This paper describes the operating principles, design and field performance of two-level, three-leg device commutated current source converter (CSC) topology based Static Synchronous Compensator (STATCOM), which is developed for medium voltage industry applications. In the paper, the relationship between the reactive power and the control variables is obtained, harmonic minimization techniques applicable to CSC are investigated, and then Selective Harmonic Elimination Technique is applied for the elimination of the 5th, 7th, 11th and 13th harmonics in CSC line current. The design principles of the input filter are also set out. Considerations for optimum sizing of STATCOM in common industry applications are described with the design objective of maximum utilization of power semiconductors. Two CSC based STATCOMs, which are rated at +/- 500 kVAr and 0-1500 kVAr capacitive are implemented and applied to industry. Field results are also given in the paper in order to validate the operating principles and design criteria. (C) 2010 Elsevier B.V. All rights reserved.