Isolating current transformer for accurate measurements - has integrating circuit and control winding for rapid change of magnetisation

摘要

The transformer is in two sections. The compensating winding is switched in alternate half cycles by solid state switches with alternating polarity across a d.c. supply. The switching only takes place during the short intervals when the current to be measured is changing rapidly. At such times the integrator is switched off. When the compensation current is very small the switch between the common point of the compensating windings and one input of the integrator turns on and an integration over a time period takes place. With low magnetising current and high permeability the leakage flux is very small during the integrating time. Thus primary and secondary windings may be spaced well apart to give the required galvanic separation.