An Investigation of Electromagnetic Transients for a Mixed Transmission System with Overhead Lines and Buried Cables

An electromagnetic transient study has been performed based on a practical 500 kV mixed transmission system. The system has overhead lines, submarine cables and underground cables. An exact expression of earth-return impedance for submarine cable has been developed. A new equivalent homogeneous earth method (EHEM) is also proposed based on the exact formula. The influences of air, seawater, seabed, wired armor structure and multi-layer seabed on series impedance and modal propagation constants of submarine cable are investigated. A novel modeling procedure on parametrical side of mixed transmission system is proposed in this paper. Moreover, the input sequence impedances of mixed transmission system are studied based on traditional Line / Cable Constant routines and the new method. Transient simulations are also performed using classical and new methods. The results are further validated with recently proposed MoM-SO technique.