Electronic Tap-Changing Stabilizers for Medium-Voltage Lines Optimum Balanced Circuit

Thyristor-based onload tap-changing ac voltage stabilizers can replace mechanical tap changers associated with transformers feeding medium-voltage (MV) lines (typically 69 kV primary, 34.5 kV line, 6.3-50 MVA), thus avoiding frequent contacts revision. As shown in a previous paper, the topology using a compensating transformer in the main circuit and a multiwinding coil in the commutating circuit give good technical and economical results independent of the coil operation mode (shared, nonshared, and mixed load). This second paper focuses on this topology and defines the criteria for an optimum design and the synthesis formulae that give the definition parameters of the components as a function of the equipment characteristics. Numerical results are added for a typical 10-MVA stabilizer. One of the best circuit solutions (single switch comb, mixed load, auxiliary short-circuit winding), which does not need a series association of thyristors, is developed in detail. Final synthesis formulae, effective power of the transformers and coil, and summatory of thyristors I·U products for all three operation modes are contrasted in a table as the final step of the iterative analysis and synthesis cost-comparative method followed along the research.