Testing of non-toroidal shape primary pass-through current transformer for electrical machine monitoring and protection

The monitoring of electrical machines is based on current measurement in most of the cases. For this purpose the use of current transformer is a common practice and currently the use of non-toroidal shape primary pass-through current transformers is increasing. Some problems in the monitoring and protection of large transformers and motors have been detected when this type of current transformer have been employed, with several cables per phase. The transient response of the current transformers is essential for the correct operation of the monitoring system. During the starting or in short-circuit condition, high current flows into the primary and secondary windings and as result large flux and electromagnetic forces are developed. This paper presents the advantages of testing non-toroidal shape primary pass-through current transformer with high current primary injection instead of secondary voltage injection as it is normally do.