Combination Of Insulation Materials Research Articles

Alternative designs of evacuated receiver for parabolic trough collector

The paper discusses alternative designs of receivers for parabolic trough collectors with smaller rim angles. The Half Insulation Filled Receiver (HIFR) and Linear Cavity Receiver (LCR) designs have been studied and optimized for minimum heat loss. Different combinations of insulations and annulus gasses have been evaluated. From this study, the best combination of insulation material and annulus gas and its pressure has been obtained for geometry optimization of the receiver. Configuration of SCHOTT PTR 70 receiver has been considered as the base case for this study. Heat losses from the HIFR and LCR for the microtherm – air (at 0.1 atm pressure) combination are the least being 255 W/m and 246 W/m respectively. The radius ratio (RR = DG/DP) value of HIFR for this is 2.5 and insulation thickness for LCR receiver is 20 mm. HIFR and LCR show maximum optical efficiency at rim angle ψ = 45° whereas, for a conventional cylindrical receiver the same is true at rim angle ψ = 90°. Therefore, both the proposed receiver designs are expected to be suitable alternatives of evacuated receivers for parabolic trough collectors with smaller rim angle (around 45°).

Stator winding failures: contamination, surface discharge, tracking

Stator winding failures are generally attributed to groundwall or turn insulation failures. The failure mechanism involves the gradual development of a weakness in the insulation. This weakness is usually caused by a trapped void that is continuously enlarging due to ever-increasing corona or partial discharge activity. The failure mode is from the inside out. Recent studies of failures in actual machines, and of coils on voltage endurance testing, indicate that failures can occur from the outside inward. Surface contamination leads to intense surface discharge and tracking. This surface discharge can lead to rapid winding failure following the inward motion of the corona activity. This paper looks at tracking as one failure mechanism and describes a series of tests on standard insulation materials aimed at comparing the antitracking capability of the materials. The tests show that combinations of insulation materials can reduce the antitracking capacity of a rather robust insulation system and predispose it to failure.