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

Justification of choice of methods for diagnostics of insulation condition of electrical machines of electric railway stock

“…The method of high-frequency capacitance impedance is also used to monitor the deterioration of the insulation condition of electric motor coils. Periodic measurements of partial discharges, dielectric losses and capacitance, as shown in [21], are the most effective for assessing the phenomenon of insulation aging.…”

Methods of Diagnosing the Insulation of Electric Machines Windings

“…The insulating system of the windings of electrical machines is multi-layer and consists of coil and main (slot) insulation [2,[8][9][10][11]. The thickness of the insulation is selected with a margin so that its durability to breakdown is greater than the existing voltage.…”

“…However, this insulation also ages and changes its parameters. This is influenced by [3,4,[6][7][8][9]13,[16][17][18][19][20]:…”

“…Prolonged exposure to high intensity of partial discharges can lead to the deep erosion of insulating materials and the reduction of dielectric strength [4,12]. Therefore, discharge-resistant materials, such as mica and mica products, are used in the insulation systems of electrical machines [9,10,16]. The possibility of gaps in the insulation is limited by the use of an appropriate manufacturing technology.…”

“…The quantity characterizing dielectrics is the tangent of the dielectric loss angle tgδ, i.e., the ratio of the intensity of the real component (I R ) to the imaginary component (I C ) of the electric current flowing through the dielectric in an alternating electric field (Figure 6) [9].…”