three phases

Current transformer and voltage transformer . This transformers are actually measuring instruments which measures the quantity of current and voltage coming out of the substation.

use of CT

Prefabricated power distribution substation

Its basically a whole 11kv substation but in one unit. It contains a transformer, ring main unit, fuse board and circuit breakers etc. It still uses as much space as a normal substation that houses a separate transformer, ring main unit etc but is easier to transport and is probably cheaper.

Primary substation - when the transformer is HV/MV or MV/MV. e.g. substation designed for 132kV/33kV or 230kV/22kV or 33kV/11kV etc

stepped down for MV distribution (mainly for utilities and heacy industries)

Secondary substation - when the transformer is HV/LV or MV/LV. e.g. substation designed for 11kV/400V or 6.6kV/400V etc

stepped down for LV distribution (mainly for residential, commercial) sometime referred to as a kiosk substation.