This paper presents a frequency-scan analysis of a large medium voltage distribution system. The objective of this study is to determine the frequency characteristics of Currents and voltages produced in loads substations and ill distribution Substation by the frequency dependent Current sources located in loads substations. An analytical relationship for calculating the potential of medium voltage point is deducted. In order to differentiate harmonic Currents due to actual Sources from harmonic currents due to resonance involving a capacitor bank an SPICE simulation has been performed. Useful conclusions for analyzing the propagation of harmonic distortions are derived.