TY JOUR TI Underground Three-Phase Power Transmission Line KW Underground power line KW capacitive current KW reactive power KW three-phase power supply system KW long line theory KW power losses JO Bulletin of scientific research results AU Siukaev, T.Z. AU Dudin, B.A. AU Ben'yash, Y.L. AU Shevlyugin, M.V. AU Varicheva, V.V. PY 2025 IS 2025 PB FSBEI HE "Emperor Alexander I St. Petersburg State Transport University"