The Bamboo 132/66 kV Interbus Transformer (IBTF) Interface consists of three (3) identical power transformers connected as shown in the SLD below; Figure Qu. 2 The nameplate obtained from one of these Figure 4 in the appendix. Routine maintenance tests have indicated that one of the existing IBTFs is nearing the end of its useful life, and it therefore needs to be replaced. Projected increases in demand supplied from this IBTF interface has also warranted a capacity upgrade and therefore the Utility has taken the decision to procure two new 180/200 MVA units to augment this interface. The final arrangement of the interface will therefore consist of two (2) of the existing transformers, and two (2) new larger capacity units, all connected in parallel. ii. Assuming that these dissimilar transformers can be paralleled, there is no power loss across each transformer, and that a total of 600 MVA of power has to be supplied from the interface when all four units are in service; iii. i. Draw the SLD representative of the proposed system with four (4) IBTFs, indicating equipment names, bus voltages, transformer voltage ratio, transformer capacities, and transformer vector group. (2 marks) Determine the positive sequence X/R ratio for the existing transformers Specify the per unit, positive sequence impedance of each of the new transformers required to ensure that for 600 MVA delivered from the interface, none of the four (4) units will be overloaded, but rather all four units will be fully loaded (100%). You are to assume that all four transformers will adhere to the IEC 60076-1/2000 standard, and that this standard specifically defines the per unit impedance of the transformers on the ONAN MVA base. Your per unit positive sequence impedance must therefore be expressed on the ONAN MVA base. (8 marks) Appendix TOSHIBA TOSHIBA DO BRASIL S.A. DIVISO DE TRANSFORMADORES FBRICA: RODOVIA FERNO DIAS (BR-381) Km 1,5 CIDADE INDUSTRIAL DE CONTAGEM - M.G. 70000/100000 FREQUENCY RATING POWER PHASES 3 TYPE TYPE OF COOLING SHORT-CIRCUIT IMPEDANCE AT 75C, VOLTAGE (V) 138600 137000 135300 133700 132000 130400 128700 127100 125400 123800 122100 120500 118800 117200 115500 113900 112200 RESISTANCE AT 75C, ZERO-SEQUENCE IMPEDANCE AT, INSULATION LEVEL WITHSTAND VOLTAGE SEPARATE SOURCE A.C/INDUCED VOLTAGE (rms kV) LIGHTNING IMPULSE (CREST KV) CHOPPED WAVE (CREST KV) ZO CT-5 151 -152 +5S1 -5S2 +951 HC/OPTLR-D ONAN/ONAF TERMINALS -9S2 HIGH VOLTAGE N A CURRENT (A) 100000 (KVA) 417 421 427 432 437 443 70000 (KVA) 292 295 299 302 306 310 314 318 5 322 326 331 335 340 345 350 355 360 O +251 252 6S1 -6S2 +10S1 10S2 +1351 -1352 16S1 KVA 60 Hz 1652 CT 1,5 2,3,4,6,7,8 9 10,11,12 13,14,15,16,17,18 19,22 20 21 26 23,24,25,27,28,29 30 449 454 460 466 473 479 486 493 500 507 515 B 351 352 751 -752 +11S1 1152 +1451 INSTRUCTIONS BOOK TOTAL WEIGHT WEIGHT OF CORE AND COIL WEIGHT OF TANK AND FITTINGS 14S2 +1751 1751 11111111 9A 98 B ON-LOAD TAP-CHANGER POS. CONNECTION 1 2 3 4 5 6 7 9C 10 70000 11 12 13 14 15 16 17 70000 70000 TNR: TOSHIBA NON LINEAR RESISTOR TERMINALS $1-52 $1-52 51-52 STANDARD IEC 60076-1/2000 SERIAL NUMBER O6063 51-52 51-52 51-52 51-52 51-52 31-52 C $1-92 51-52 KVA KVA KVA M-1 M-2 M-3 M-4 M-5 M-6 M-7 M-8 M-9 M-K M-1 M-2 M-3 M-4 M-5 M-6 M-7 M-8 M-9 BAM 66 kV BAM 132 kV 451 452 +851 952 1251 1252 1591 -1582 +1851 -1852 0 0 + BASE TAPPING, BASE TAPPING, BASE TAPPING, HV 275 650 715 500 500 TEMPERATURE RISE +1991 1992 +2251 -2252 +2651 POWER TRANSFORMER -26S2 1A IA TA 14 CURRENT TRANSFORMER RATIO MAXIMUM SHORT-CIRCUIT CURRENT (A) SYMMETRICAL (2s) ASYMMETRICAL 500 500 500 14 BAB 1000 TA SA 879 875 1.64 TA M JA 1000 1000 1500 TI-2791 120000 kg kg 58300 30200 kg CT-20 identical IBTFs is shown in DO VOLTAGE (V) 66000 a +20S1 -20S2 +2351 Page Limit- 3 pages (single sided) 2352 +27S1 2 5 -27S2 HV-N 275 650 138600/66000 V 132000/66000 V 112200/66000 V 132000/66000 V 132000/66000 V TERMINALS b A +21S1 21S2 +24S1 2452 +28S1 28S2 TANK, RADIATORS AND CONSERVATOR WITHSTAND FULL VACUUM MADE IN BRAZIL Figure 4: Transformer Nameplate 5 6 YEAR OF MANUFACTURE OIL TYPE WINDING OIL LV 140 350 385 LOW VOLTAGE 10VA B n 70000KVA 612 +25S1 25S2 +29S1 2952 10VA N C a a CURRENT N O HV 2630 7210 O n b VECTOR GROUP YN,yn0,(d1) b A O O 0 (A) C B O APLICATION PROTECTION PROTECTION PROTECTION 100000KVA 875 PROTECTION PROTECTION PROTECTION LV-N 140 350 C |||||| ACCURACY 0.05X300R3 0.05X300R3 10P20 10VA CL 0.5 / 10P20 0.1X800R2 0.05X300R3 1.0-15VA 1.0-2.5VA 10P20 0.05X300R3 10P20 10VA OIL VOLUME WEIGHT OF OIL THERMAL TIME CONSTANT (ONAF) PURCHASE ORDER NAPHTHENIC 65 60 10.9 10.5 10.2 0.2 10.8 22-0230740 LV 5260 14415 LINE DROP COMPENSATOR THERMAL IMAGE A O O b C C O +30S1 -3052 METERING/PROTECTION (DUAL PURPOSE) CHESIVA PROTECTION PROTECTION 870-00032816 (4 marks) 35000 31500 kg 1200 h Page 4 of 7 C C d d N % %