This document and its content, is for authorized company use onlyIn this document the IEC terminology is used for Earth instead of the ANSI terminology which is Ground.Requirements: Transformers Classification: Internal Project development, Requirements, TR3123, Version 3.02 Page 7 of 24 Printed: 15/05/2023 14:42:48SR-47883 - Harmonic currents in e.g. converter transformers will increase losses and temperatures of the windings and nearby steel parts of the transformer. The effect of harmonic currents shall be taken into account according to IEC 61378-1 or IEEE C57.18.10 respectively.SR-47884 - Ancillary components and construction features such as bushings, cable-end connections, tap-changing devices, internal leads, liquid expansion space etc., shall be dimensioned in a manner that will not limit the loading to less than the capability of the windings.SR-47887 - One of the windings shall be delta connected. For a stabilizing winding both ends of at least one corner of the delta shall be brought out on separate bushings.SR-47888 - For transformers with specifications based on IEC: The insulation level for low voltage transformers shall be according to U m ≤ 1.1 kV given by table 3 in section 12.1 in IEC 60076-11.SR-47889 - Increased losses due to harmonic currents shall be taken into account in thermal dimensioning in accordance with IEC 61378-1 or IEEE C57.18.10 respectively.SR-47892 - The rated current of the neutral point shall be equal to the rated current of the corresponding transformer windings terminals.SR-47893 - Where a Neutral Earth Resistor (NER) is specified in datasheet, then the resistor shall be connected between the neutral point and the earth bar. A current transformer shall beprovided for measuring the neutral point current. The current transformer and the NER shall be mounted in a separate purpose made enclosure mounted outside of the transformer housing.SR-47894 - The CT shall be according to IEC 61869-2 or IEEE C57.13 respectively. All secondary leads shall be brought out to terminal blocks in the cabinet. The terminals shall be provided with short-circuiting links.SR-47895 - The cable for connection of the NER to the transformer neutral point must be dimensioned for overvoltages due to e.g. failures in other part of the network.SR-47898 - The core sheets of the magnetic circuit of transformers exceeding 16 MVA shall be bonded to the core clamping structure through at least one removable core-insulation test link. The link shall be placed in an accessible position. With the bond removed, the core sheets of the magnetic circuit shall be insulated from the core clamping and all structural parts.SR-47903 - All signals from instruments, Current Transformers CTs, sensors etc. shall be connected in a separate cabinet. Internal wiring shall be according to TR3120 section 4.10.SR-47904 - Light fixture and space heaters inside cabinets shall be according to TR3120 section 4.17.SR-47905 - Earthing of the transformer shall be according to TR3120 section 4.8 (high voltage equipment).SR-47906 - The transformer shall be provided with a minimum of two earth terminals for connection to the external earth grid. The terminals shall be located on opposite sides of thetransformer to enable easy connection to the earth grid. Both terminals shall be boss type to enable connection via lugs.SR-47907 - For transformers with specifications based on IEEE, 2 hole lugs shall be provided.SR-47910 - The rating plate shall be in accordance with requirements in :SR-47915 - Isocyanate-based products (e.g. polyurethanes) or products that release di- isocyanates when heated shall not be used.SR-47920 - The plus tolerance for the noise level is zero, i.e. the measured noise level shall be equal to or below the stated limit.SR-47926 - For transformers based on IEEE specifications the insulation paper of the windings shall be thermally upgraded IEC 60076-1 or IEEE C57.12.00 and IEEE C57.12.90 respectively.See requirements for high temperature design in section 3.5.3.SR-47928 - The rated withstand voltages for transformer windings shall be selected to the highest value as given in table 2 in IEC 60076-3. Values indicated with “note a” in table 2 in IEC 60076-3 shall not be used.SR-47932 - Silicone type oil shall not be used for transformers with On-Load Tap Changer, OLTC, due to the poor lubrication of the tap contacts.SR-47933 - Use of insulation liquids for allowing temperatures above 105°C, e.g. listed in /9/, shall not be used for transformers with U m equal to or above 72,5 kV or 69 kV for IEC or IEEE based specifications due to the limited experience of dielectric withstand capability of such insulating liquids.SR-47942 - The yearly average ambient cooling medium temperature is stated in the datasheet. Otherwise the yearly average temperature shall be as stated in IEC 60076-2 or IEEE C57.12.00 respectively.SR-47943 - In case of water cooling, the coolers shall be of double wall design, and shall be equipped with a leakage monitoring system. All water exposed materials in the cooler shall be compatible with the cooling water.SR-47944 - Plate and Frame Heat Exchangers shall be according to cl 2 in TR0041. The flanges for the water side of the heat exchanger shall be according to cl 2 in TR2000.SR-47947 - The average temperature rise of the transformer windings at rated power shall not exceed 65 K, and the top oil temperature shall not exceed 60 K. Reference is made to IEC 60076-1 or IEEE C57.12.00 and IEEE C57.12.90 respectively.SR-47948 - If the yearly average temperature of the external cooling medium given by thedatasheet exceeds the stated yearly average temperature from the standards (IEC 60076-1 or IEEE C57.12.00 and IEEE C57.12.90 respectively), then the average temperature rise limit of the transformer windings and top oil shall be reduced by the same amount as the excess. Three examples are given for yearly average external cooling medium excess temperatures of 0 K, 10 K and 20 K respectively.SR-47952 - The high temperature design shall as a minimum be based on hybrid insulation system. The average temperature rise of the transformer windings at rated power shall not exceed 95 K, and the top oil temperature shall not exceed 60 K. Reference to other requirements in IEC 60076-14 or IEEE 1276 respectively..SR-47953 - Minimum thermal class for the high-temperature solid insulation shall be 155 °C.SR-47954 - If the yearly average temperature of the external cooling medium from the datasheet exceeds the stated yearly average temperature from the standards (IEC 60076-1 or IEEE C57.12.00 and IEEE C57.12.90 respectively), then the average temperature rise limit of the transformer windings and top oil shall be reduced by the same amount as the excess.SR-47957 - For air insulated bushings the IP code of the protective housing for cable terminations shall be according to section 3.1, if not otherwise stated.SR-47958 - For plug-in type bushing or equivalent touch proof solution, a portable earthing device shall be delivered, if not otherwise stated.SR-47959 - It shall be provision for measuring voltage at the bushing to be able to check if theTable 1: Allowed temperature rises of average windings and top oilSR-47960 - The transformer bushings shall be of outdoor type, and shall comply with IEC 60137 or IEEE C57.19.00 respectively..SR-47966 - The transformer skid base shall be designed for handling of the liquid filled transformer.SR-47967 - Jacking pads should be available on the transformer tank to allow jacking of the liquid filled transformer.SR-47968 - There shall be valves provided for at least:Liquid filling, draining and venting of all liquid volumes. Liquid sampling from top of the tank. The valve shall be placed within reach from the floor such that there is no need to use of scaffolding or a ladder for sampling. Isolating external cooling equipment from transformer tank. Isolating each compartment of the conservator tank from the transformer tank.SR-47969 - A moisture-removing breather shall be provided for each chamber of the oil conservator tank.SR-47970 - Transformers with U m equal to or above 24 kV shall have a diaphragm-type oil preservation system to avoid direct contact between the transformer oil and air. A flexible diaphragm or bladder shall be used for this purpose.SR-47971 - The liquid conservator shall have a separate compartment for the OLTC diverter switch oil if OLTC is part of the transformer. For this compartment a free breathing system can be used.SR-47972 - 316L stainless steel shall be used for fasteners (screws, bolts, nuts, etc.) up to and including a diameter of 10 mm. For diameters above 10 mm fasteners shall be hot dipgalvanised in accordance with ASTM A153 or coated with PTFE with anticorrosion pre- treatment such as cermet.The requirement for fasteners does not apply to fasteners inside the transformer tank.SR-47976 - It shall be possible to measure voltage at the terminals before removal of the protective housing of the cable terminals.SR-47981 - The following non-routine tests listed in IEC 60076-1 or IEEE C57.12.00 and IEEE C57.12.90 respectively shall be performed:Temperature-rise test for transformers rated 16 MVA and above. Determination of capacitances windings-to-earth, and between windings for all converter transformers Audible sound level.SR-47982 - If several identical transformers are ordered, the non-routine test should be performed on one transformer only.SR-47983 - A dissolved gas in oil analysis shall be performed according to IEC 60076-2 or IEEE C57.12.00 respectively.SR-47988 - The minimum winding insulation class shall be:SR-47989 - Corresponding winding hot spot temperature shall be in accordance with IEC 60076-12 or IEEE C57.12.01 respectively.SR-47990 - The windings shall be solid-casted or VPI.SR-47991 - All terminals shall be of copper type. This also applies when aluminium windings is specified.SR-47994 - OCTC tapping selection should be made by the use of bolted links instead of off- circuit tap-changersSR-47995 - If OLTC is specified, then the corresponding motor drive cabinet shall be in accordance with IEC 60214-1 or IEEE C57.131 respectively.SR-48000 - The stated yearly average temperature of the external cooling medium is 20 °C for IEC and 30 °C for IEEE based specifications. The corresponding average temperature rise of the transformer windings at rated power shall not exceed 100 K for IEC and 90 K for IEEE based specifications. Reference is made to IEC 60076-11 or IEEE C57.12.01 and IEEE C57.12.91 respectively.SR-48001 - If the yearly average temperature of the external cooling air given by the datasheet exceeds the stated yearly average temperature from the standards IEC 60076-11 or IEEE C57.12.01 and IEEE C57.12.91 respectively, then the average temperature rise limit of the transformer windings shall be reduced by the same amount as the excess.SR-48005 - The IP rating for the protective housing shall be according to requirements in section 3.1.SR-48006 - Doors and panels shall be hinged. There shall be isolating bars behind the doors. The bars shall be coloured yellow and black (zebra stripes) if not otherwise required by national regulation.SR-48007 - Transformer enclosures for ratings equal to or greater than 315 kVA should be equipped with windows that allow thermo graphic inspection.SR-48016 - The following non-routine tests shall always be performed (ref IEC 60076-11 or IEEE C57.12.01 and IEEE C57.12.91 respectively):Temperature-rise test together with the planned protective housing unless otherwise agreed upon. Partial discharge measurement special test. Determination of capacitances windings-to-earth and between windings for all converter transformers.SR-48017 - If several identical transformers are ordered, the non-routine test should be performed on one transformer only.Shall (requirement) Requirement strictly to be followed in order to confirm to the document and from which no deviation is permitted, unless a deviation permit is approved.Should (recommendation) Indicates that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action ispreferred but not necessarily required, or that (in the negative form) possibility or course of action is deprecated but not prohibited.May Indicates a course of action permissible within the limits of the document.Can Statements of possibility and capability, whether material, physical or causal. AC Alternating current AF Air Forced AN Air Natural Converter transformer Transformer feeding a converter load CT Current Transformer DEH Direct Electric Heating IP Ingress Protection NER Neutral Earth Resistor OCTC Off Circuit Tap Changer OFWF Oil Forced Water Forced OLTC On Load Tap Changer ONAF Oil Natural Air Forced ONAN Oil Natural Air NaturalGeneral: Editorial changes, updated IEC / IEEE references and added references to TR3120 Section 2.1: Deleted requirements for base case transformers Section 2.3: Deleted requirement for uniform winding insulation and included reference to IEC 61378-1 Section 2.5: Removed requirement for 110 % core dimensioning is required for all type of transformers Section 2.9: Non-technical information removed Section 2.11: New section added for vibration dampers Section 3.6: Updated text and that bushing type will be described in datasheet Section 3.7: Removed requirement for CT for thermal image Section 4.3: The transformer core shall be dimensioned for continuous operation at 110 % of rated voltage referred to the principal tapping and rated power. Section 4.6: Fire class updated from F0 to F1SR-48025 - Latest issue of the referred document shall be used unless otherwise agreed.Other recognized standards may be used provided it can be shown that they meet or exceed the requirements and guidelines of the standards referenced below.Note that references in this specification (e.g. references to clause numbers in standards) are based on year of issue as listed below.Table 3: Standards that are the basis for transformer specificationIEC IEEE 2011 IEC 60076-1 Power transformers, Part 1: General 2010 2010 IEEE C57.12.00 IEEE C57.12.90 General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers 2011 1998 IEC 61378-1 IEEE C57.18.10 Converter Transformers, Part 1: Transformers for industrial applications Practices and Requirements for Semiconductor Power Rectifier Transformers