Design of Substation Earthing Network with Frozen Soil Verification
Studies and tests have shown that the resistivity of soil increase 5 to 1000 times when it condenses into perma-frost.In winter,the soil gradually forms a high resistance layer downwards along vertical direction until the permafrost depth;in spring,the formed high resistance layer dissipates downwards.In the process of this cycle,the soil resistivity within the depth of the permafrost undergoes dramatic changes.And then,the impact that the performance of the substa-tion earthing network by frozen soil will be significant.Currently,there are few relevant studies and applications in engi-neering design.Langfang Liulin 220 kV substation,as a key project,adopts a layered soil model,equivalent to actual fro-zen soil,and carries out the quantitative evaluation and verification of the performance of the earthing network for the first time.The test shows that it is feasible to adopt the layered soil model equivalent method,and it is necessary to carry out permafrost calibration and assessment,involving safety assessment.