It is not possible to use line current directly for measurement and relaying purpose due to its high value and insulation problem. CURRENT TRANSFORMER which is widely known as 'CT' is a piece of electrical equipment which converts line current ( primary current ) in to small standard current values which are suitable for the devices to which it is connected e.g. measuring instruments, meters, protection relays.

It is not possible to use line current directly for measurement and relaying purpose due to its high value and insulation problem. CURRENT TRANSFORMER which is widely known as 'CT' is a piece of electrical equipment which converts line current ( primary current ) in to small standard current values which are suitable for the devices to which it is connected e.g. measuring instruments, meters, protection relays.