Some analysis focusing on the transient stability at the sending end of AC/DC hybrid system taking critical fault clearing time(tcr) as the inductoris are made and an Optimal Variable Aim Control(OVAC) strategy is proposed to improve its transient stability.

The fault critical clearing time was determined by the crossing point of the quadratic surface with the continuous fault trajectory.

It is also found the proportion of motor load has great impact on the critical clearing time.

The transient angle stability margin and critical clearing time are computed by FASTEST under different proportion of dynamic electric load model using in Henan Power Grid.

Two applications, calculating the critical clearing time and contingency ranking, are presented based on the approximated index.

A new nonlinear transformation is put forward in this paper,by which there is no poly value problem when the critical clearance time is determined; the general form of the movement equations in terms of Taylor.

A theorem to determine the critical clearance time is derived.

Critical clearing time (CCT) is one of the most important stable indices in power system transient stability analysis.

The formulae for SMIS are derived and verified by case simulation,the solution of critical clearing time (CCT) of three-phase short fault in MMS is theoretically discussed.