8) Why is DC better than AC in long-distance transmission?
DC is more economical than AC for long distance transmission. A DC line requires fewer conductors than an AC line, i.e. two wires versus three for an AC line. In addition, it requires less insulation than AC lines. These considerations mean that DC transmission towers take up less space, meaning less land is used for right-of-way. With present day prices, transmission over 200 miles is more economical with DC than AC.
DC lines have less losses. DC does not suffer from the skin effect, which is a characteristic of AC that causes the effective resistance of the conductor to increase. Reactive losses associated with AC also do not exist in DC.
DC has no synchronization issues. DC enables power transmission between unsynchronized AC transmission systems. This characteristic of DC reduces the likelihood of cascading blackouts and thus stabilizes a network against disturbances due to rapid changes in power.