Editing Current transformer (section)

{{Short description|Transformer used to scale alternating current, used as sensor for AC power}}
[[Image:Leistungsschalter-110KV.jpg|thumb|upright|A CT for operation on a 110&nbsp;kV grid]]

A '''current transformer''' ('''CT''') is a type of [[transformer]] that reduces or multiplies [[alternating current]] (AC), producing a current in its secondary which is proportional to the current in its primary.

Current transformers, along with [[Voltage transformer|voltage or potential transformers]], are [[instrument transformer]]s, which scale the large values of voltage or current to small, standardized values that are easy to handle for measuring instruments and [[protective relay]]s. Instrument transformers isolate measurement or protection circuits from the high voltage of the primary system. A current transformer presents a negligible load to the primary circuit.<ref name=SHEE11>Donald G. Fink, H. Wayne Beatty (ed), ''Standard Handbook for Electrical Engineers, Eleventh Edition'', Mc-Graw Hill,1978, 0-07-020974-X, pp. 10-51 - 10-57</ref>

Current transformers are the current-sensing units of the power system and are used at generating stations, electrical substations, and in industrial and commercial electric power distribution.