For UHV and long-distance transmission lines with obvious distribution parameter characteristics

the distributed capacitance current has a great influence on the sensitivity and reliability of the traditional current differential protection based on Kirchhoff current law. Based on Bergeron model

the protection criteria are constructed by using the current calculated from one end voltage and current to the other

and the current calculated from the voltage and current at both ends to the midpoint respectively. And the pilot protection scheme with multi-point joint decision is formed. The protection criterion is constructed by ratio

and the ratio will be 1 theoretically under the outside fault

which is easy to construct the protection setting value and is less affected by the fault resistance. A large number of simulation results show that considering the distribution parameter characteristics of extra-long UHVDC transmission lines

the influence of distributed capacitance current on the protection criterion can be further reduced by the criterion of multi-point joint judgement

and the reliability of differential protection of longdistance transmission lines can be improved.