15 of 124  Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 08: Electrical Works  8.5.3 Transformers  All power circuit breakers shall be fitted with an operator handle enabling manual switching. All cables shall be connected through terminals. Terminals shall be suitable for the dimension of the cables and  conductor material used.  All available signals shall be provided for SCADA and wired to the PLC for remote control and monitoring.  Transformer inlet will be confirmed from Local Electricity Supplier.  Transformer will be dry type or oil immersed type, will have MV and LV copper/aluminum winding, minimum  5 stage on load automatic tap changer, forced fan, and will have heat control probe. All material used for manufacturing transformers, will be chosen as appropriate for its use and purpose in  structure, first class quality, robust, and will have excellent physical and electrical features.  Design and manufacturing of transformers, will be accomplished by the latest technical applications and with  the best workmanship and safety factors will be taken into consideration thoroughly for the whole job. The power transformers shall be three-phase transformers with voltage level 36/0,4 kV (this value shall be  approved by Local electricity authorities) suitable rated for continuous load of the treatment plant under worst  climatic site conditions. The capacity is divided into two transformers including 1 spare in same capacity . The  Contractor has to specify the capacity based on the detailed design.  The capacity will be calculated as demand power and divided in two transformers. There will be two  transformers with equal power where both will be operated in parallel. Third one having same capacity will be  kept in spare. Spare one will be able to be put into operation when one of both is in failure. The design and specifications shall be approved by local electricity authorities. Transformer losses (no-load and  load losses) shall be designed to a minimum. The transformer rating under standard conditions shall be in  accordance with IEC-60076.  There will be plug in connection type on the transformer MV bushings.  The three phase transformer windings shall be connected in a delta-star formation with group 4 phase  displacement, high voltage to low voltage vector group reference Dyn 11. The star point of the low voltage  winding shall be brought out through the tank and suitably terminated for solid earthing.  Winding insulation shall be to Class 'A'. The temperature rise shall be limited to the maximum operating  temperature for Class 'A' materials as defined in IEC 60076 de-rated for the climatic conditions.  The high voltage windings shall be provided with tapping from +5% to -5% in 2½% stages with constant flux  voltage variation as defined in IEC 60076.  On load tap changer shall be preffered. Tap selection shall be by means of a five position (or more depend on  the area to be applied) externally operated automatic control on load tapping switch. Last decision should be  taken with the Engineer as well as Local Electrical Company.  The winding design and construction shall provide adequately designed and located coolant flow ducts so that  possible hot spots are eliminated. Windings shall be braced to withstand dynamic stresses due to short circuit  conditions. Full details shall be provided of the arrangements for taking up or eliminating coil shrinkage during  service. The core and winding shall be designed so that the loss is minimum but the ratio of copper loss to iron  loss shall be in accordance with an economic design and the manufacturer shall state the ratio used.  The complete transformer arranged for service shall be capable of withstanding an impulse voltage on the  primary windings in accordance with IEC 60076-3  8_Vol3_d4 3_Section 8 electrical works_en_GIR rev6.doc 