Understanding polymer degradation under voltage stress in PV applications
AC Partial Discharge (PD) specification has been a key design parameter for PV backsheets, as called for in IEC 61730-1. In previous work, we have studied how the structure of polymeric materials can impact their behavior in this test. In this paper, we shift the focus to consideration of potential root causes which can lead to electrical degradation in actual usage (e.g. a PV module producing DC power), and the efficacy of the AC partial discharge test in air and oil to identify these. The suitability of utilizing AC voltage stresses in PV is also challenged in this paper. New experimental evidence is presented as to why testing partial discharge with AC with specimens immersed in the medium is not suitable for testing of solar backsheet materials. PD measurements can be very different for tests performed in air versus oil, and can lead to different pass/fail conclusions for the same material. When tested in oil, materials with voids had a much lower Ve than materials with no voids; in air, there was no difference in Ve for a material prepared with and without voids. With regard to AC versus DC testing the time to breakdown versus voltage was measured for both; these are not linearly related: the AC and DC breakdown voltages for one material study were 25 kV(AC) and 85 kV (DC), more than 3× difference; the voltages which led to breakdown after 10000 seconds were 5 kV(AC) and 50 kV (DC), a 10× difference. The issues raised in this study are active areas of discussion for the TC 82 WG2 Standards Committee.
Partial Discharge Measurements on Glass-Mica-Epoxy Samples for electrical insulation during Accelerated Thermo-Oxidative Aging
The stator windings of large air-cooled rotating machines are mainly insulated with mica-glass fabric impregnated with epoxy resin. In service, these materials are submitted to thermal, mechanical and electrical stresses. A specific aging arrangement has been set-up allowing artificial thermo-oxidative aging of samples, thanks to the application of a dry O2 pressure at a controlled temperature. Three different materials, one reference material and two candidate materials, of different thermal classes or different thermal conductivity, have been aged and compared. Partial Discharges (PD) analysis of the samples has been conducted and correlated with samples' morphology. Because of the small size of the samples, a specific PD measurement arrangement has also been set-up. After only a few hundred hours aging, delaminations of a few tens of μm were observed within the samples. PD measurements revealed a decrease of the PD Inception Voltage (PDIV) on these aged samples. The PDIV on samples with specific cavity thickness were also in good agreement with Paschen law. PD measurements, especially the PDIV, seem to be a good indicator of the progress of the aging.
Heritage Sites of Astronomy and Archaeoastronomy in the context of the UNESCO World Heritage Convention: A Thematic Study
"Following the publication of the first ICOMOS–IAU Thematic Study (“TS1”) in 2010, the IAU requested its Working Group on Astronomy and World Heritage to develop particular case studies in greater detail, so as to explore further and clarify some of the key issues highlighted in TS1 that can arise in the particular case of astronomical heritage sites. In doing so, it would further encourage and aid State Parties in the development of nominations. In collaboration with ICOMOS, nine “extended case studies” were duly prepared for discussion at a workshop held at Mount Cook, New Zealand, in June 2012 and presented at the IAU General Assembly in August of that year. 
 
A particularly complex issue is the recognition and protection of dark skies. Dark sky areas cannot in themselves be considered as potential World Heritage Sites, but a thematic chapter by Michel Cotte considers a range of ways in which dark sky values can be interrelated with broader cultural or natural values of a place and thereby contribute to its overall cultural or natural value and potential OUV. Other issues explored in TS2 include the need to balance archaeoastronomical considerations in the context of broader archaeological and cultural values; the potential for serial nominations, for example among groups of monuments whose astronomical significance is only evident from the group as a whole; and management issues such as preserving the integrity of astronomical sightlines through the landscape. 
 
The case studies included in TS2 include seven-stone antas (prehistoric dolmens) in Portugal and Spain, the thirteen towers of Chankillo in Peru, the astronomical timing of irrigation in Oman, Pic du Midi de Bigorre Observatory in France, Baikonur Cosmodrome in Kazakhstan, and Aoraki–Mackenzie International Dark Sky Reserve in New Zealand. A case study on Stonehenge, already a World Heritage Site, focuses on preserving the integrity of the solstitial sightlines." 
 
Source: UNESCO portal to the heritage of astronomy