Final answer:
AC and DC voltage types on transmission lines may require a corona shield due to the high-voltage conditions that can lead to corona discharge. The usage of high voltage is prevalent in AC transmission lines to minimize resistive losses, which makes AC susceptible to corona effects. DC transmission can also experience corona discharge, albeit less frequently than AC.
Step-by-step explanation:
The question is asking which voltage types on transmission lines require a corona shield. The usage of corona shields is generally associated with electric power transmission lines where high voltage is used to transmit power over long distances, and this typically involves alternating current (AC) and direct current (DC). In AC transmission, the high voltage is necessary to minimize resistive heating losses, and due to the nature of AC voltage, corona discharge can be a significant issue. This is why AC transmission lines may require corona shields. DC transmission can also exhibit corona discharge under certain high-voltage conditions, although it's less common than with AC.
Additionally, radio frequency (RF) can be generated as a byproduct of high-voltage AC transmission lines due to the oscillating currents producing electromagnetic waves. However, RF itself in the context of transmission lines isn't typically associated with corona discharge, rather it's a form of energy loss. Therefore, the answer to the question would be option a. AC, DC as both of these voltage types in power transmission may require corona shields to mitigate the effects of corona discharge.