standards / manuals / guidelines for small hydro development - AHEC

TRANSFORMER RATING AND CHARACTERSTICSAnnexure-3.4The rating and electrical characteristics of the transformers shall be as under:S.No. Particulars 10/12.5 MVA (Outdoor type)1. Continuous kVA ratings 10/12.5 MVA ONAN/ONAF2. Type Oil immersd3. Frequency 50 C/s4. Type of cooling ONAF5. No. of phases Three6. Rating voltage on H.V. side 72.5 kV r.m.s.7. Rated voltage on L.V. side 11 kV r.m.s.8. Vector symbol YND 119. Connectionsa) H.V. Windingb) L.V. windingStar with neutral earthedDelta10. Off load taps on H.V. side (for H.V. + 2.5 to –7.5 % (in steps of 2.5%)Variation)11. H.V. and L.V. bushings suitability L.V. suitable for cable box.H.V. condenser bushings with plain shedsINSULATION LEVELS1. Insulating material to be used, shall be of class”A” as specified in the latest edition of IS:123712. The dielectric strength of winding insulation and of the bushings shall conform to valuesgiven in IS: 2026/1981 part-III amended upto date except for the changes made in thisspecification.3. The following impulse test and power frequency test voltage must be offered.Rated Highest 1.2/50 Sec. One minute power frequencySystem system positive impulse withstand voltageVoltage voltage with stand voltage -------------------------------------(kV) (kV) of line end Line Neutral(kV peak) end(kV) end(KV)------------------------------------------------------------------------------------------------------11 12 95 28 -33 36 170 70 -66 72.5 325 140 38132 145 550 230 ------------------------------------------------------------------------------------------------------The provision of note under clause 5.4 IS: 2026 (Part-III) – 1981 should be kept in viewwhile offering this parameter. The star connected windings of the transformers shall havegraded insulation. All windings for system voltage lower than 66 KV shall have uniforminsulation.3-20