The power transfer capacity of an existing AC transmission line may be increased by conversion to
DC. The main difference between AC and DC is that stability constraints put an upper limit on the
power capacity of long AC lines, while DC lines are can be operated up to the thermal limit of the line.
Another reason is that the voltage withstand of the insulation is better utilized by the constant DC
voltage compared to the time-varying AC voltage. Corona effects at high voltage levels are also less
severe with DC compared with AC, which may allow a comparatively high DC voltage to be used.