Central Electricity Generating Board
The Central Electricity Generating Board was the name given to the nationalised Electric supply industry during the period 1957 - 1990 and therefore is relevant to the railway in connection with the Llyn Ystradau power scheme, the Deviation, and other matters.
Effectively, from 1990, the electricity supply industry has been splitup and privatised. The CEGB didnt actually cease to exist until 2001. See Wikipedia for further information.