what is pt and ct in electrical system give full detail?

Answer 1

Both are transformers
PT- POTENTIAL TRANSFORMER
and
CT- CURRENT TRANSFORMER
A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling, without requiring relative motion between its parts. A transformer comprises two or more coupled windings, and, in most cases, a magnetic core to concentrate magnetic flux. A changing voltage applied to one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings.

A current transformer (CT) is a type of "instrument transformer" that is designed to provide a current in its secondary which is accurately proportional to the current flowing in its primary.
Voltage transformers (VTs) or potential transformers (PTs) are another type of instrument transformer, used for metering and protection in high-voltage circuits. They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential.
source: wikipedia

Answer 2

Power Transformer and Current transformer.

Answer 3

potential transformer : steps down the voltage so that it can be measured with a voltmeter.
current transformer : steps down the current so that it can be measured with ammeter.