Electro-optic field sensor (EOFS) provides a non-contact method to measure both the transient and steady state voltage of transmission line. However, coupling effect of electric field generated by three-phase voltage distorts the results. Decoupling method need to be proposed. To measure voltage of transmission line, three EOFSs are placed under line of each phase. The electric field detected by EOFS consists of three components that generated by three phase voltages. The output of EOFS can be express as:U_out (t)=MU_line (t).The decoupling process is to calculate Matrix M. In this paper, two different methods are proposed using the parameter of steady state voltage compared with synchronous dtaa from CVT. One way is solved the equations in frequency domain and the other way is in time domain. The phase deviation and amplitude error of transient voltage during breaker operation process is corrected by applying the proposed methods. The time-domain method is affected dramatically by different sampling values and has poor performance for transient process. Two decoupling methods based on parameters of steady state voltage were proposed in this paper. The methods were verified by field experiments in a UHV AC substation. The frequency-domain method has better performance.

decoupling method,transient voltage,electro-optic field sensor,non-contact measurement