hi
well i know what you wants to know, actualy the reason behind using different copper strands, well u have noticed that where ever the DC voltage is present u will see a solid conductor whose diameter depends on the amp the system needs , higher the amps need diameter will be greater, but in Ac power system we uses a wire consists of different copper strands as of losses and is better for long distance, there are some losses due to sine wave of AC , to minimize these losses we uses different strands instead of one . In DC the voltage is constant so dont need to have different strands.