A voltage measuring system with an optical fibre cable comprising: a first electric terminal (11, 17, 24); and a second electric terminal (11, 17, 22); an optical fibre cable (10, 20) positioned in the electric field formed between said first (11, 17, 24) and said second terminal (11, 17, 22); a laser source (40) which provides an optical signal to said optical fibre cable (10, 20); means (15, 28) for rotating the state of polarization (SOP) of the optical signal passing through said optical fibre cable (10, 20); a coherent receiver (41, 42) to receive a reflected optical signal coming from said optical fibre cable (10, 20) and measure the electric voltage present between said first terminal (11, 17, 24) and said second terminal (11, 17, 22), by measuring the phase shift Δφ induced in said optical fibre cable (10, 20) due to electro-optic Kerr effect by the voltage applied between said first electric terminal (11, 17, 24) and said second electric terminal (11, 17, 22); means for measuring the temperature of said optical fibre cable (10, 20), to allow the dependence of the Kerr effect on temperature variations to be compensated in real time.