El Menia Farms Substation (66/22 KV, 2X40 MVA) - Power Transformer & Accessories - PDF

# EL MENIA FARMS SUBSTATION (66/22 KV, 2X40 MVA) ## SECTION FOUR ### POWER TRANSFORMER AND ACCESSORIES #### TABLE OF CONTENTS | CLAUSE | DESCRIPTION | Page | |---|---|---| | 4.1. | GENERAL | 3 | | 4.2. | TYPE AND MAIN CHARACTERISTICS | 3 | | 4.3. | LIMITS OF TEMPERATURE RISE | 4 | | 4.4. | CONTIN...

# EL MENIA FARMS SUBSTATION (66/22 KV, 2X40 MVA) ## SECTION FOUR ### POWER TRANSFORMER AND ACCESSORIES #### TABLE OF CONTENTS | CLAUSE | DESCRIPTION | Page | |---|---|---| | 4.1. | GENERAL | 3 | | 4.2. | TYPE AND MAIN CHARACTERISTICS | 3 | | 4.3. | LIMITS OF TEMPERATURE RISE | 4 | | 4.4. | CONTINUOUS POWER RATING | 4 | | 4.5. | LIMITED PERIODS RATING | 4 | | 4.6. | ABILITY TO WITHSTAND SHORTCIRCUIT | 5 | | 4.7. | EFFICIENCY AND LOSSES | 5 | | 4.8. | HARMONICS | 7 | | 4.9. | NOISE LEVEL | 7 | | 4.10. | TRANSFORMER PARALLEL OPERATION | 8 | | 4.11. | TRANSFORMER COOLING SYSTEM | 8 | | 4.12. | TRANSFORMER CONSTRUCTION | 10 | | 4.13. | ON LOAD TAP-CHANGER | 12 | | 4.14. | OIL PRESERVATION SYSTEM | 15 | | 4.15. | BUSHINGS | 15 | | 4.16. | CURRENT TRANSFORMERS | 16 | | 4.17. | OIL FOR TRANSFORMER | 16 | | 4.18. | TRANSFORMER MONITOR AND PROTECTION | 18 | | 4.19. | TERMINAL CABIENT | 19 | | 4.20. | ACCESSORIES AND FITTINGS | 19 | | 4.21. | REMOTE CONTROL AND PROTECTION | 20 | | 4.22. | GAS PROTECTION | 20 | | 4.23. | PROTECTION AGAINST EXCESSIVE HEATING | 20 | | 4.24. | PROTECTION AGAINST HEATING OF TRANSFORMERS | 20 | | 4.25. | PROTECTION AGAINST LOW OIL LEVEL | 20 | | 4.26. | PAINTING | 21 | | 4.27. | NAMEPLATES | 21 | | 4.28. | MAINTENANCE MATERIALS | 21 | | 4.29. | DRYING OUT OF TRANSFORMER | 21 | | 4.30. | SUBMITTALS | 21 | ### 4.1. General 1. The data and conditions specified in this chapter apply to the power transformers, accessories and fire fighting system. 2. The transformers shall be three phase oil immersed type and constructed in accordance with the latest edition of [IEC] standards unless otherwise specified hereinafter. 3. The transformers shall be transported with the tank under pressure of dry nitrogen gas and provided with pressure gauge suitably protected from damage. The pressure and temperature shall be recorded at the time of the transformer leaves the factory, the recorder information shall be given so that it can be compared with pressure and temperature readings after the transformer has been received at site to ascertain if any leakage has occurred. 4. Ensure that the transformer arrives at site in an uncontaminated condition. 5. Three axis impact recorders shall be provided on different places on the transformer to record any shocks, the capacity of the battery shall be sufficient to operate the impact recorder two months continuously, method of evaluating the shocks and places of the shocks recorders on the transformer to be submitted with tender the shocks recorders shall be protected from damage. 6. The transformers shall be unloaded either in Pre-determined storage area or on their foundations. 7. The manufacturer of the transformer and its main accessories should have ISO 9001 certificate, these certificates should be submitted with tender. ### 4.2. Type and main characteristics of the transformers: 1. The transformers shall be three phases, 50 Hz, Oil immersed, ONAN/ONAF cooling type, with on load tap changer suitable for outdoor tropical conditions. All power transformers of the above specified types shall be installed outdoor. 2. Ratings and characteristics of the transformers: * Rating: 32/40 M.V.A Transformer ratio at main tap. * And full load at 0.8 P.F: 66/22 KV 3. The transformer shall be operated and loaded safely, if the breakdown of the insulating oil is 40 K.V. / 2.5 mm gap. 4. All transformers shall be equipped with on-load tap changers, fans, radiators, oil conservators (expansion tanks), etc. 5. The star connection windings, neutral-bushing insulators shall be provided. 6. The principal tapping is the tapping corresponding to 100% tapping factor. ### 4.3. Limits of temperature rise 1. The climatic conditions specified herein and the effect of operation in sunshine with high solar intensity for 12 hours per day shall be taken into consideration in the design of the transformers. 2. The transformers shall be able to deliver the rated continuous power with the tap changer set at any tapping of the primary winding, without exceeding the following temperature rise limits over ambient temperature: * Winding temperature rise (measured by resistance method): $50 °C$ * Top oil temperature rise (measured by thermometer at top level): $45 °C$ * Hot spot temperature rise (by calculation, based on the highest winding's temperature and Hotspot factor not less than 1.3): $60 °C$ 3. The winding maximum (hot spot) temperature shall not exceed $105 °C$ under normal loading conditions. The above temperature rise limits shall be based on the ambient temperature of $45° C$. 4. The temperature rise will be measured on one transformer of each type to be delivered. If the temperature rise of this transformer exceeds the guaranteed figures a fine of 1.8% of the total cost of the transformers of this type shall be imposed for every one degree higher than the guaranteed temperature rise. If the excess rise of temperature beyond than $5°C$, E.E.T.C shall reject such transformers. ### 4.4. Continuous Power Rating 1. The transformers shall be able to deliver for an unlimited period of time at any tapping of the tap changer, the following continuous power ratings without exceeding the limits of temperature rise: * ONAN Cooling: up to 80%. * ONAF Cooling: > 80%. 2. The continuous power ratings should be verified by the temperature rise test. ### 4.5. Limited Periods Rating 1. The transformer shall be capable of carrying 10% overload for two hours at any tapping, starting from steady state full load without exceeding the specified limits of temperature rise. 2. The limited periods rating should be verified by the temperature rise test by calculation is not accepted. ### 4.5.3. Tenderers shall state the duration for which the transformers can carry 10%, 25%, 50%, 75% and 100% overload at extreme minus tapping after having been loaded for an unlimited period of time with 4/4, 3/4, 1/2 and 1/4 of its maximum continuous power rating without exceeding the specified limit of temperature rise. ### 4.5.4. Tenderers should submit with the temperature rise test report the loading curves as mentioned in IEC 60076.7 Annex [E] which to be applied on the offered transformers, the curves should be for the loading capacity on the principal tapping as well as on the extreme tapping. ### 4.6. Ability To Withstand Short Circuit 1. The transformers and their accessories shall be able to withstand the thermal and dynamic effect of external short circuit of the system which is specified in sec. three. 2. The transformers and their accessories shall be able to withstand for two seconds duration the rated thermal short circuit current. 3. The transformers and their accessories shall be able to withstand dynamic short circuit current 250 m sec. ### 4.7. Efficiency And Losses 1. The transformers shall be designed for maximum efficiency and minimum losses, since this will be considered in the comparison of tenders. 2. When comparing between different tenders, the present value of the capitalized cost of losses in the transformers shall be added to the transformer price according to the following formula : * $Pw = (K \times EF \times C) \times 8760 (Wir + Wca \times aP² + bFc)$ * $=(k_{non-fuel} \times C_{non-fuel} + k_{fuel} \times C_{fuel}) \times 8760 \times(Wtr + Wcm \times aP² + bfc)$ in L.E * Where: * $Pw$ Present worth cost of losses at annual rate of interest over 30 years. * $C$ Is the Cost per kWh = 1.1 LE using the VHV tariff values that correspond to 4rd year (2019/2020) of the government's program. * $EF$ Is the escalation factor for the non-fuel component according to the cabinet approval = 5% * $K_{fuel}$ Is the present worth factor for fuel component (at 14% discount rate, 30 years) = 7.003 * $K_{non-fuel}$ Present worth factor for non-fuel component (at 14% discount rate, 30 Years, 5% EF) = 10.677 * $C_{fuel}$ Is cost of fuel component = 0.6849 LE//kWh. * $C_{non-fuel}$ 0.4151 L.E/kWh. * $Wir$ No load losses in kW at normal voltage and main tapping. * $WCu$ Load losses in kW at full load, principal tapping and reference temperature 95 °C, in case the' offered reference temperature (0 °C) is lower than 95 "C, the load losses will be multiplied by (235+95)/(235+0) * $a$ Is the LSF (load loss factor) = 0.4 * $P$ Peak load in PU = 1.1 * $b$ per unit working time of cooling fans per day = 0.4 * $Fc$ fans consumption in kW at transformer full load and specified overload, rated voltage and extreme minus tapping. * $Pw = (K \times EF \times C) \times 8760 (Wir + WCu \times aP² + bFc)$ * $=(k_{non-fuel} \times C_{non-fuel} + k_{fuel} \times C_{fuel}) \times 8760 \times(Wir + Wcu \times aP² + bfc)$ in L.E ### 4.7.2.1. Based on the a/m formula, PW shall be added to the tender price in (LE/KW), by the following rates: * 80840.5 L.E/kW of NO-Load losses. * 39126.8 L.E/kW of Load losses. * 32336.2 LE / kW of Fans consumption. ### 4.7.2.2. In case the Tr. losses (no load losses, full load cupper losses, fans consumption) during tests exceed the guaranteed values in the offer, but within the standard permissible tolerance, penalty according to the following formula : * Penalty = (K x EF x C) x 8760 x [AWir + AWcu x aP² + b AFc) in LE. * WAWir and AWcu are difference between the test and guaranteed value of iron losses at full voltage and copper losses at full load on the Tr. at main tapping. Based on the a/m formula, the penalty shall be calculated according to the following rates: * 80840.5 L.E / kW exceeds the guaranteed NO-Load losses. * 39126.8 LE / kW exceeds the guaranteed Load losses. * 32336.2 LE / kW exceeds the guaranteed Fans consumption. ### 4.7.3. The applied penalty on any transformer shall be deducted from the transformer price at shipping and with the same currency of the transformer contractual price using the free exchange market transfer selling rate on the date of shipping of such transformer. ### 4.7.4. If the excess loss values measured during factory tests exceed the allowable tolerance set in IEC standards, as well if excess in the fans consumption is higher than 15% then the owner has the right to reject such transformer. ### 4.7.5. No credit shall be given for any decrease in the values of losses below the guarantee values. ### 4.8. Harmonics: 1. The transformers shall be designed with particular attention to the suppression of harmonic voltages, especially the third and fifth, so as to eliminate wave form distortion and any possibility of high frequency disturbance by inductive effect or of circulating currents between the neutral points of different transformers reaching such a magnitude as to cause interference with telephone or communication circuits or other undesirable effects. 2. The percentage deformation, appearing in the voltage wave of one winding of a transformer, when the other winding is energized from a source of pure sine wave shall not exceed 5% (five percent) of the fundamental wave amplitude. ### 4.9. Noise Level The transformers shall be so designed and constructed that harmful vibrations are eliminated and that non-avoidable noise will occur at any operating conditions. The transformers are subject to a noise test according to IEC 60076-10. The measured values should not exceed the specified values. ### 4.10. Transformers Parallel Operation 1. The quoted transformer shall satisfy the parallel operation conditions at different tap positions to avoid the circulating current. 2. The tap changer mechanism shall automatically adjust the tap changer to maintain the secondary voltage equal on all transformers to avoid circulating currents. ### 4.11. Transformer Cooling System #### 4.11.1. General 1. Tenderers shall quote for natural oil circulation forced air cooled transformer. 2. The transformer shall have a continuous rating of 80% (32 MVA) of its full rating with natural cooling (ONAN). 3. The climatic conditions shall be taken into consideration with respect to the cooling system. #### 4.11.2. Radiators 1. The radiators shall be installed directly on the transformer's tank and shall be provided with shutoff valves drain plugs, vent plugs and lifting eyes. Each shut-off valve shall be provided with a lever to indicate (valve open) in line with the pipe and (valve closed) when at right angles to the pipe. 2. The radiators shall be designed and constructed such as to eliminate pockets where moisture can accumulate or which can prevent application of a continuous film of paint. 3. Flexible connections in the pipe work between the main transformer tank and the radiator headers to compensate thermal expansion or contraction of pipe where necessary shall be provided. 4. Drain plug and vent plugs in each section of cooler pipe work shall be provided. #### 4.11.3. Forced Air Cooling 1. Fans for forced air cooling shall be provided. 2. The fans and guards shall form an integral unit with their individual motors. 3. Push button operation of the cooling fans shall be possible, from the local control cabinet, and from the station control room. 4. The cooling system shall be Two group operated automatically as follows: * Group (1): When the loads exceed 80% to 100% of rated load and the temperature rise higher than the specified value. * Group (2): When the loads exceed 100% to 110% of rated load and the temperature rise higher than the specified value. 5. Tenderer shall give full description of the design, operation and maintenance of the offered forced air-cooling system with its control scheme. #### 4.11.4. Motors and Auxiliary Equipment 1. All motors shall be squirrel cage type, with rated power not less than (0.5) H.P. 2. Motors shall have a protection with automatic reset or alternatively, if the motors have individual starters, the protection may be provided in the starter circuit. On three phase motors the protective device shall trip all three phases simultaneously in the event of either a three phases; phase-to-phase, phase- to ground or open phase fault. 3. A molded case type air circuit breaker, with instantaneous trip elements shall be provided in the main supply lines. 4. An under-voltage relay to sound an alarm in the event of loss of power supply to fans shall be provided. 5. The transformer load and/or winding temperature sensor shall operate the forced stages of cooling. 6. Switches for (automatic/ manual) control of each fan circuit shall be provided. 7. Locate all cooler control auxiliary equipment in the local control cabinet. #### 4.11.5. Local Control Cabinet 1. A weatherproof control cabinet with enclosure protection IP 54, accessible from ground level shall be provided, to house the following: * Terminal blocks, for the termination of all control and auxiliary circuits plus (25%) twenty five percent spares. Terminal blocks for the owner's incoming cables shall be (stud and nut) type. * Cooler control and auxiliary equipment. * Windings and oil temperature measuring instruments. * Disconnects switch or some other visual disconnect device shall be provided in the incoming supply line. * Door actuated light, rated 220V AC. * Convenience outlet rated 220V. AC, 15A, two pole with earthing contact and its plug. * Thermostatically controlled anti-condensation heater capable of maintaining a cabinet temperature of approximately 50 °C above ambient temperature. * MCB shall be provided on the low voltage side. 2. A removable plate of adequate size in the bottom of the cabinet directly below the terminal blocks, which will be drilled in the field for cable openings. 3. All current transformer wiring shall be 4.5 mm2 copper stranded (minimum). 4. Treat interior of the cabinet with an anti-condensation coating. 5. A pocket or holder inside the cabinet for one (1) set of drawings. 6. Cabinet doors and hinged panels or barriers with devices to latch them when in the open position. Provide cabinet with padlocking facilities. ### 4.12. Transformer Construction The internal parts of the transformer such as cross sectional area of each winding, type of insulation core lamination, thickness of tank, etc. should be checked during assembly (before tanking) in the presence of EETC engineers. Two missions will arranged for EETC Engineers to attend a/m assembly, exact date will be fixed before (2) weeks from date of starting the assembly. #### 4.12.1. Core and Framework 1. The core, framework, clamping arrangement and structure of each transformer shall be mechanically robust to withstand any chocks to which they may be subjected during transport installation, service and faults. Cores shall be built of best silicon steel sheets or other quality alloy steel with same magnetic and low loss characteristics. The core sheets should be lasers treated with thickness not more than 0.27 mm. The core shall be constructed in an approved manner providing efficient cooling of its internal parts. The core joints shall be properly interleaved. 2. Precautions shall be taken to eliminate noise and vibration in the core when loaded and to diminish harmonic voltage as far as possible, particularly, the third and fifth harmonies. Full details of the construction of the core shall be given in the Tender: * The manufacturer of core steel should be reputable manufacturer, the curves of the relation between the specific iron loss and the flux density of the core steel should be submitted with tender. #### 4.12.3. Insulation 1. The insulation for transformer windings and connections shall be of class A unless otherwise approved. Contractor shall submit the test certificates and all the details of the insulation for approval. 2. Full description of the material and method of insulation shall be given in the Tender. The 66 kV winding shall have a graded insulation as defined in relevant IEC 60076-3; the 22 kV windings shall be fully insulated. The neutral points of star windings shall be insulated as specified herein. #### 4.12.4. Windings 1. The winding conductor shall be made of high conductivity electrolytic copper. The winding coils shall be designed to be mechanically and dielectrically strong and facilitate dismantling and repair. 2. The terminal and turns and tapped coils shall be provided with reinforced insulation. 3. In order to limit the short circuit current the percentage voltage impedance for Transformers shall be as specified in (S) schedules 4. The windings and connections shall be properly braced to withstand shocks and vibration during transport or due to short circuit currents. 5. The cross-sectional area of each winding to be given in schedule "G". 6. The weight of each winding to be given in schedule "G", calculation for determining these weights should be submitted. 7. Provisions shall be taken to measure and record the actual winding temperature at the hottest points by means of adequate sensors built in with a recording facility on the transformers tank. #### 4.12.5. Tank 1. The transformer tanks shall be made of best boiler plate steel with the necessary stiffness quality or equivalent subject to the approval of EETC. 2. The thickness of the tank should not be less than 10 mm. 3. The tank shall be provided with bi-directional detachable cast iron wheels provided with locking arrangement. 4. The base of the tank shall be so designed, that when the wheels are detached, it shall be possible to move the complete transformer with oil on rollers of jacks in any direction. 5. The tank's cover shall be bolted type, equipped with manholes. The location and dimensions of the manholes should facilitate the inspection of the tap changer windings and should be approved by EETC. 6. The tank shall be capable of withstanding the different conditions for treatment of insulated oil especially under full vacuum. 7. The tank shall be provided with the following fittings :- * Lifting tackles to be used for the removal of the cores and the windings. * The tank cover shall be provided with adequate manholes equipped with lifting devices. * Flanged oil drain valves, minimum two-inch. * Oil sampling cocks at the top and the bottom of the tank, minimum half-inch. * Flanged valves minimum two inch at the top and bottom opposite diagonally for connection of oil filtering machine and suitable for evacuating the tank. * Thermometer pocket for measuring the top oil temperature. * Thermostats with special pockets for the measurement of the transformer's oil and windings temperature at different points (thermal image) with remote indication contacts * Three-way cock with locking device on the connection pipe between tank and oil expansion vessel, enabling the oil passage to be shut off and the expansion vessel to be emptied. * Two Pressure relief devices with electric contact for trip on the tank cover. * Two drilled ground pads with connectors suitable for clamping a loop of stranded copper conductor ranging in size from 95mm to 300 mm mounted at diagonally opposite corners of the tank base. * A metal ladder to be attached to the transformer tank's side conveniently located to allow easy access to the gas detector relay and the top of the tank. The ladder shall be provided with a barrier having pad- locking facilities. ### 4.13 On-load Tap-changer #### 4.13.1General 1. The transformers shall be equipped with on-load tap changing equipment on the primary to maintain the secondary voltage side constant for variations of voltage on the primary side. 2. For inspection and maintenance purposes, the diverter or selector switch, which is under load, can be drawn out with its associated spring mechanism and transition resistors without having to decrease the oil level in the transformer tank. 3. The diverter switch unit shall be incorporated in a separate oil filled container. The container shall be connected to a special container or to a portion of the main expansion vessels of the transformer. A Buchholz relay of the tap changer shall be installed on the connection between the container and expansion vessel partition 4. The tap-changers shall be three phase enclosure type as approved by owner. 5. The rated current for the on load tap-changers shall be chosen 20% higher than the highest transformer winding current. The tap-changer shall be designed to withstand the routine and type tests specified in IEC60214-1 for its own rated through current. 6. The tap-changer shall sustain the normal and up-normal operating conditions of the transformer. 7. The manufacturer of the tap-hanger should be reputable manufacturer .In case the manufacturing of the tap changer is by license, the manufacturer should has the experience as requested by tender document and the type test certificates on his production should be submitted with tender. 8. The contacts of the selector and diverter switches shall with stand a number of cycles of operation corresponding to not less than five hundred thousand (500,000) operation when carrying current corresponding to 1.1 time rated current at principal tapping. Contact life curves showing the relation between the numbers of operation and rated through current should be provided. 9. Oil sampling cock at the top cover of the tap changer tank shall be provided. #### 4.13.20n-load Taps 1. On-load taps shall be controlled locally and remotely by motor operated on-load tap changing equipment of proven reliability and requiring a minimum of maintenance. 2. Overload and short-circuit characteristics shall be compatible with those of the transformers. 3. The diverter switch or the selector switch shall be incorporated in its own oil filled compartment. This oil compartment should be provided with its own oil conservator which has no connection to the conservator of the transformer on either air or oil sides. The conservator of the tap-changer compartment will be a separate portion of the transformer conservator, the oil comportment with its own conservator should be provided with the following: * Excessive oil flow relay with trip contact. * Pressure relief valve with trip contact. * Fault pressure relay with trip contacts. * Dehydrating type breather mounted at eye level, the breather shall contain a color indicator and shall be of a type in which the desiccant is not in continuous contact with the atmosphere. * Magnetic oil level gauge with alarm contacts, visible from the ground level. * Filling and oil filtering valves with dummy flanges * Drain valves with dummy flanges. * Oil sampling valves to collect the oil sample from the ground level during the operation of the transformer. * Shut off valves to be provided in the conservator pipe on the conservator side of the relays. 4. The contacts of diverter or selector switch to be copper- Tungsten. 5. If any of the on-load tap changer components are not continuously rated the drive mechanism shall be designed so that it is impossible for the tap changer to stop in any non-continuously rated position. This shall apply whether the tap changer is driven by the motor or by manual hand operation. 6. The tap changer operation shall start on a (raise) or (lower) impulse of short duration and shall (seal-in) and complete the step by itself. The duration of a signal beyond the time required for operation shall not initiate a second operation. In the event of a power failure during a tap change operation, the tap changer shall automatically be changed to the next upper or lower tap position as soon as power returns. The return of power shall not initiate a second operation. 7. Electrical limit switches and mechanical stops or declutching devices shall be incorporated to prevent over-travel beyond the maximum (raise) and (lower) positions. 8. Electrical and mechanical interlocks on the (raise) and (lower) contactors shall be provided. 9. Tap-changer motor protection shall consist of an over-current automatic air circuit breaker with manual reset. 10. Provided line drop compensation of the resistance and reactance type complete with the necessary current transformer(s). 11. Provide Current and potential terminals for test purposes 12. Provide blocking facilities to prevent the tap changer from rising if the voltage rises above an adjustable pre-set value and from lowering if the voltage falls below an adjustable pre-set value. 13. Provide loose a dial type tap position indicator, a "Manual- Automatic" switch and "Raise-Lower" push buttons or switch, for each transformer, for installation on the remote control panel. Remote tap position indication shall be of the step by-step voltage divider type with balance type indicating instrument whose accuracy is independent of normal variations in applied voltage. Local/ remote selector switch of the tape changer shall be provided at the transformer. 14. A removable handle for manual hand operation of the tap changer shall be provided. The handle shall automatically block the electrical control when in its operating position. Manual hand operation shall preferably be practicable from ground level. Alternatively, provide a platform and steps to provide access for manual hand operation. #### 4.13.3Tap Changer Control Cabinet: The tap-changer control cabinet shall be weather proof cabinet with enclosure protection IP54 accessible from the ground level. The cabinet shall have pad locking facilities a shatterproof window to be provided to permit reading of the tap position indicator. 1. The cabinet interior should be treated with anti- condensation coating; the cabinet shall house the following: * Mechanical tap position indicator with maximum and minimum reset able drag hands. The indicator shall be visible by the staff operating the tap changer manually by the handle. * Mechanical operations counter. * (Raise-Lower) push buttons or switch, for manual electric control. * (Manual-Automatic) selector switch. * (Remote-Local) selector switch. * Voltage regulating relay. * Time delay relay, adjustable from 0 to 120 seconds (if applicable). * Line drops compensation equipment. * Parallel control equipment. * Tap changer motor protection and control circuit protection devices. * Terminal blocks. * Door actuated light, rated 220 V. AC. * Handle for manual operation. ### 4.14 Oil Preservation System Oil preservation system shall be freely breathing (conservator) system, Diaphragm-type system to be offered optionally, the system should fulfil the followings: 1. Each transformer tank as well the tap-changer diverter or selector switch tank shall be fitted with an oil expansion vessel, suitable for outdoor service complete with: * Relief valve. * Magnetic oil level indicator clearly visible by an observer from ground level and equipped with remote indication contacts, to sound an alarm when the oil level drops below permissible level, the dial shall indicate the minimum, normal and maximum levels of the oil at 25 °C. * Sump, drain and dehydrating breather. 2. The oil connection pipe between the expansion vessel and the tank shall extend at least 8 cm vertically inside the expansion vessel. 3. A dehydrating type breather containing a colored indicator shall be piped with the conservator and mounted at eye level. It shall be of a type in which the desiccant is not in continuous contact with the atmosphere. ### 4.15 Bushings 1. Type of bushings should be {OIL/AIR type} O.I.P bushings as specified in section (3). Bushing shall comply with IEC standard 60137, minimum creepage distance shall be 3.5 Cm\KV, and the bushing shall be one part. 2. Each bushing shall have a rating nameplate showing the type designation and catalogue number. For smaller bushings the designation can be stamped on the flange, or be indicated on a special plate on the transformer 3. The bushing shall be made of oil filled condenser type with means to indicate oil level and power factor test taps. 4. Only one type of bushing for each insulation level shall be used on a transformer. 5. The bushing enclosure shall incorporate the following features: * The design shall facilitate easy removal of the transformer. * Compensation devices shall be included in order to meet as applicable Oil expansion and/or building and equipment tolerances. * All bushings shall be brown glazed porcelain. * All bushings shall be designed to withstand the mechanical and thermal shocks. Atmospheric conditions and temperature variations shall not affect them. * The rated current of the bushing should be not less than [1.2] times the rated current of the relative winding. * The rated thermal short-time current of the bushing should not be less than the short-circuit level, i.e., 40 kA for 2 Sec for 66 kV and 31.5 KA for 3 sec for 22 KV systems. * Each bushing should be provided with its clamp suitable for connection of incoming conductors with the transformer, the sizes of the incoming conductors will be given at the design stage. ### 4.16 Current Transformers 1. All current transformers shall comply with IEC 61869-1-2007. 2. Current transformers shall be used for winding's temperature measurements (Thermal image). 3. The current transformer shall have the secondary windings fully distributed around the core of the nominal tap. 4. The specified tap shall be referenced to the start tap. 5. Any defect in the current transformer shall not affect the transformer. 6. Facilities for easy replacement the current transformer within shortest time of shutdown of the transformer. ### 4.17 Oil For Transformers 1. The contractor shall supply the necessary oil for the first filling of the transformers. 2. These technical specifications shall be applied for the condition of transformer oil at delivery. The oil shall be of a quality that it is suitable as an insolent and coolant for transformers. 3. Tenderers shall submit with their Tenders full specifications and characteristics of the transformer's oil. 4. The oil shall be of first class quality, of high breakdown strength, low viscosity and high resistance to oxidation and shall not be deteriorated under all loading conditions. The oil shall be in conformity with the regulation of IEC, ISO, ASTM, B.S and other accepted international standard specification. The oil shall be mineral oil type free from PCBs materials. Synthetic oil types are not accepted. Transformer Manufacturers shall guarantee that the oil type can be mixed with any percent with another suitable oil type. In that case, Manufacturers should mention the names of oil and its specification, used for mixing process and guarantee that there is no serious problems shall happen for oil quality and transformers safety. 5. The oil shall be clear and completely free from solid particles, and not give a positive result when tested on corrosive sulpher. 6. The oil shall contain an oxidation inhibitor and fulfill the requirement regarding oxidation resistance in accordance with IEC 61125-2004. 7. The oil shall fulfill the requirements for class [IA] oil according to IEC 60296 last edition. 8. Electrical breakdown limits of oil should be as follows : * ≥ 40 KV / 2.5 mm: for safely operation. * 60 KV(±10% tolerance) / 2.5 mm: during factory test. * ≥ 70 KV/2.5 mm: after purification at site. ### 4.17.9 Other Properties as follows : * Density at 20 °C: max 0.895 kG/dm³ (ISO 3675) * Kinematics viscosity at 40 °C: max 16.5 mm² /S (ISO 3104) * Kinematics viscosity at -15 C: max 800 mm² /S (ISO 3104) * Flash-point: min. 140 °C (ISO 2719) * Acid value, mg KOH/g: max 0.03 (IEC 296) * Sulphur content, total: non-corrosive (ISO 5662) * Surface tension against water at 25 °C: min 45X10-3 N/m (ISO 6295) * Electrical breakdown limit after purification. min 70 kV (IEC 60156) * Pour point: Max (-30°C) (spherical electrodes ISO 3016) * Dielectric losses tan delta: * At 20 C max.: 0.001 (IEC 60247) * At 95C max.: 0.005 (IEC 60247) * Induction time when determining oxidation Resistance.: Min. 120 hours (IEC 61125) #### 4.17.10 Packing: 1. Container: The transformer oil shall be delivered in filled drums. These drums shall be new, of best quality and in general of a type normally used in the oil branch. Internal surface of the drums shall be thoroughly cleaned and completely free from any kind of particles. External surface shall be treated against corrosion, painted with oil and weather resisting paint. The drum jacket shall be painted in blue, and the end in white. 2. The drums shall be stenciled on bung sides with goods designation, Consignee name and address, serial number and the oil and drum net weights. These markings shall be of oil and weather- resisting black paint. #### 4.17.10