Free Download | Extra High Voltage (EHV) A.C.

Extra High Voltage (EHV) A.C. transmission may be considered to have come of age in 1952 when the first 380–400 kV line was put into service in Sweden. Since then, industrialized countries all over the world have adopted this and higher voltage levels. Very soon it was found that the impact of such voltage levels on the environment needed careful attention because of high surface voltage gradients on conductors which brought interference problems from power frequency to TV frequencies. Thus electrostatic fields in the line vicinity, corona effects, losses, audible noise, carrier interference, radio interference and TVI became recognized as steady state problems governing the line conductor design, line height, and phase-spacing to keep the interfering fields within specified limits. The line-charging current is so high that providing synchronous condensers at load end only was impractical to control voltages at the sending-end and receiving-end buses. Shunt compensating reactors for voltage control at no load and switched capacitors at load conditions became necessary. The use of series capacitors to increase power- handling capacity has brought its own problems such as increased current density, temperature rise of conductors,  increased short-circuit current and subsynchronous resonance. All theseare still steady-state problems.