Dielectrics, electronic aging

Sanche, L. 1993. Electronic aging and related electron interactions in thin-film dielectrics. IEEE Trans Electr Insul 28 789-819. 

Sanche, L. 1997. Nanoscopic aspects of electronic aging in dielectrics. IEEE Trans Dielectr Electr Insul 4 507-543. 

The aforementioned reviews and assessments were assimilated to characterize the effect of dielectric, rotational, and mechanical hazards on motor performance and operational readiness. Functional indicators were identified that can be monitored to assess motor component deterioration caused by aging or other accidental stressors. The study also includes a preliminary discussion of current standards and guides, maintenance programs, and research activities pertaining to nuclear power plant safety-related electric motors. Included are motor manufacturer recommendations, responses from repair facilities to a questionnaire, in-service inspection data, expert knowledge, USNRC-IE audit reports, and standards and guides published by the Institute of Electrical and Electronics Engineers (IEEE). 

In the low-dielectric media, however, the solvation energy is mainly due to electronic polarization the standard nonpolarizable MD wiU produce in this case a negligible contribution AG . Equation 4.7 predicts in this case AG " = AGe , as expected. Equation 4.7 therefore can be considered as interpolation between... 

Silicone laminates are useful from cryogenic temperatures to about 260°C. The dielectric properties of silicones are particularly useful. Both dissipation factor and dielectric constant are low at room temperature and remain relatively constant up to 150°C. Because of the presence of the silicon atom, silicone laminates have good arc- and track resistance. The physical properties of silicones are not greatly influenced by aging, but compared with laminates that are based on other resins, the flexural and tensile strengths of silicones are not unusually high. Silicone laminates are used in electronics, heaters, rocket components, slot wedges, ablation shields, coil forms, and terminal board. 

In electronics transmission and distribution at medium and high voltage, automotive, medical and many other applications silicone rubber is a preferred material for various reasons its outstanding chemical resistance, heat ageing, dielectric (insulating) properties, unlimited pigmentability, flexibility in the cold and a wide spectrum of further advantageous properties make it the ideal material. In many cases, there is no alternative to silicone rubber. 

TSL is observable in most dielectrics in polymers the sample is commonly irradiated at liquid nitrogen temperature and heated to room temperature at a rate of approximately 3" C/min. TSL emission in many commercial polymers is negligible above room temperature and the information, which can be extracted from a single TSL measurement on the molecular environment of the trapped electrons, is not as precise as from ESR. The TSL spectrum of a polymer may contain both fluorescent and phosphorescent components. TSL provides information about ageing processes and can be used as a method for early recognition of damage in polymers. Fleming [488] has reviewed thermally stimulated luminescence (TSL) for the analysis of polymers. 

FIG. 33 Dependencies of electrical properties dielectric constant (a) and dissipation factor (b) on irradiation aging measured at various frequencies (accelerated electrons dose 10 MGy dose rate 3 kGy/h). (Adapted from Ref. 67.) Column 1 1 kHz, nonirradiated materials column 2 1 kHz, irradiated materials column 3 1 MHz, nonirradiated materials column 4 1 MHz, irradiated materials. 

In addition to PALS, other spectroscopic techniques that have heen used to investigate physical aging are electron spin resonance spectroscopy (ESR) [83], fluorescence spectroscopy [84—86], dielectric spectroscopy [87], and Fourier-transform infrared spectroscopy (FTIR) [88]. 

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