We have carried out an analytical study of the operation conditions of AC transmission lines with series compensation devices (SCDs). We have established that the application of capacitive compensation is associated with the limitations determined by voltage deviations at the intermediate points of the line. Significant reactive power generated by capacitance requires the use of shunt compensation. The obtained results indicate the disadvantages of using SCDs with a large capacitive conductance, since the possibilities for increasing the transmission capacity of such an SCD are limited by the voltage drop across the capacitance. If it is necessary to compensate the inductance of long-distance overhead lines, it is advisable to apply several SCDs with a reduced capacitance in each of them. We have analyzed the operation conditions of one of the well-known compensated power transmissions with several SCDs. It is shown that the ability to control reactive power when changing line loading and the ability to control the voltage settings of the CSR contribute to a significant increase in their transfer capability.