High-current high-precision openable-core AC and AC/DC current transformers

The application of an electronic technique, which greatly increases the apparent permeability of the magnetic core of a current transformer, to high-current high-precision openable-core AC and AC/DC current transformers is described. The openable-core AC/DC current transformer can be used to measure accurately alternating current only or direct current only, or both alternating and direct currents simultaneously. Test 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 measurement accuracy of both types of transformers on the order of 10 p.p.m. and a DC current transformer of better than 100 p.p.m