Abstract :
The design, construction, and performance of two nearly identical, multirange current transformers for operation 400 Hz to 10 kHz and with errors of only a few ppm are discussed. A general discussion of the parameters that influence the performance of single-stage transformers and their consideration in effecting minimum errors throughout a wide frequency band is included. Construction of the two standards having consecutive ratios 1 to 1 to 6 to 1 and operating at a rated secondary current of 5 amperes is described. Circuit diagrams are used to describe 1) the self-calibration circuit for measuring the errors of the 1-to-1 ratios and 2) the (N+1) circuit together with an auxiliary circuit for measuring the errors of ratios> 1. Balance equations are derived in the Appendix. Measured values are presented; included are the results up to 16 kHz obtained at the National Research Council, Canada, during an international comparison and described in a companion paper [6]. The effects of polarization at low frequencies are emphasized by utilizing the 400 Hz data together with information obtained in supplementary experiments; also the role of winding and interwinding capacitances and the necessity for a more explicit definition of current ratio at the higher frequencies is highlighted.
