A potential transformer PT is also called voltage transformer VT. Just like a distribution transformer, a potential transformer PT steps down high voltage level to a standardized value, such as 100 V or 110 V, to provide an electrical signal to upstream or downstream relays, energy meters and control devices, while offering a stable power supply to secondary circuit and an electrical isolation between primary circuit and secondary circuit.
On functional, an current CT steps down primary current to a standardized value, but an potential transformer PT steps down primary voltages to a appropriate value, while providing power supply to secondary devices on an electrical panel such as protection relay, or control units.
On structural, transformer turns ratio is contrary between a current transformer CT and a potential transformer PT. In a current transformer CT, the number of primary winding turns is smaller than the secondary winding, because of energy formulas in terms of current and voltage. Meanwhile, in a potential transformer, the number of primary winding turns is larger than the secondary winding.
Additionally, a current transformer CT parallels the distribution line, but a potential transformer PT series with the line.
