Larger buildings may be supplied with a medium voltage electricity supply, and will required a substation or mini-sub. What is the main item of equipment contained in these?

Answer: Option A

The transformer is used to transform a medium voltage supply to a low voltage supply, e.g. from 11 000 V to 400 V. A transformer is rated in KVA, kilo-Volt-Amps, which is a measurement of electrical power.