From weather-related uncertainty to geometrical errors of OPL design, numerous factors contribute to the variations of impedance and conductance. Still, an unambiguous judgment can be made on how such variations could affect the transient stability does require additional simulations and computational experiments. This research seeks to evaluate how deviations in the parameters of OPL equivalent circuits could affect the transient stability of generators. To that end, the paper proposes a primitive trinodal test system for simulating random deviations in OPL equivalent circuit parameters so as to run multiple simulations of transients. Step One is to independently analyse each parameter in terms of how it affects the critical fault clearance time. Step Two is to simultaneously measure the line conductance and impedance and to monitor the curves of the test-network generators. The final step is to computationally analyse the collected data so as to find the controlled values as a function of equivalent-circuit parameters. Experimentation has revealed two patterns; first, only random deviations in reactance significantly affect the stability. Second, as found at Step Two, random deviations result in significant uncertainty and scatter of the parametric curves. Thus, the research demonstrates that neglecting the possible deviations in equivalent-circuit parameters in the first approximation does affect simulation results.