What are the application of current transformers?

Current transformers are used to monitor the current flow through larger diameter wires. They are rated in ratio of 1: to the ampacity of the wire they are monitoring. They are used in electrical distribution services over 200 amps. Maximum current produced is 5 amps. eg. A conductor has a maximum capacity of 500A and you want to see how much current is going through the wire at any one time. You have a meter mounted in a control panel with main graduations of 100A, 200A, 300A, 400A and 500A. The same hold true on a distribution service where the CT is connected to the meter base. The specs on the meter says full scale deflection 5 amps. The CT is mounted on the conductor like a do-nut and has a ratio of 1:500. 500A through the conductors induces 5 amps in the CT, full scale deflection of the meter to the 500A position. The current through the CT is in direct porportion to the current through the conductor. 250A through the conductor, induces 2.5 amps in the CT, half deflection of the meter to a position halfway between 200A and 300A, or 250A.