Comparison of Methods to Detect Thermomechanical Ageing of the Insulation System for Rotating High-Voltage Machines

Abstract

Increased dynamic operation of long rotating high-voltage machines as well as elevated operating temperatures lead to intensified thermomechanical stress in the insulation system of global vacuum-pressureimpregnated machines. Meanwhile, the requirements regarding reliability of the machine and the electric insulation system remain high. Consequences of thermomechanical stress include delaminations and abrasion. To satisfy the high standards of longevity, reliable diagnosis of thermomechanical ageing is essential to allow manufacturers to develop and improve countermeasures. This work identifies diagnostic tools, which investigate the effects of thermomechanical ageing on model replicates of machine insulation systems. The longitudinal thermal expansion of the conductor during dynamic operation is replicated by applying mechanical force to the conductor of specimens, thus inducing mechanical stress in the insulation system. Recurring measurements of partial discharges, dielectric losses and capacitance are evaluated regarding their sensitivity in detecting resulting ageing phenomena. The study reveals that partial discharge measurements detect preliminary damages before insulation rupture caused by mechanical
stress occurs. Knowledge of these capabilites enables future-oriented development of insulation systems for dynamically-operated long rotating machines.