Using AC Underground Cable for Long Distance Power Transmission

The charging current in underground cables imposes a serious practical limit to the transmission length. This paper proposes half-wavelength plus (lambda/2(+)) transmission method for underground cables to extend the transmission length to distances exceeding the electrical half-wavelength. The lambda/2(+) transmission method has been proposed previously for overhead lines. But, when this concept is applied to AC underground cables, we can observe three distinct and interesting characteristics: 1) Underground cables offer much shorter and more practical physical transmission distance than overhead lines; 2) Underground cables are more suitable for a medium voltage transmission (50-209 kV); and 3) No overvoltage issues exist along the cable length. Additionally, this paper presents a case study of 360 miles, 115 kV, 270 MW underground cable system and verifies the concept through simulation.