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 mechanicalstress occurs. Knowledge of these capabilites enables future-oriented development of insulation systems for dynamically-operated long rotating machines.

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Due to the increased utilization of electric converters feeding rotating high voltage motors, their insulation is subject to transient impulse and high frequency oscillating voltages. In corresponding life time experiments with repetitive oscillating impulse voltage at winding insulation samples, higher life time coefficients were observed than known from previous investigations and operational experience. In order to understand the discharge and aging phenomena, the purpose of this work is the secure detection of partial discharges in solid and solid–air insulation types for transient impulse voltage stress by applying an adequate partial discharge (PD) measurement technique to future life time experiments. It is shown that partial discharges under impulsive voltages can be detected with conventional measuring equipment using broadband shunts, as well as inductive antennas. It becomes apparent that a precise voltage source, a precise shunt, as well as a high resolution oscilloscope are mandatory for reliable current measurement results. As a part of the analysis of the measurement data, it is shown that partial discharges can be distinguished from the displacement current caused by impulse voltages in a capacitive insulation material, as well as noise and disturbance from the measurement environment. As a first approach, a high order bandpass filter is applied in order to gain sound signals for future automated signal separation.