Empirical research in the distribution system security region(DSSR)of an actual distribution network is completed for the first time

and applied to the security analysis during the summer peak load. To begin with

the definition and method of DSSR is briefly introduced

in which the security assessment and security control method are improved according to the requirement of the dispatching department. Secondly

a distribution network that covers 4. 82 km2 with complete distribution automation in the core urban area of Tianjin is selected to calculate the security boundary

further verifying the existence of security boundary. Finally

security analysis of summer peak load is carried out based on DSSR

with the results compared with the existing security analysis report. The comparison shows that security boundary can describe the range of N-1 secure operation accurately and the results of security analysis of peak load of summer are in agreement with the actual situation.