Current transformers

  Current transformer is a transformer with primary winding connected to curret source and secondary winding connected to measurement or protective devices with small internal resistance.
  Current measurement transformer is a transformer, designed for conversion of a current to a level suitable for measurement. Primary winding of a current transformer have to be connected in series with the measured alternative current, and the gauges are to be connected to the secondary one. The current flowing through the secondary winding of the current transformer, is proportional to the current flowing through its primary one.
Current transformers are widely used for measurement the electric current and as gauges for relay protection devices of electric power systems, thus high accuracy requirements are superimposed on them.
  Current transformers provide measurements safety by insulating measurement circuits of high-voltage (up to hungreds of kV) primary circuit.
There are high demands of precision for current transformers. As a rule, the current transformers are performed with two and more groups of secondary windings: one of them usually connected to protection devices, and another one - more precise - for connection a counting and measurement means (for example, electric meters).