Experience with computer-aided graphical analysis of sudden-short-circuit oscillograms of large synchronous machines

In a companion paper, computer programs are proposed for automating the analysis of sudden-short-circuit oscillograms in accordance with present IEC and IEEE standards. In this paper, we further illustrate the capabilities of computer-aided graphical methods with a view to their incorporation into modern testing practices. Using synthetic short-circuit data obtained from an exact solution of the network equations of known machines, it is first shown that use of the proposed software leads to satisfactory parameters in a number of realistic situations, including those where sub-subtransient effects are present. When faced with real data, it is shown that pre-filtering, without phase distortion, is often necessary and some useful tools are suggested for carrying this out. A thorough investigation of the automatic graphical method applied to three machines, differing widely in design, suggests that the new software is robust enough to be used on a regular basis, either in the field or in the design office. Using the Takeda & Adkins K-factor, derived graphically from the field current oscillogram, even a full second-order network is possible, matching the underlying phenomena, as seen from both the rotor and stator