Power Research

K. Karunakara ¹, P. N. Ashitha ², S. Ganga ³

Affiliations
1 Joint Director, Heat Run Test Laboratory, Insulation Division, Central Power Research Institute, Bangalore - 560 080, IN
2 Engineering Officer, Insulation Laboratory, Central Power Research Institute, Bangalore - 560 080, IN
3 Additional Director, Insulation Division, Central Power Research Institute, Bangalore - 560 080, IN

Abstract

Commonly used grades for transformer core stampings are Cold Rolled Grain Oriented Steel of grades M3, M4, M5 and M6. As the flux density increases, the magnitude of no load loss and no load current increases. But studies also indicated that, a given magnitude of core loss can be attained with both high and low magnitudes of no load current. This result can be used to ascertain the presence of inferior grade core material. It is essential to operate the transformer in the linear region of BH curve. Operation in saturated state will result in increased no load current which in turn will have a detrimental effect on the temperature rise of transformer as additional I2R losses are generated. With the limits of temperature rise being more stringent in IS standard than in IEC, the choice of flux density is crucial. In this paper an attempt is made to realize the best operational flux density, which gives a benchmark for deciding the magnitude of no load current and the corresponding no load power factor.

Keywords

No load losses, copper losses, temperature rise, CRGO

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Moumita Naskar ¹, P. N. Ashitha ¹, K. G. Rakesh ¹

Affiliations
1 Insulation Division, Central Power Research Institute, Bangalore – 560080, Karnataka, IN

Abstract

Underground Polyvinylchloride (PVC) sheath power cables are exposed to the atmospheric condition during installation. Depending on the atmospheric conditions the cable sheath is facing extreme environmental stresses such as ambient temperature (high and low), direct sunlight (UV) radiation, rain or water accumulation etc. The life of PVC cables is reduced by being exposed to harsh environmental conditions and can subsequently damage the unprotected cables. This work is aimed to the study of the effects of UV radiation and low temperature on PVC cable outer sheaths. Three commercially available PVC cable were chosen for the study. UV exposed PVC insulations become brittle after UV exposure and in low temperature. UV exposure eventually results in material degradation, diminishing the performance characteristics of the material. Thermogravimetric Analysis (TGA) was used to characterize the thermal behavior of PVC cable insulation materials before and after UV ageing. In addition, Fourier-transform infrared spectroscopy (FTIR) was used to reveal the chemical processes that caused the UV degradation of the sample. A good agreement between results of the methods was found. Exposure to low temperature resulted in a reduction in stiffness of the polymeric structure caused embrittlement which transformed the PVC structure from a flexible material capable of undergoing large strain elastic behaviour to a stiffer material with higher yield behaviour.

Keywords

Cold Elongation, UV Radiation, FTIR, PVC, TGA

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