Nyquist frequency signal, whereas "Nyquist frequency" is a property of a discrete-time system. When the function domain is time, sample rates are usually expressed in samples per second, and the unit of Nyquist frequency is cycles per second (hertz). When the function domain is distance, as in an image sampling system, the sample rate might be dots per inch and the corresponding Nyquist frequency would be in cycles/inch. Referring again to Figure 1, undersampling of the sinusoid at 0.6 f is what allows there to be a lower-frequency "alias", which is a different function that produces the same set of samples. That
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,