Recently, an intelligent substation by the L-coupling static synchronous compensator integrated with a primary tapped transformer (L-STATCOM PTT) has been developed to perform multifunction operations, including stable power supply and desired power quality. While previous works mainly focus on current quality, the cost-effective compensation of voltage quality is still not involved. This paper firstly formulated the mathematical model of voltage compensation to reveal the compensation mechanism, and determine the required inverter rating and reasonable dc voltage for acceptable performance. Then its power rating reduction under different voltage drops has been mathematically revealed compared with conventional STATCOM. Furthermore, by considering the potential differences in IGBT switching time and collector-emitter on-state resistance, a more generalized and practical power loss model based on scaling laws is formulated. The proposed voltage compensation method can reduce compensator rating by 28.1% and power loss by 12.2% at the 10% voltage drop. Simulation and experiments are performed to prove the validity and effectiveness of the proposed topology over cost-effectiveness and load voltage support.