Low Tension Current Transformers

Low Tension Current Transformers are used for measurement andor protective applications in 660V Class. In Measuring Current Transformers (Refer TABLE- 1) main concern is the accuracy of the secondary current over a wide operating range. Typically the errors are guaranteed to be within specified limits. The nature of errors are current (Ratio) error and phase displacement. Metering current transformers are specified by (1) a burden and (2) accuracy class.
Protective Current transformers (Refer TABLE-II) are specified by (1) a burden (2) accuracy class and (3) accuracy limiting factor. In other words the errors of the protective current transformers at the rated full loaded current as well as at a current given by the accuracy limit factor times the full load current are specified. There exists a class of protective current transformers for special purpose application known as class PS CTs. These are mainly intended for use in applications where the required characteristics of the current transformers cannot be conveniently expressed in terms used for class 5P, 10P and 15P current transformers. The knee point voltage, exciting current and secondary winding resistance are so dependent on the protective gear involved. The manufacturers of protection gear stipulates the requirements in terms of minimum knee point voltage and maximum exciting current. The current transformers of class PS type are of low reactance type since the core is made up of jointless ring type (spirally wound toroidal type) cores and secondary turns are substantially evenly distributed along the whole length of the magnetic circuit.