Current transformers (CTs) are designed for connection in the primary circuit
(either in series or around the primary circuit). The secondary current of
the transformer bears a known relationship with the primary current. Any
change in the primary current is refl ected in the secondary circuit. Relays,
meters, and other devices are connected to the secondary terminals of the
CTs. CTs are made in many different ratios, different voltage insulation systems,
and for different environmental conditions such as indoor or outdoor
use. Generally, the following types of construction are used for CTs.