Vibration frequency response function can be calculated, thereby characterizing the system. This technique is used in the field of experimental modal analysis to determine the vibration characteristics of a structure. The simple mass–spring–damper model is the foundation of vibration analysis, but what about more complex systems? The mass–spring–damper model described above is called a single degree of freedom (SDOF) model since the mass is assumed to only move up and down. In more complex systems, the system must be discretized into more masses that move in more than one direction, adding degrees of freedom. The major concepts of multiple degrees of
Per-unit system use the nominal voltage 138 kV as the base voltage formula_23. We then have: If, for example, the actual voltage at one of the buses is measured to be 136 kV, we have: The following tabulation of per-unit system formulas is adapted from Beeman's "Industrial Power Systems Handbook". It can be shown that voltages, currents, and impedances in a per-unit system will have the same values whether they are referred to primary or secondary of a transformer. For instance, for voltage, we can prove that the per unit voltages of two sides of the transformer, side 1 and side 2,