72-pulse gate turn-off thyristor based voltage source converter (GTO-VSC) topology having a number of 12-pulse VSCs as elementary unit together with fundamental frequency mode of GTO gate control are widely used in STATCOM for dynamic reactive power compensation in electrical network. A 72-pulse topology generally produces an AC output voltage waveforms which contain 35th, 37th, etc. harmonics and hardly find its application due to higher total harmonic distortion (THD) level. In this paper, a new model of 3-level, 72-pulse, 500kV, +100MVAr STATCOM employing 6x12-pulse GTO-VSCs, fundamental frequency gate switching, PI-control methodology, DC capacitor as an energy storage and two stages of magnetics is designed and simulated to attenuate harmonics of the order of 35th, 37th, 73th, 75th etc. by Sim Power Systems toolbox in MATLAB environment. The operating performance of the compensator is studied for regulating voltage and power factor correction in electrical network and results show the model acceptable for power system applications.