Harmonic voltage amplification in a distribution network due to resonance of transfer impedance to the EHV transmission

The region „Unterengadin“ is situated in the southeast of Switzerland in the middle of the Alps. The regional distribution networks are fed from the 380kV substation „Pradella“ which is connected via a 380 kV overhead line to Sils and the Swiss as well as the European EHV transmission grids. In the year 1991 the EHV transmission grid has been extended with a double circuit overhead line from „Pradella“ to „Westtirol“ in Austria (FIG. 1).