In order to satisfy the demands of DC de-icing of optical fiber composite overhead ground wire（OPGW） and solve questions such as circulating current loss and its liability in suffering from lightning stroke and broken

the grounding method of OPGW must be changed from the current commonly-used method of being grounded at every towers to being grounded at one tower. OPGW would be connected with tower by ground wire insulator

which should be equipped with protective discharge clearance. Consequently

we put forward an idea that the clearance distance should not only satisfy the requirements of withstanding the induced voltage and the de-icing voltage

but also ensure reliable breakdown at lightning voltage. Moreover

we calculated and experimentally researched the electrical characteristics of discharge clearance at normal operation

on de-icing

and in lightning conditions

respectively. Results indicate that discharge clearance should be set from 20 to 100 mm to withstand power frequency induction voltage. Furthermore

discharge clearance should be set more than 60 mm to withstand DC de-icing voltage

which is-22 k V at most. Considering the dispersion of clearance discharge

the clearance should be appropriately increased. The recommended value of discharge clearance is from 70 to 80 mm. The lightning impulse discharge voltage of such clearance is generally not more than 100 k V. However

as transmission line is struck by lightning

overvoltage on insulator and clearance is 885 k V at least

even up to a few MV. Clearance can be broken down reliably to ensure safety of insulator. Research results can provide a theoretical support and data support for OPGW de-icing insulation reconstruction.