A thermal cycling type test for generator stator winding insulation

Stone, G.C.; Lyles, J.F.; Braun, J.M.; Kaul, Claudia

doi:10.1109/60.103645

Cited by 44 publications

(8 citation statements)

References 3 publications

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“…influences the potential insulation life L. Loss factor and partial discharge measurements during thermal cycling tests [8,14,16,17] on high voltage winding insulations confirm the formation of delaminations between the strand and the groundwall insulation ( Figure 1) which is also observed in rotating machinery [1,7]. However, there are insulation systems for which both breakdown voltages and voltage endurance are not reduced even after several hundred temperature cycles.…”

Section: Introductionmentioning

confidence: 91%

Retardation of electrical tree propagation by resin degradation

Weiers¹,

Keller²,

Hutter

et al. 2006

Int Trans Elec Energy Syst

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SUMMARYIn order to improve insight into the effect of delaminations between the conductor and the groundwall insulation on the ageing of high voltage rotating machinery insulation, the influence of the polymer degradation on tree growth has been studied. Simultaneous partial discharge measurements and photograhic observations have been conducted in order to investigate the effect of the degradation of the resin on electrical tree propagation. The photographic observation indicates that the degradation of the resin retards the tree propagation after the tree having failed to penetrate a mica barrier. As the resin is degraded and in part rendered conducting, the partial discharges change both in magnitude and in terms of phase resolved partial discharge patterns. These partial discharge measurements are promising to improve insight into the processes involved in winding insulation ageing, when photographic observations are unattainable. Moreover the differences found between various resins offer an explanation why various types of winding insulation have been found to differ in their capability to withstand thermal cyclic ageing.

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Section: Introductionmentioning

confidence: 91%

Retardation of electrical tree propagation by resin degradation

Weiers¹,

Keller²,

Hutter

et al. 2006

Int Trans Elec Energy Syst

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“…By that time, such components had accumulated an estimated number of start-stops superior to 10,000 (ten thousand). The relevance of having components from a Pumped-Storage unit in the study resides in the fact that the series of start-stops is normally assumed as source of one of the most relevant stressors concerning aging of HV insulation on large long-core units [2]. The insulation technology used in such bars is based upon the epoxy-mica system, whose thickness was designed for this 20 kV-rated unit to produce maximum electrical stresses under operation below 3 kV/mm.…”

Section: A Air-cooled Pumped-storage Operating Regime -Type Amentioning

confidence: 99%

Evaluation of Roebel bars aged under service conditions in large hydrogenerators

Silva

Pereira

Lamas

et al. 2015

2015 IEEE Electrical Insulation Conference (EIC)

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The evaluation of high-voltage groundwall insulation aged under long-term operating conditions is addressed using three sets of Roebel bars removed from large hydrogenerators after several decades of service. To cover an important cross-section of the possible operating regimes for typical hydros, the units involved in the study were selected to represent (i) the air-cooled Pumped-storage, (ii) the air-cooled base-load and (iii) the water-cooled base-load service regimes. Experimental techniques were used to permit assessment of the insulation condition under visual, electrical and morphological aspects. Contrary to what is usually assumed, the results suggest that the pumped-storage operating regime, with its repeated thermal-mechanical cycles of start-stops may create only minimum aging to the groundwall insulation while, in some particular cases, units operating at relatively low temperatures and under mild base-load conditions, may be found to exhibit a more severe insulation degradation in the long run.

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“…Ontario Hydro has developed a similar aging test in order to select winding designs which have superior resistance to thermal cycling [4]. The test is done on several full-size stator bars simultaneously.…”

Section: Generators These Units Tend To Operate At Highmentioning

confidence: 99%

Quality assurance testing for large air-cooled generator stator winding insulation

Braun

Gupta

Sedding

Proceedings:Electrical Electronics Insulation Conference and Electrical Manufacturing &Amp; Coil Winding Conference

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There is a growing trend to specify and use smaller generating unit sizes than was prevalent before. Furthermore, this new equipment is often operated at the limits of the design in order to maximize performance. In response to these pressures, utilities and independent power producers, are specifying large air-cooled generators with capacities of up to 300 MVA. Due to advances in materials and design, and consequently lower costs, these units compete effectively with hydrogencooled machines at these ratings.From a user perspective, there remain concerns which need to be addressed.Within this contribution, attention is focused on outstanding issues related to the problem of testing the stator windings of such machines.The paper will discuss those areas of concern which are considered critical to the long term reliability of the stator windings of large air-cooled machines. In addition, efforts currently underway to address some of the issues thus identified will be described.

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A thermal cycling type test for generator stator winding insulation

Cited by 44 publications

References 3 publications

Retardation of electrical tree propagation by resin degradation

Retardation of electrical tree propagation by resin degradation

Evaluation of Roebel bars aged under service conditions in large hydrogenerators

Quality assurance testing for large air-cooled generator stator winding insulation

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