Abstract: Development of smart substation gives rise to the high requirements on telesignal and SOE resolution of measurement & control devices. A deep analysis is made on the abnormal phenomenon occurring in the process of testing telesignal and SOE resolution of measurement & control devices. Duo to the limit of the telesignal’s time tag that the smallest unit is in millisecond level, the requirement that the measure & control device’s telesignal and SOE resolution be less than 1ms cannot be totally satisfied in theory. During testing the damped oscillation wave of EMC，the causes for the telesignal and SOE resolution error is theoretically proved by simulation, that is: a decaying DC component with the initial value of 220 V is coupled into the circuit of the telesignal 2 after the telesignal 1 acts, which results in the telesignal 2’s action in advance. Finally, according to the characteristics of damping oscillatory wave experiment, a decoupling scheme is proposed, which can avoid the interaction between the telesignal circuits by changing the testing wiring that the telesignal 1 and signal 2 are plugged into different power circuits respectively.

Key words: measure & control, telesignal, SOE, EMC, differential mode interference