It is not possible to use line current directly for measurement and relaying purpose due to its high value and insulation problem. CURRENT TRANSFORMER is a piece of electrical equipment which converts line current values which are suitable for the devices to which is connected e.g. measuring instruments, meters, protection relays.

BASIC FUNCTIONS OF CTs ARE :

• To reduce line current to a value which is suitable for measuring instruments, relays etc.
• To isolate the measuring instruments, meters, relays etc. from line voltage of an installation.
• To protect measuring instruments against short circuit currents
• To sense abnormalities in current and give current signals to protective relays to isolate the defective system.