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This paper presents a new decoupled-quadratic load flow (DQLF) approach for adjustment of parameters of static VAr compensator (SVC). The DQLF model can calculate effectively the SVC susceptance and resulting firing angle using a simple quadratic equation derived using real and reactive power injections at the SVC bus. The resulting quadratic equation, in terms of bus voltage magnitudes can easily evaluate system voltage stability margin. The model makes use of conventional fast decoupled load flow (FDLF) algorithm for calculation of voltage phase angle corrections. The bus voltage magnitudes at all load buses are calculated using a quadratic equation derived using real and reactive power injections at the buses. The proposed approach eliminates the formation and modification of B" matrix in FDLF models and offers considerable saving in the execution times. It is found to be very reliable for Q-adjusted studies and ill-conditioned cases. The DQLF model offers 50% faster convergence than FDLF model, when applied to large systems, having a large number of generator buses (DQLF model is tested on IEEE 118 bus system). The validity of the proposed algorithm for SVC parameter adjustment is tested on IEEE 14 bus system. The stability margins are evaluated using the proposed quadratic equation, and compared with traditional Q-V sensitivity model. The 14th bus is found more prone to instability. An effort is made to control the bus voltage at 1.06 pu. The final parameters Bsvc and firing angle α obtained using DQLF model are compared with those obtained using Newton Raphson (NR) and FDLF models and found to be same.