This paper presents a method of enhancement of transmission capability limit using system damping resistor (SDR) and series - shunt capacitors (SC and ShC). The SDR is very effective for short distance transmission lines such as 50km or so. The SDR is small in capacities for transmitted power and the durations of switching time are around 0.5s. Experiments are carried out for the determination of optimal size and switching time of the SDR for about 50, 100 and 150km transmission lines. The effectiveness is certified by experiments using an artificial transmission line model. For long distance transmission lines, experimental results indicate that the transmission lines compensated by series capacitor are effective.