HIGH-CURRENT HIGH-PRECISION OPENABLE-CORE AC AND AC DC CURRENT TRANSFORMERS

The application of an electronic, technique, which greatly increases t he apparent permeability of the magnetic core of a current transformer , to high-current high-precision open-able-core ac and ac/dc current t ransformers is described. The openable-core ac/dc current transformer can be used to measure accurately alternating current only or direct c urrent only, or both alternating and direct currents simultaneously. T est results of two prototypes, 5000 A/5 A openable-core ac and 2000 A/ 1 A openable-core ac/dc current transformers, indicate an ac current m easurement accuracy of both types of transformers of the order of 10 p pm and a dc current measurement accuracy of the openable-core ac/dc cu rrent transformer of better than 100 ppm.