Below we have a potential transformer used to measure high AC voltage:
The potential transformer (PT) is used to reduce the line voltage to the level which is acceptable for measurement, control and protection circuits. The relation for voltage transformation is:
The line voltage is reduced based on the ratio of the number of turns of secondary winding to that of the primary winding (turns-ratio).
When a potential transformer is connected to a live system on the primary side, its secondary behaves as a voltage source. Thus, care must be taken not to short circuit the secondary terminals of the PT; otherwise, the resulting high short-circuit currents may damage the PT.