The transmission of electrical energy, and particularly some of the problems, together with the facilities required for the development of apparatus for transmission substations are discussed. Transmission substations have not changed much in appearance over the years, although they have developed considerably in voltage and power level, and the changes are by no means as radical as those in the telecommunication switching stations. In part, this is attributed to the fact that there is no valid method for scaling, and development must be carried through with facili ties for investigation at the full level of power to which the apparatus may be subjected. Three of the main types of apparatus-circuit breakers, transformers and high-voltage convertors-have been selected for study from a typical substation at Dorsey in Manitoba, Canada, which receives d.c. power from the Nelson River scheme for use in the Manitoba network. Reference is made to the significance of electronic instrumentation as an essential service, and the technique of a light link telemetry, using fibre optics as the communication link, has been selected as a particularly effective means of obtaining data under high-voltage test conditions.