The interphase short circuit caused by core rod brittle fracture of suspension composite insulators on 220kV Ping-He line was analyzed.Strain insulators with single string

connection design without grading ring

early production composite insulators with manufacturing defects

and acid nonresistant core rod are main causes responsible for the fault.Suggestions that produce composite insulator with new process and design insulator with double strings and grading ring were given to prevent core rod from brittle fracture and interphase short circuit.