A Study on the Reliability of Polyester Insulators Blended with Borax
Tracking is the main factor which limits the safe working electric stress of insulation in power system applications. Polymer samples have been tested in laboratory conditions according to ASTM D2303 on accelerated inclined plane tracking test. In this paper, a model based on improved Weibull statistics is proposed for estimating the breakdown time of polymeric insulating materials with borax. The confidence intervals of the Weibull shape parameter and the Weibull scale parameter are determined for the borax concentration values using the Weibull 7++ program.
The effect of colemanite on dielectric properties of polymers
The aim of this study is to investigate the effect of colemanite on dielectric properties of polymers. In this study polyester is used as the base polymer insulator. The electrical conductivity, relative permittivity and dissipation factor (tan¿) of polymers are measured as a function of colemanite concentration in polyester samples. After dielectric measurements are completed, breakdown strengths are evaluated for each concentration. Experimental measurements show that adding colemanite to polyester has an influence for good in samples which is going to be used in electrical applications.
Synthesis and properties of phosphorus-containing PEN and PBN copolyesters
Abstract Copolyesters ( V a − V d and VI a - VI d ) derived from 2-(6-oxido-6 H -dibenz〈c,e>〈l,2>oxaphosphorin-6-yl)-1,4-bis(2-hydroxyethoxy) phenylene ( II ) and bis(2-hydroxyethyl) naphthalate ( III ) or bis(4-hydroxybutyl) naphthalate ( IV ) were synthesized and characterized. Copolyesters V a - V d , VI a - VI d had been characterized by inherent viscosity, solubilities, t.g.a., d.s.c., X-ray diffraction, 1 H n.m.r., 31 P n.m.r., UL-94 and d.m.a. D.s.c. and X-ray diffraction show that the VI series of copolyesters were crystalline polymers and the crystallinity decreased with the increase in II content, whereas the V series copolyesters were amorphous polymers. The inherent viscosity of these copolyesters ranged from 0.53 to 0.68 dl g −1 . The T g values of the V series copolyesters ranged from 118 to 126°C and those of the VI series copolyesters were in the range 68–77°C; these were higher than the T g values of polyethylene naphthalate (PEN, T g : 116°C) and polybutylene naphthalate (PBN, T g : 67°C). The T d values (10%) for the V series of copolyesters in nitrogen ranged from 450 to 470°C and those for the VI series copolyesters were in the range 410–415°C; these values were also higher than that of PEN ( T d : 449°C) and PBN ( T d : 410°C). UL-94 V-0 grade could be achieved with a phosphorus content as low as 0.48 wt% for the V series and 0.97 wt% for the VI series copolyesters. T.g.a. kinetics also indicated that the V and VI series copolyesters had higher activation energies of degradation than did PEN and PBN. When these copolyphosphates were treated with fire for 10 s, intumescence is observed on the surface of copolyphosphates which retards further flaming of the polymers. DMA showed that all copolyphosphate esters have good mechanical properties ( G ′: 10 8 −10 9 Pa) before glass transition temperatures.