Anomalous power line carrier signal propagation on the Monopolar Cahora Bassa HVDC lines

This paper presents an analysis of the half-wavelength resonance phenomenon observed in the power line carrier system of the Cahora Bassa /spl plusmn/533 kV HVDC scheme. (Signal injection is achieved by means of differential coupling to the pole conductor and insulated shield wire on each of the two monopolar lines.) By means of the ABCD parameter equations, it is shown how and why the capacitance of the shield wire insulator causes complex resonances over a narrow band of frequencies (in the 350 kHz range) for which the tower spacings correspond to half a wavelength. It is also shown how the histogram of tower spacings for a given line may be used to calculate the total additional attenuation caused by the resonance.