State perception of long-span 10 kV cable lines is one of the critical issues in building intelligent distribution networks. Digital twin (DT)

which can map the physical status of equipment in real-time

has received extensive attention. However

traditional modelling methods cannot meet the requirement of long-span complex DT's real-time computation and scalability. In order to reduce the modelling cost and improve the calculation speed

a modular DT modelling method for cable lines based on real-time temperature field inversion is proposed. The authors develop a modular reduced-order modelling method that applies to long-span 10 kV cable lines. Combined with the temperature field inversion

a DT inversion algorithm is proposed to evaluate the transient temperature field and contact resistance inside cable lines

which has been used to evaluate the emergency load capacity. Finally

temperature rise tests verified the DT inversion algorithm's correctness. The operating status of cable lines was evaluated through the modular DT

and the emergency time and emergency ampacity were calculated. The result shows that the new method meets the real-time and high-precision requirements of DT calculation in actual operation scenarios. It can be easily extended to cable lines of different voltage levels.