.
The reason is because direct current transmission has long term advantages compared to alternating current. Direct current systems tend to have lower resistance compared to the competing alternating current systems. Overhead cables used in AC systems develop a skin effect along the way due to the frequency and incur more losses than a DC one would.
Underground cables usually develop some parasitic capacitance which causes a power loss when transmitting. An AC system requires that extra current be flowing in the line to charge the capacitor. Although direct current lines also have such losses and leakages, they are usually very minimal and can be neglected.
Transmission D. C. Ensures that only real power is transmitted and therefore the lines have high power transfer capability. Not a single reactance is noted along the line which ensures that no voltage drop is recorded along the way to stations. All generators are utilized to their full capacity therefore efficiency is almost 100 percent.
Research has shown that transmitting electricity by DC means protects the supply from electromagnetic pulses and other interruptions that may occur on the way. The frequency is zero and therefore does not require synchronization. Analysis of the same is much easier because real values are used with no complex numbers that usually complicate the analysis process.
The system is also a good one because it is cost effective in terms of the cables required to transmit. An AC system requires more cables than a direct current one. It is also possible to connect two asynchronous stations directly.
However, transmitting electricity this way is only practical for long distances where cables become expensive when used. This is because the inversion and rectification stages do require power electronics circuits that are usually very costly. It therefore becomes useful when the overall cost of cables for alternating current is so high that it exceeds the cost of the switching circuits. Metering direct current is also very hard and power flow becomes hard to monitor. Interrupting the current when large fault currents occur is also difficult.
