Generalized Circle Diagrams and Their Application to Protective Gear

The common underlying theory of generally used systems of protection involving comparison of two vector quantities is derived by coaxial (bipolar) circles in the complex plane, where amplitude or phase comparison can be used interchangeably to produce any desired circle or straight line characteristic. Practical departure from ideal comparison, resulting from relay power consumption, is considered, and the relationship between this analysis and two currently used methods of distance relaying is pointed out. The basic circuit of a commonly used pilot wire scheme is analyzed and its characteristic considered, and the effect of long pilots with distributed constants is indicated.