Improvement of suspension insulator reliability by porcelain proof testing

Modern overhead lines, particularly at EHV levels require suspension insulators of extremely high reliability. One of the most important properties required for suspension insulators is mechanical strength under tension. However, both the conventional M&E (Mechanical & Electrical) test (USASI 29.2 9.4.5)¹⁾ and the routine proof test (9.5.2) cannot give adequate assurance that each individual unit will satisfy the M&E rating and have a sufficient safety margin against the maximum working load. A new factory test, “hydraulic internal pressure test,” has been introduced to improve the strength reliability of suspension insulators.