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Technical Specification for 5 Mva and 10 Mva Power Transformer

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TECHNICAL SPECIFICATION FOR 5 MVA AND 10 MVA POWER TRANSFORMER SPECIFICATION NO. APDCL/PP&D/T&C/STS/PTR/2020/1 1. SCOPE 1.1. ThisSpecificationprovidesfordesign,engineering,manufacture,assembly,stageinspection, finalinspectionandtestingbeforedispatch,packinganddeliveryatdestinationSub-stationby road transport, transit insurance, unloading at site/stores of 5 MVA and 10MVA,33/11 KV Power Transformer(s) with on load tap changer, complete with all fittings, accessories, associated equipment‘s, spares, 10% extra Transformer Oil, required for its satisfactory operation in any of the sub-stations of the purchaser 1.2. The core shall be constructed either from high grade, non-aging Cold Rolled Grain Oriented (CRGO) siliconsteellaminationsconformingtoM-4grade of BIS certified with lamination thickness not more than 0.23mm to 0.27mm or better (Quoted grade and type shall be used). The maximum flux density in any part of the cores and yoke at normal voltage and frequency shall be such that, at 12.5% overvoltage conditions it should not be more than 1.9Tesla. The supplier shall provide saturation curve of the core material, proposed to be used. Prior to inspection and testing of the transformer the supplier shall submit on request following curves of the core manufacturer: 1.2.1. i. Flux Density vs Core Loss 1.2.2. Flux Density vs Excitation. 1.3. Laminations of different grade(s) and different thickness(s) are not allowed to be used in any manner or under any circumstances. The core shall have magnate coating as insulation. The assembled core shall be securely clamped on the limbs and yoke with uniform pressure so as to minimize noise emission from it. The insulation structure for the core to bolts and core to clamp plates shall be such as to withstand a voltage of 200V at 50Hz for 1min. 1.4. The scope of supply includes the provision of type test. The equipment offered should have been successfully type tested within five years from date of tender and the designs should have been in satisfactory operation for a period not less than three years as on the date of order. Compliance shall be demonstrated by submitting, (i) authenticated copies of the type test reports and (ii) performance certificates from the users, specifically from Central Govt. /State Govt. or their undertakings. However, if it is found that the bidder has submitted type test reports but those have not been conducted on identical design of equipment/material as per APDCL specification, the same may be accepted subjected to the following condition: 1.4.1. APDCL at its discretion may request the successful bidder to conduct type test on the identical design as per APDCL specification. 1.4.2. Such type tests, if required to be carried out at CPRI/ERDA in presence of APDCL Engineer for which no extra cost shall be charged to APDCL. 2. SYSTEM CONDITIONS The equipment shall be suitable for installation in supply systems of the following characteristics. 50 Hz± 5% Frequency 33 KV Nominal system voltages 11 KV 33KV System 36.3KV Maximum system voltages 11 KV System 12 KV 33KV System 31.5KA Nominal short circuit level (Based on apparent 11 KV System 25KA power) Insulation levels : 33KV System 170KV (peak) 11 KV System 75 KV (peak) 1.2/50 μ sec impulse withstand voltage 33KV System 70KV (rms) Power frequency 1 minute withstand (wet and 11 KV System 28KV (rms) dry) voltage 11 KV System Solidly earthed Neutral earthing arrangements 3. SERVICE CONDITIONS: maximum altitude above sea level 1000m minimum ambient air temperature 45° C maximum daily average ambient air 40° C temperature minimum ambient air temperature 2° C maximum temperature attainable by an 60 ° C object exposed to the sun maximum yearly weighted average 32° C ambient temperature 2 APDCL/ BIDDING DOCUMENT / TS maximum relative humidity 100% average number of thunderstorm days 4550(MV) per annum (isokeraunic level) average number of rainy days per annum 120 average annual rainfall 2200 mm maximum annual rainfall 3500 mm maximum wind pressure 260Kg/m² Seismic Level 0.24g to 0.48g Environmentally, the region where the equipment will be installed is subject to high relative humidity, which can give rise to condensation. Outdoor material and equipment shall be designed and protected for use in exposed, heavily polluted, corrosive, tropical and humid atmosphere. ALTITUDE FACTOR If the equipment is to be installed in the hilly area, necessary correction factors as given in the Indian Standard for oil temperature rise, insulation level etc. shall be applied to the Standard Technical Parameters given above. 4. CODES & STANDARDS 4.1 The design, material, fabrication, manufacture, inspection, testing before dispatch and performance of power transformers at site shall comply with all currently applicable statutory regulations and safety codes in the locality where the equipment will be installed. The equipment shall also conform to the latest applicable standards and codes of practice. Nothing in this specification shall be construed to relieve the contractor of this responsibility. 4.2 The equipment and materials covered by this specification shall conform to the latest applicable provision of the following standards. IS:5 Colour for ready mixed paints IS:325 Three Phase Induction Motors IS:335 New insulating oil for transformers, switch gears IS:1271 Classification of insulating materials for electrical machinery and apparatus in relation to their stability in services 3 APDCL/ BIDDING DOCUMENT / TS IS:2026(Part I to IV) Power Transformer IS:2071 Method of high voltage testing IS:2099 High voltage porcelain bushings IS:2147 Degree of protection IS:2705 Current Transformers IS:3202 Code of practice for climate proofing of electrical equipment IS:3347 Dimensions for porcelain Transformer Bushings IS:3637 Gas operated relays IS:3639 Fittings and accessories for power Transformers IS:5561 Electric Power Connectors IS:6600/BS:CP‟10:0 Guide for loading of oil immersed Transformers IS:10028 Code of practice for selection, installation and maintenance of transformers, Part I. II and III C.B.I.P. Publication Manual on Transformers If the standard is not quoted for any item, it shall be presumed that the latest version of Indian Standard shall be applicable to that item. The equipment complying other internationally accepted standards, may also be considered if they ensure performance superior to the Indian Standards. 5. SPECIFIC TECHNICAL REQUIREMENTS Sl Particulars 33/11 KV Power Transformer 1 Rated MVA 5MVA & 10 MVA (ONAN rating) 2 Number of Phases Three 3 Vector group Dyn-11 4 Type of installation Outdoor 5 Frequency 50HZ ( +/- )5% 6 Cooling Medium Insulating Oil (ONAN) 7 Type of Cooling ONAN (Oil natural / Air natural) 8 MVA Rating 100% corresponding to ONAN 4 APDCL/ BIDDING DOCUMENT / TS 9 Rated Voltage :- High Voltage winding 33kV Low Voltage winding 11kV 10 Highest continuous system voltage a) Maximum system 36.3KV / 12 KV voltage ratio (HV / LV ) b) Rated voltage ratio 33KV /11 KV (HV / LV ) 11 Winding Material Electrolytic Copper 12 Winding Connection :- High Voltage Winding DELTA Low Voltage Winding STAR 13 Vector group reference Dyn11 14 No. of windings Two winding Transformers 15 Method of System Solidly grounded on LV side Earthing 16 Neutral terminal to be On LV side only brought out 17 Core Material CRGO ( M-4 / higher grade) 18 Core Assembly Boltless type 19 Type of Tap Changer On-load tap changer (OLTC) 20 Range of Tapping + 5% to – 15% in 17 equal steps of 1.25% each on HV winding 21 Intended regular cyclic As per IEC –76-1, Clause 4.2 overloading of windings The Power transformer shall be suitable for operating under overload condition as specified in IS 6600 and a separate Over Loading chart should be submitted along with offer. 22 a) Anticipated Around 10% unbalanced loading 5 APDCL/ BIDDING DOCUMENT / TS b) Anticipated continuous 110 % of rated current loading of windings (HV / LV) 23 Over Voltage operating 112.5 % of rated voltage (continuous) capability and duration 24 Withstand time for three 2 Seconds phase short circuit 25 Maximum current density 2.4Amp/ Sqmmfor copper conductor at any working for HV and LV winding tap including extreme tap 17 (-15% voltage). for rated current 26 Magnetizing Current 1% of full load current. 26 Maximum flux densityin 1.55 Tesla any part of the core and yoke at rated MVA, rated voltage i.e 33kV / 11kV and system frequency of 50 Hz 27 Maximum Flux Density in 1.9 Tesla any part of the core and yoke at 112.5 % of rated voltage i.e 33 KV /11 KV and system frequency of 50 HZ 28 Insulation 33kV 11kV a) Type of insulation Uniform Uniform b) One minute power 70kV 28kV frequency withstand Voltage(kV rms) c)1.2 / 50 microsecond 170 75 wave shape Lighting Impulse withstand voltage (KVP) 29 Nominal short circuit 31.5KA 25KA level (Basing on apparent power) 30 Insulation level of bushing a) Lightning Impulse 170 75 withstand (KVP) 6 APDCL/ BIDDING DOCUMENT / TS b) 1 Minute Power 70 28 Frequency withstand voltage (KV –rms ) 31 Minimum clearances in Phase to Phase to ground Phase to ground air (mm) Phase in Oil a) HV 400 320 40 b) LV 280 140 25 32 c) Creepage distance 972 324 (mm) (minimum) 33 Percentage impedance MVA Rating %Impedance Tolerance % voltage on normal tap and MVA base at 75o C 5 7.15 10 corresponding to HV/ LV rating and applicable 10 8.35 10 tolerances: (No negative tolerance shall be allowed) 34 Permissible Temperature Rise over ambient temperature of 40 / 45˚C a) Of top oil measured by 40˚C thermometer b) Of winding measured 45˚ C by resistance 35 Noise level at rated Transformers shall be designed with particular care voltage and frequency to suppress at least the third and fifth harmonic voltages so as to minimize interference with communication circuits.
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