Shunt reactors are installed on the long lines to reduce overvoltage. When the compensated line is opened to clear a fault, we find that the open-phase voltage does not disappear. A transient voltage waveform with a resonant frequency between 35Hz and 45Hz, can be seen which slowly reduces in magnitude. This transient phenomenon depends on the line parameters and the level of compensation. During the autoreclosing stage, the transient voltage will superimpose on the source voltage creating dangerous overvoltages along the line and on the shunt reactors. A controlled closing technique is one possible solution to the overvoltage problem. To do control closing it is necessary to analyze the voltage over the switching contacts, to predict voltage shape and to identify an optimal switching instant. In this paper very accurate algorithm for voltage signal modelling is presented. The paper concludes with presentation of the representative practical results obtained in modelling and predicting a voltage signal recorded on a 765kV line with shunt reactors. The results show that the novel technique gives accurate signal modelling and prediction under practical conditions.