Location of Series Capacitors in High-Voltage Transmission Systems [includes discussion]

Over-all system economy can be improved by means used specifically to increase the power limits of high-voltage, large-conductored transmission lines.1-24 Important methods for increasing the stability limits of high-voltage transmission systems are: 1. Intermediate switching stations, with and without series capacitor compensation. 2. Intermediate systems. 3. Automatic circuit reclosing. 4. Switched shunt capacitors and reactors. 5. Generator excitation systems. This paper reviews and compares four possible methods of applying series capacitors, together with intermediate switching stations for improving the transient stability limit of high-voltage systems. The function of intermediate switching stations to improve the stability limits of transmission lines is primarily that of removing transmission line faults by disconnecting a smaller line section with a correspondingly smaller shock than if intermediate switching stations were not used. Detailed studies of intermediate switching stations have been previously reported24 which indicate that they can be economical for lines as short as 50 miles. Series capacitors reduce the over-all line reactance, and hence allow a larger stable transfer of power. Series capacitors can also be applied to obtain better load division21,22 on parallel lines having different conductor resistances and/- or different lengths, although series capacitors applied for this purpose show only marginal economic benefits. In general, series capacitors appear to be economical for increasing the stability limit of lines about 200 miles or longer. There has been, however, some divergence of opinion as to the most economical location for the series capacitors in the transmission system.