An instrument for complete symmetrical-component analysis

Established methods for the resolution of an unbalanced system into positive-and negative-sequence components are extended to give information about their relative phase-displacement. The method developed depends on the inherent property of dynamometer instruments that, for given currents in the coils, the deflection is proportional to the cosine of their phase difference. A dynamometer instrument of ordinary design was modified simply for the purpose by separating the coils and connecting the ends to external terminals, two similar resistance-capacitance networks being added. If it is assumed that the zero-sequence component is absent, or has been eliminated, three readings r1, r2 and r12 and one unrecorded test of a qualitative nature are sufficient for a complete analysis. The test serves to determine the sign of the phase angle, the sequence components r1 and r2 are given directly, and the expression cos ¿=r122/(r1r2) enables the phase angle to be found. The only calculation is very simple, and the solution can be obtained quickly from nomogram.