SINGLE-STAGE AMPLIFIER-AIDED CURRENT TRANSFORMERS POSSESSING SMALL RATIO ERRORS AT 60-HZ

Two directly coupled electronic techniques are described which reduce significantly the burden seen by a single-stage toroidal current transformer. Almost all the power is supplied by an electronic power amplifier so that magnetizing current within the transformer is extremely small. Magnetic cores of small physical size may be used with small numbers of turns. Measured ratio errors at unity ratio are approximately 10 parts per million or less at 60 Hz provided certain restrictions are satisfied with respect to dc offset voltages within the electronic amplifier used. This particular technique lends itself to the use of modern packaged linear amplifiers which may be adapted for power use. Directly coupled electronic circuitry enables the techniques to be used at lower frequencies. Ratio error measurements are described and comparison made between the actual ratio errors obtained experimentally and the theoretically predicted values. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.