To meet the requirement of calculation time for on-line transient security and stability assessment

an on-line transient security and stability contingency screening method based on margin and mode estimation is proposed. According to the margin and modes information of each contingency in previous assessment results

including transient power angle stability

transient voltage security

transient voltage stability

and transient frequency security

and combining the power flow change

in service or out of service information of the relevant components associated with the security and stability modes of each contingency

the transient security and stability margin of each contingency under the new on-line transient security and stability evaluation is estimated

and the corresponding security mode is determined. Thereby

the contingency subset

which needed to be calculated in detail can be screened from the complete contingency set in the on-line transient security and stability evaluation. According to the simulation analysis of actual power network data

the validity and practicability of the proposed method can be verified.