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Engineering StandardSAES-P-121Transformers and Reactors4 June 2013Document Responsibility: Electrical Substations Equipment Stds CommitteeSaudi Aramco DeskTop StandardsTable of ContentsPrevious Issue: 30 October 20121Scope. 22Conflicts and Deviations. 23References. 24Definitions. 35General. 46Sizing. 67Installation. 88Protection. 9Next Planned Update: 4 June 2018Page 1 of 19Primary contact: Al-Ghamdi, Mohammed Ahmed on 966-3-8809667Copyright Saudi Aramco 2013. All rights reserved.

Document Responsibility: Electrical Substations Equipment Standards CommitteeIssue Date: 4 June 2013Next Planned Update: 4 June 20181SAES-P-121Transformers and ReactorsScopeThis Standard prescribes the minimum mandatory requirements for the design andinstallation of transformers, reactors and instrument transformers. This document maynot be attached to nor made a part of purchase order.2Conflicts and Deviations2.1Any conflicts between this standard and other applicable Saudi AramcoEngineering Standards (SAESs), Materials System Specifications (SAMSSs),Standard Drawings (SASDs), or industry standards, codes, and forms shall beresolved in writing by the company or buyer representative through theManager, Consulting Services Department of Saudi Aramco, Dhahran.* Examples of MSAERs are Saudi Aramco Materials System Specifications (SAMSSs),Engineering Standards (SAESs) and Standard Drawings (SASDs).32.2Direct all requests to deviate from this standard in writing to the company orbuyer representative, who shall follow internal company procedure SAEP-302and forward such requests to the Manager, Consulting Services Department ofSaudi Aramco, Dhahran.2.3The designation “Commentary” is used to label a sub-paragraph that containscomments that are explanatory or advisory. These comments are not mandatory,except to the extent that they explain mandatory requirements contained in thisSAES.ReferencesThe selection of material and equipment, and the design, construction, maintenance, andrepair of equipment and facilities covered by this standard shall comply with the latestedition of the references listed below unless otherwise noted.3.1Saudi Aramco ReferencesSaudi Aramco Engineering ProcedureSAEP-302Instructions for Obtaining a Waiver of a MandatorySaudi Aramco Engineering RequirementSaudi Aramco Materials System Specifications14-SAMSS-531Power Transformers14-SAMSS-533Three-Phase Dry-Type Power Transformers14-SAMSS-534Overhead-Type Distribution TransformersPage 2 of 19

Document Responsibility: Electrical Substations Equipment Standards CommitteeIssue Date: 4 June 2013Next Planned Update: 4 June 2018SAES-P-121Transformers and Reactors14-SAMSS-536Pad-Mounted Three-Phase DistributionTransformers16-SAMSS-504Indoor Metal-Clad Switchgear: 1 to 38 kVSaudi Aramco Engineering Standards3.2SAES-P-100Basic Power System Design CriteriaSAES-P-104Wiring Methods and MaterialsSAES-P-113Motors and GeneratorsSAES-P-114Power System and Equipment ProtectionSAES-P-116Switchgear and Control EquipmentSAES-P-119Onshore SubstationsIndustry Codes and StandardsAmerican National Standards InstituteANSI C2National Electrical Safety Code (NESC)ANSI C37.46Specification for Power Fuses and FuseDisconnecting SwitchesANSI C37.91Guide for Protective Relay Applications to PowerTransformersANSI C57.12.11Guide for Installation of Oil-Immersed TransformersANSI C57.13Requirements for Instrument TransformersANSI C57.16Requirements, Terminology and Test Code forCurrent Limiting ReactorsANSI C57.91IEEE Guide for Loading Mineral-Oil-ImmersedTransformersANSI C57.94Recommended Practice for Installation, Application,Operation, and Maintenance of Dry-Type GeneralPurpose Distribution and Power TransformersANSI/NFPA 70National Electrical Code (NEC)IEEE C57.116Guide for Transformers Directly Connected toGeneratorsNational Electrical Manufacturers AssociationNEMA ST 1Specialty TransformersPage 3 of 19

Document Responsibility: Electrical Substations Equipment Standards CommitteeIssue Date: 4 June 2013Next Planned Update: 4 June 20184SAES-P-121Transformers and ReactorsDefinitionsPower Transformer: is equipment manufactured per 14-SAMSS-531.Dry-Type Power Transformer: is equipment manufactured per 14-SAMSS-533.Overhead-Type Distribution Transformer: is equipment manufactured per14-SAMSS-534.Pad-Mounted Distribution Transformer: is equipment manufactured per14-SAMSS-536.High Voltage (HV): Voltages 1000 V and greater. When used to describe transformerwindings, can also be used as a relative term to differentiate the winding(s).Low Voltage (LV): Voltages less than 1000 V. When used to describe transformerwindings, can also be used as a relative term to differentiate the winding(s).Instrument Transformer: is equipment manufactured per ANSI C57.13, unlessspecified otherwise in an individual SAMSS.Current Transformer (CT): a type of Instrument Transformer.Voltage Transformer (VT): a type of Instrument Transformer.Control Transformer: is equipment manufactured per NEMA ST 1, unless specifiedotherwise in an individual SAMSS.Current-Limiting Reactor: is equipment manufactured per ANSI C57.16.SAMSS: Saudi Aramco Materials System SpecificationApproval: written approval of the Coordinator, Electrical Systems Division,Consulting Services Department, Saudi Aramco.Site Rating: Actual operating rating of the equipment based upon de-rating factor inTable 1 of this standard.ONAN: Oil Natural-Air NaturalONAF: Oil Natural-Air ForceOFAF: Oil Force-Air Force5General5.1Terms in bold font are defined within Section 4.Page 4 of 19

Document Responsibility: Electrical Substations Equipment Standards CommitteeIssue Date: 4 June 2013Next Planned Update: 4 June 2018SAES-P-121Transformers and Reactors5.2Unless indicated otherwise transformer ratings shown are non-forced cooledratings at 65 C temperature rise.5.3Power transformers and Distribution transformers shall be the two-windingtype. Normally, two-winding power and distribution transformers shall bedelta-connected on the supply side and wye-connected on the load side.Exceptions:5.41.Other winding angular displacement between high-voltage and low-voltageterminal voltages may be specified with approval by the Electrical SubstationsEquipment Standards Committee Chairman.2.Generator Step up transformer shall be delta-connected on the generator (lowvoltage) side and wye-connected on the transmission (high voltage) side.Three winding transformer shall not be used.Exception to 5.4:If approval is obtained.5.5The load tap changing requirements for step-down transformers shall bedetermined by the project requirements and specified in the SAMSS DataSchedules.5.6Intertie transformers that may carry power flow in either direction shall beprovided with a HV load tap changer.5.7When specified all load tap changers shall be equipped for remote operation.5.8Bids for Power transformers shall be evaluated in accordance with vendorinstructions in 14-SAMSS-531 and the following:Formula #1 C P (A * Li) (B * Lc) Where:C total evaluated present-value price used for bid comparisonpurposes including life cycle cost of losses;P transformer quoted price delivered to site;A cost/kW of no-load loss as stated on the SAMSS Data Schedules;Li guaranteed no-load loss at rated voltage, in kW;B cost/kW of load loss as stated on the SAMSS Data Schedules;Lc guaranteed load loss at the self-cooled rating, in kW, at referencedtemperature.Page 5 of 19

Document Responsibility: Electrical Substations Equipment Standards CommitteeIssue Date: 4 June 2013Next Planned Update: 4 June 2018SAES-P-121Transformers and ReactorsThe values of loss constants A and B shall be calculated by the followingformulas and included in the SAMSS Data Schedules:Formula #2 A E1 * T1 * [(1 i)n – 1)] / [i * (1 i)n ]Formula #3 B A * 0.49 /kWCurrentUtilization FactorsWhere:E the energy cost must be obtained from Facilities Planning DepartmentT1 number of hours per yeartransformer is energized8766 HRSi interest rate or rate of return on investment5.9%n number of years for capitalization of losses20 YRSCommentary Note:The multiplier 0.49 is the load factor determined at 70% average load of thetransformer by dividing the (average load)² by the (rated load)².5.9Dry-Type TransformersTransformers shall have the following characteristics:a)Windings and all main circuit conductors shall be copper.b)Windings shall be encapsulated with solid insulation or vacuum pressureimpregnated.c)Shall fully comply with either of the following:d)6i)IEC 60726ii)UL listed which requires the transformer be manufactured inaccordance with applicable NEMA, ANSI, UL and IEEE standards.Enclosure material and protection are listed in SAES-P-104.Sizing6.1Power and Distribution Transformers6.1.1Transformers shall be supplied with ANSI Standard preferred kVARatings at usual service conditions, unless specified otherwise onSAMSS Data Schedule-1.Page 6 of 19

Document Responsibility: Electrical Substations Equipment Standards CommitteeIssue Date: 4 June 2013Next Planned Update: 4 June 2018SAES-P-121Transformers and Reactors6.1.2The minimum ONAN self-cooled kVA rating of each ONAN/ONAFtransformer shall be equal to the maximum operating load plusprojected future load. The projected future load shall be defined as perproject DBSP requirement.6.1.3Captive transformers shall be limited to motors rated 7500 HP andlarger. Captive transformers rating shall be selected by the motorvendor.6.1.4For transformers that are self-cooled only, a 10% load growth factorshall be added to the calculated load (maximum operating load plusprojected future load).6.1.5The forced-cooled ONAF site rating of each transformer serving adouble-ended substation shall be capable of feeding the entireoperating load of both buses with the bus-tie breaker closed.6.1.6Forced-air cooling fans and controls shall be provided on alltransformers rated 2500 kVA or larger, and shall not be supplied ontransformers rated less than 2500 kVA6.1.7For transformers with ONAN ratings of 90 MVA or larger two stagesof forced cooling are acceptable. The forced cooling may be forced-airONAF and/or forced-oil-air (OFAF). Two stages of cooling shall notbe supplied on transformers less than 90 MVA.6.1.8The self-cooled kVA rating of power transformers shall be de-rated forcontinuous operation at higher than usual ambient temperatures inaccordance with ANSI loading guides. The ambient temperatures inthe Saudi Aramco operating areas are listed in SAES-P-100.6.1.9The derated kVA ratings shall satisfy the load requirements ofparagraph 6.1.1 through paragraph 6.1.8. All attachments andaccessories such as bushings, instrument transformers, and surgearresters shall be compatible with the site ambient temperatures andnot limit the transformer kVA rating at site temperatures.6.1.10When transformers are operated in parallel, the total circulating currentshall not exceed 10% of the rated current of the lowest kVA ratedtransformer.6.1.11The maximum allowable percentage deratings for various siteinstallations and transformer types and sizes shall be in accordancewith Table 1 below. Manufacturers shall supply equipment that isdesigned to perform according to the ANSI loading guides.Page 7 of 19