12 MVA step down transformer |
| 02-13 21:50:11 来源： 作者： |
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12 MVA step down transformer Inquiry (采购产品): 12 MVA step down transformer Technical Specification for 12 MVA Transformer S No. Description Quantity 1. Three phase oil immersed 01 no. Step down Transformer The purpose will be the I/P for another step down transformer which will drive a 12 pulse converter and 6 pulse converter DC Drive motor combination for steel plant. ? Primary voltage 13.8 kv ? Secondary voltage 3.3 kv ? Rated frequency 60 Hz ? Type of cooling forced air ? No load losses 10 kw ? Load losses 75 kw ? Control voltage 110 volts ? Tap changer off load manual ? Flux density less than 1.7 tesla ? Installation outdoor 1. General conditions Elevation coastal area Temperature 50 deg centigrade maximum 15 deg centigrade minimum Humidity 96 % maximum The transformer will be oil immersed type and should comply with the power transformer specifications. All the equipments should comply with the Saudi electricity supply, or the latest standard and codes. The transformers will be kept in outdoor and humid climate. The rating of transformers will be done at ambient temp. Unless specified. In the design dusty atmosphere should be considered. All safeties should be given priority, considering the access to the equipment for maintenance and routine checkups. The control circuit voltage shall be of 110 volts dc supply, for all auxiliary relays, contactor starters and indications. The design should be so as to simplify the access to the equipment for inspection, testing, maintenance, clearing and general repairs at site. 2. Design features. Each transformer shall be suitable for operating at the full rated power on all tappings without exceeding the following temp rise. Windings 55 degrees centigrade Oil 50 degree centigrade The transformer design should be such that it should withstand the thermal and mechanical effects of any short circuits between phases and the earth at the windings when full voltage is applied across the other windings. The core, structure and tank design, shall be such that The operation shall be with minimum noise and vibrations, and no damage should be in transit or shipments. The contacts shall be design for carrying the rated current without any excessive heating, and minimum losses. The mechanism should be of brass, stainless steel to eliminate rusting, sticking or corrosion. 3. Core The frame work and the structure shall be robust enough to withstand the shocks during transport installation or operation. The core shall be clamped and care shall be taken that the clamping pressure is uniform throughout the core to avoid noise and vibrations. The frame and core bolts shall be insulated to avoid eddy current losses. The magnetic circuit shall be built of high quality low loss, non ageing, cold rolled, grain oriented, silicon steel laminations having excellent magnetic properties and suitable core material. All laminations shall be insulated from each other with rust inhibiting properties, and should withstand the pressure, mechanical vibrations and heat. Laminations shall be of CRGO silicon steel sheets annealed in non oxidizing atmosphere. To relieve the stress and retain the magnetic properties, the insulation should withstand temp of the annealing. The core and framework shall be clamped to avoid any damage during transit. The flux density should not exceed the maximum limit for over voltage and frequency. Transformers shall be designed to withstand 110 % for over fluxing regarding the rated voltage. Core should be electrically connected for effective earthing. 4. The windings The coil used for transformer windings shall be made of paper insulated continuous and smooth electrolytic copper conductors of high conductivity and 99.9% purity, and joints brazed and welded for smooth finish. The insulating material shall be of class A. all insulation shall be as per standards. The inter turn and inter coil insulation shall be designed to bear the dielectric stress. The windings shall be as ? Shall be subjected to shrinkage treatment. ? The core and the windings should be vacuum dried and impregnated immediately. ? Should be braced to avoid shocks and forces due to short circuit and switching. ? The joints which are always charged should be brazed. ? The coils should be supported using dried and high pressure compressed wedge type insulation spacers. ? The insulating material shall be compatible with transformer liquid under all service conditions. ? All the leads shall be rigidly supported. 5. Tank The tank must be made of thick gauge plates stiffened and reinforced to withstand all stresses applied during transit and short circuit. The joints and weld must be oil tight. The transformer along with the radiators and joints must be able to withstand twice the normal pressure for minimum one hour. All plates must be corrosion resistant. Cover should be provided for access to the tap changer and the bushing for maintenance and inspection. 6. Tap changer. Tap changer is required on both transformers and should be on the HT side and at exactly same instant for all the phases. The tapping’s shall be designed for repeated operations and must withstand the short circuit forces. The tap changer must be external and hand operated for offline tap changing. It should withstand 150% of the rated current. It must not occupy any intermediate position. There should be some locking arrangement for the tap. The tap position should be indicated. 7. Cooling The cooling system must be forced air cooled with fans attached with the radiators. The radiators must be detachable type and mounted with flanges nut bolts and gaskets. ? Shut off valve must be provided for each radiator at top and bottom. ? Drain plug at the bottom ? Oil Filling and air release plug at the top. ? Lifting lugs ? Thermometers pockets with thermometers in inlet and outlet pipes ? The valves must be sliced type with hand lever indicating the open & closed position. These must be of gun metal provided with blanking plates. 8. Marshalling box and terminals. The box must be weather and dust proof and should accommodate the auxiliary devices like temp. Indicator, tap changer, relays etc..The box must be mounted on the transformer with light. The box must have hinged door with front panel opening, and all parts accessible. The control cable must be heavy duty single core copper cable 2.5mm2. the external connections also be the same no joint or tapping on any cable. All terminations must be properly ferruled and indicative for easy checking, and with cable glands wherever required. The termination block must be screw type with 10 % spares. Terminal orientation should be such that there are proper gaps between each phase and conductors. The terminals for high voltages should be designed to carry full rated transformer current continuously without getting overheated and should withstand all stress and short circuit forces. The bushing insulators must be of single piece glazed porcelain having high mechanical strength, insulation, and puncture strength. The termination must be independent of the atmospheric conditions such as dust, fumes, humidity, and extreme temp. The porcelain should not be in direct contact with the hard metal. The fixing between the two joints must be with proper sealant. The cable box or duct must be of detachable type for easy disconnection. The bushings must confirm with British or Indian standards and all clamps and fittings must be hot dip galvanized. There must be bush for neutral point also. All metallic parts must be maintained at fixed potential by earthing except the core. There must be two terminals for earthing with one end of CTs earthed. 9. Accessories ? Liquid type oil temp. indicator ? Buchholz relay with alarm and trip contacts ? Winding temp. indicator with alarm and trip contact ? The radiators must be of detachable type with top & bottom shut off valve air release hole with plug, oil drain hole. ? Dehydrating breather with oil seal and silica gel in a transparent chamber ? Conservator system The transformer and the accessories should be protected against corrosion and should be painted with standard paint. 10. Inspection The |
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