Difference between...!!!!

Difference between CT and PT

Current Transformer 

The secondary of a C.T can not be open circuited on any circumstance when it is under service. 

The primary winding of the CT is connected in series with the line carring the current to be measured. Hence it carries of the full line current. 

Potential transformers are used in usually in industrial and power plant settings to reduce the AC voltage of a power line to a lower value (typically 120 or 70 volts full scale) for instrumentation purposes. They are low power, have accurate voltage ratios and good galvanic isolation to isolate the instrumentation (and the operators) from dangerous voltages and power. Potential transformers can be wire-wound like a small power transformer or for very high voltages can take the form of a capacitive voltage divider or can exploit the electrical properties of optical materials. 

Transformers designated as current transformers have far more limited uses. Current or current sense transformers only lower current for use in meters and measuring devices, with little regard for power or voltage changes.

Potential transformer 

The secondary of a P.T can be open circuited without any damage being caused either to the operator or the transformer. 

The primary winding P.T is connected across the line of voltage to be measured. Hence the full line voltage is impressed across its terminal.

Current transformers are used to scale a large AC current which can be 10s of thousands of amps or more to be measured to a lower value, typically 1 or 5 Amperes that does not require heavy wires to carry the full current flow to be measured into the instrumentation. They are low power, do not disturb the current to be measured, have accurate current ratios, and like potential transformers, good galvanic isolation to isolate the instrumentation (and the operators) from dangerous voltages and power. 

Potential, power, or voltage transformers change commercial power from generators to high voltage and low current for nationwide distribution. Substations use similar transformers in reverse to reduce the voltage and increase the current to usable levels.