standards / manuals / guidelines for small hydro development - AHEC

(b)(c)there is a minimum contact of the transformer core and windings with the atmospheric air.Similarly drain oil from cooling circuit and radiators and fill dry clean oil.Whenever transformer windings are to be taken out due to any reason such as to repair adamage, thorough washing due to sludge formation or for thorough inspection to locate afault as a result of DGA or some other tests, after carrying out the necessary work for whichthe transformer was opened, do the following also:(i) Tighten all coil clamping screws to remove looseness from the windings, if any.(ii) Tighten all nuts and bolts whether metallic or made of insulating material onmechanical and electrical joints.(iii) Tighten core yoke bolts, core-clamping screws etc.Under the normal operating condition transformer has an useful life of about 25-30 years.This may vary considerably depending upon the overloads it has carried and the temperatureat which it has worked during its span of operation. Therefore for any future planning it maybe worth while to know well in advance the remanent life of the transformer in service. Thiscan be done by assessing extent of degradation of cellulosic paper through furan content intransformer oil or / and degree of polymerization (DP) of paper. It is proposed to carry outthis study after a period of 20 years of service. After knowing the remanent life in atransformer, the action can be planned in conjunction with life assessment studies ongenerating unit.As these are comparatively new studies, the data are still being built and one should go by there-commendation of the Test Laboratory. However the following figures may serve asguidelines.Degree ofFuran contentPolymerizationppm (mg/kg)New transformer 800-950 NegligibleNearing end of life 150-200 10AHEC/MNRE/SHP Standards/ E&M Works – Guidelines for Operation and Maintenance of Small Hydropower Station 51