The surface charge accumulation on insulators is one of the important factors that limit the development of high-voltage direct current (HVDC) gas insulated transmission line (GIL)

and the accurate measurement of surface charge is the basis to explore its physical mechanism. In this paper

to solve the problem of measured potential attenuation during on-line measurement of an electrostatic capacitance probe

a surface potential restoration algorithm (SPR) is proposed

and the effectiveness of the proposed algorithm is verified by the equivalent circuit simulation and the experiment. The results show that: the continuous charge leakage on the induction electrode during on-line measurement will cause the probe output potential to attenuate with time

and the measurement error caused by this cannot be ignored. Meanwhile

it has been proved that the proposed SPR algorithm can effectively restore the surface potential. The maximum error between the restored value and the real value is about 3.4%

and the minimum error is only 0.6%. In addition

the surface potential restoration accuracy of the SPR algorithm is negatively correlated with the ratio between the sampling interval Δt and the probe time constant τ

that is

the smaller the value of Δt/τ

the higher the surface potential restoration accuracy. This study can provide a reference for the on-line measurement technology of DC GIL insulator surface charge density.