The paper presents the results obtained from a study of flexible reactive power compensation systems. The aim is to evaluate the application of flexible reactive power compensation systems for industrial consumers and to develop stability and quality comparison for two fundamentally different high speed reactive power compensation systems. The first of them is system with constant volume of compensation capacitors and in parallel to them regulated by thyristors reactors; the second one is so named STATCOM system with modulated by transistors parameters of reactors-capacitor circuits. Both investigated systems can react very fast to changes of power relations in compensated load circuits, i.e. they are a flexible compensation systems. Comparison of the both systems is reduced to investigation of their response time to load power component deviations.