C9-02Dry-Type TransformersLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.(Reaffirmed 2007)Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.CSA Standards Update ServiceC9-02October 2002Title:Dry-Type TransformersPagination:41 pages (vi preliminary and 35 text), each dated October 2002Automatic notifications about any updates to this publication are available. To register for email notifications, and/or to download any existing updates in PDF, enter the Online Store at www.csa.ca and click on My Account on the navigation bar.The List ID for this document is 2013852. To receive printed updates, please complete and return the attached card.EName OrganizationAddressCityProvince/StateCountryPostal/Zip CodeEmailC9-02Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.AffranchirsuffisammentPlace Stamp HereASSOCIATION CANADIENNE DE CANADIAN STANDARDSNORMALISATION ASSOCIATIONBUREAU CENTRAL DE LINFORMATION CONSOLIDATED MAILING LIST5060, SPECTRUM WAY, BUREAU 100 5060 SPECTRUM WAY, SUITE 100MISSISSAUGA ON L4W 5N6 MISSISSAUGA ON L4W 5N6CANADA CANADALicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.CSA StandardC9-02Dry-Type TransformersRegistered trade-mark of Canadian Standards AssociationPublished in October 2002 by Canadian Standards AssociationA not-for-profit private sector organization5060 Spectrum Way, Suite 100, Mississauga, Ontario, Canada L4W 5N61-800-463-6727 416-747-4044Visit our Online Store at www.csa.caLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.ISBN 1-55397-063-2Technical Editor:John ONeill Canadian Standards Association 2002All rights reserved.No part of this publication may be reproduced in any form whatsoeverwithout the prior permission of the publisher.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit. Canadian Standards Association Dry-Type TransformersiiiOctober 2002ContentsTechnical Committee on Dry-Type Transformers vPreface vi1Scope 12Reference Publications 13Definitions 24Type Classifications 45Mechanical Features 55.1Enclosures 55.2Provisions for Lifting and Mounting 65.3Terminal Arrangements 65.4Spacings 75.5Grounding 76Marking 86.1General 86.2Identification of Windings 86.3Marking of Terminals 97Electrical Features 97.1Temperature and Insulation 97.2Kilovolt-Ampere Ratings 107.3Voltage Ratings 117.4Polarity 117.5Angular Displacement 117.6Standard Percentage Impedance 117.7Parallel Operation 117.8Audible Sound Levels 117.9Dielectric Withstand 117.9.1General 117.9.2Applied Potential (Low Frequency) 117.9.3Induced Potential 127.9.4Basic Impulse Insulation Level 127.9.5Single-Phase Transformers 127.10Partial Discharges (Corona) 127.11Short-Circuit Capability under Fault Conditions 128Tests 148.1General 148.2Wave Form 148.3Type Tests 148.3.1General 148.3.2Specimens 148.3.3Temperature Test 14Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards AssociationivOctober 20028.3.4Sound-Level Test 158.3.5Partial Discharges (Corona) 158.3.6Basic Impulse Insulation Level (BIL) 158.4Production Tests 168.4.1General 168.4.2Voltage Ratio 168.4.3Tolerance for Voltage Ratio 168.4.4Tolerance for Losses and Exciting Current 168.4.5Load Losses and Impedance Voltage 178.4.6Efficiency 178.4.7Tolerance for Impedance 178.4.8Regulation 178.4.9Dielectric Tests 17Tables 19Figures 28AnnexesA (informative) Guideline for Application, Installation, and Maintenance of Dry-Type Transformers 30B (informative) Guideline for Overvoltage and Overcurrent Protection of Dry-Type Transformers 34C (informative) Guideline for Interpretation of Voltage and Current Oscillograms 35Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit. Canadian Standards Association Dry-Type TransformersvOctober 2002Technical Committee on Dry-TypeTransformersD.S. Patel Hammond Power Solutions Inc., ChairGuelph, OntarioJ.G. Lackey Ontario Power Generation Inc., Vice-ChairToronto, OntarioP. Chung Mulvey & Banai International Inc.,Toronto, OntarioS. Hasserjian Rex Manufacturing,Etobicoke, OntarioR. Jackson Blenkhorn and Sawle Ltd.,St. Catharines, OntarioP. Lynch Power Line Systems Inc.,Markham, OntarioJ.P. Neu Electro-Federation Canada,Mississauga, OntarioL. Nova Marcus Transformer of Canada Ltd.,Montral, QubecC. Paradis ABB Inc.,Varennes, QubecG. Pregent The Delta Group xfo,Boucherville, QubecE. Tan Atlas Transformer Inc.,Mississauga, OntarioM.G. Theriault Expertises Electro-Tech Inc.,Montral, QubecK. Walsh London Hydro,London, OntarioJ. ONeill CSA, Project ManagerMississauga, OntarioLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards AssociationviOctober 2002PrefaceThis is the fourth edition of CSA C9, Dry-Type Transformers.It includes numerous changes to improve theclarity of clauses and to update the Standard.It supersedes the previous editions published in 1981,1977, and 1966.Further requirements for dry-type transformers, in accordance with the Canadian Electrical Code, can befound in CSA C22.2 No. 47.This Standard was prepared by the Technical Committee on Dry-Type Transformers, under thejurisdiction of the Strategic Steering Committee on Power Engineering and ElectromagneticCompatibility, and has been formally approved by the Technical Committee.October 2002Notes:1)Use of the singular does not exclude the plural (and vice versa) when the sense allows.2)Although the intended primary application of this Standard is stated in its Scope, it is important to note that it remainsthe responsibility of the users of the Standard to judge its suitability for their particular purpose.3)This publication was developed by consensus, which is defined by CSA Policy governing standardization Code ofgood practice for standardization as substantial agreement.Consensus implies much more than a simple majority, butnot necessarily unanimity.It is consistent with this definition that a member may be included in the Technical Committeelist and yet not be in full agreement with all clauses of this publication.4)CSA Standards are subject to periodic review, and suggestions for their improvement will be referred to the appropriatecommittee.5)All enquiries regarding this Standard, including requests for interpretation, should be addressed to Canadian StandardsAssociation, 5060 Spectrum Way, Suite 100, Mississauga, Ontario, Canada L4W 5N6. Requests for interpretation shoulda)define the problem, making reference to the specific clause, and, where appropriate, include an illustrative sketch;b)provide an explanation of circumstances surrounding the actual field condition; andc)be phrased where possible to permit a specific yes or no answer. Committee interpretations are processed in accordance with the CSA Directives and guidelines governingstandardization and are published in CSAs periodical Info Update, which is available on the CSA Web site at www.csa.ca.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit. Canadian Standards Association Dry-Type Transformers1October 2002C9-02Dry-Type Transformers1Scope 1.1This Standard applies to single- and 3-phase dry-type transformers, including those with cast or resinencapsulated coils, that are within the limits of the electrical ratings listed in Clauses 7.2 and 7.3, andthat are intended for use in accordance with the service conditions for dry-type transformers outlined inAnnexes A and B. Note:For information on the loading of dry-type transformers, see ANSI/IEEE C57.96.1.2 This Standard deals with the standardization of voltage ratings, kVCA capacities, other electrical features,certain mechanical features, and test procedures. 1.3This Standard does not apply to transformers designed solely for test purposes, rectifier transformers,welding transformers, furnace transformers, instrument transformers, motor-starting autotransformers, orany other special purpose transformers. 1.4The word transformer, when used in this Standard, refers to a dry-type transformer unless otherwisespecifically stated. 2Reference Publications This Standard refers to the following publications and, where such reference is made, it shall be to theedition listed below, including all amendments published thereto.Note:The editions listed below may be replaced by newer editions during the life of this referencing Standard.Users ofthis Standard are encouraged to investigate the possibility of applying the most recent editions. CSA (Canadian Standards Association)C22.1-02Canadian Electrical Code, Part IC22.2 No. 0.12-M1985 (R1999)Wiring Space and Wire Bending Space in Enclosures for Equipment Rated 750 V or LessC22.2 No. 47-M90 (R2001)Air-Cooled Transformers (Dry Type)CAN/CSA-C22.2 No. 94-M91 (R2001)Special Purpose EnclosuresCAN3-C235-83 (R2000)Preferred Voltage Levels for AC Systems, 0 to 50 000 VLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association2October 2002ANSI/IEEE (American National Standards Institute/Institute of Electrical and Electronics Engineers)C57.96-1999Guide for Loading Dry-Type Distribution and Power TransformersC57.98-1993Guide for Transformer Impulse TestsC57.110-1998Recommended Practice for Establishing Transformer Capability When Supplying Nonsinusoidal Load CurrentsIEEE (Institute of Electrical and Electronics Engineers)C57.12.01-1998General Requirements for Dry-Type Distribution and Power TransformersC57.12.91-2001Test Code for Dry-Type Distribution and Power Transformers3Definitions The following definitions apply in this Standard: Angular displacement in a polyphase transformer the time angle, expressed in degrees,between the line-to-neutral voltage of a specified high-voltage terminal and the line-to-neutral voltage ofthe corresponding low-voltage terminal (e.g., H X ), which can be 0 or 30 as shown in Figure 1.1 1Autotransformer a transformer in which part of one winding is common to both primary andsecondary circuits associated with that winding.Common or shunt winding of an autotransformer that part of the autotransformer windingthat is common to both primary and secondary circuits.Efficiency of a transformer the ratio of a transformers power output to its total power input.Equivalent two-winding kVCA a)For an autotransformer, the output kVCA multiplied by the series winding voltage and divided by thesum of the series and common winding voltages.b) For a two-winding transformer, the nameplate kVCA.Exciting current of a transformer the current that flows in any winding used to excite thetransformer at rated voltage when all other windings are open-circuited.It is usually expressed as apercentage of the rated current of the winding in which it is measured.Impedance voltage of a transformer the voltage required to circulate rated current at ratedfrequency through one winding when another winding is short-circuited and the windings areconnected for rated voltage operation.It is usually expressed as a percentage of the rated voltage of thewinding in which the voltage is measured.Insulation voltage class the grouping of nominal operating voltages into class levels as a basis forassigning standard dielectric tests to each class.The classification is based on phase-to-phase voltage forungrounded delta or wye systems and on phase-to-ground voltage for grounded wye systems.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit. Canadian Standards Association Dry-Type Transformers3October 2002kVCA rating of a transformer the output on which specified maximum values of loss, regulation,and temperature rise characteristics are based, assuming the output to be at rated voltage.Load losses of a transformer those losses that occur as a result of carrying of load.Note:Load losses include I R losses in the windings due to load current and stray losses due to stray fluxes in the2windings, core clamps, etc., and to circulating currents, if any, in parallel windings. No-load losses of a transformer those losses that occur when the transformer is excited at ratedvoltage and frequency, but not supplying load.Note:No-load losses include core loss, dielectric loss, and copper loss in the windings due to exciting current.(See Clause 8.2.)Partial discharge (corona) extinction voltage the rms voltage at which partial discharge abovethe specified intensity level is no longer observed as the voltage is decreased from a level above thecorona inception voltage.Partial discharge (corona) inception voltage the lowest rms voltage at which partial discharge above the specified intensity level is observed to occur as the voltage is increased.Polarity, additive or subtractive see Relative lead polarity of a transformer.Regulation of a transformer the change in secondary voltage, expressed as a percentage of ratedsecondary voltage, that occurs when the rated kVCA output at a specified power factor is reduced to zero,the primary impressed terminal voltage being held constant.Note:In the case of multiwinding transformers, the loads on all windings are to be reduced from rated kVCA to zerosimultaneously. Relative lead polarity of a transformer a designation of the relative instantaneous directions ofcurrent in the leads of a transformer.Notes:1)Primary and secondary leads are said to have the same polarity when, during most of each half cycle, at a giveninstant, the current enters an identified or marked primary lead and leaves the similarly identified or marked secondary leadin the same direction as though the two leads formed a continuous circuit. 2)The relative lead polarity of a single-phase transformer may be either additive or subtractive.When the lowestnumbered H and the lowest numbered X terminations are connected together (Hand Xin Figure 2), and voltage is1 1applied across one of the windings (Hand Hor Xand X ),1 2 1 2a) polarity is additive if voltage between the highest numbered H and highest numbered X (between Hand X ) is greater2 2than the voltage between the highest and lowest numbered H winding (Hand H ); and2 1b) polarity is subtractive if voltage between the highest numbered H and highest numbered X (between Hand X ) is less2 2than the voltage between the highest and lowest numbered H winding (Hand H ).When more than two windings are2 1used, the same relationship applies between any set of windings.3)The relative lead polarity is indicated by identification marks on primary and secondary leads of like polarity or by otherappropriate identification. 4)The polarity of a polyphase transformer is fixed by the internal connections between phases as well as by the relativelocation of leads; it is usually designated by means of a vector diagram showing the angular displacement of windings anda sketch showing the marking of the leads.The vector lines of the diagram represent induced voltages, and the recognizedcounter-clockwise direction of rotation is used.The vector representing any phase voltage of a given winding is drawnparallel to that representing the corresponding phase voltage of any other winding under consideration. Series winding of an autotransformer that portion of the autotransformer winding that is notcommon to both the primary and secondary circuits, but is connected in series between the input andoutput circuits.System, effectively grounded a system in which the highest rms line-to-ground power frequencyvoltage on a sound phase, at a selected location, during a fault-to-ground affecting one or more phases,does not exceed 80% of the line-to-line power frequency voltage that would be obtained, at the selectedlocation, with the fault removed.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association4October 2002Note:A value not exceeding 80% is obtained approximately when, under all system conditions, the ratio of zero-sequencereactance to positive-sequence reactance is positive and less than 3, and the ratio of zero-sequence resistance topositive-sequence reactance is positive and less than 1. System, multigrounded a system in which transformer neutrals and neutral conductors are directlygrounded, at frequent points along the circuit, with no intentional impedance added.System, ungrounded a system that is isolated, such as a delta, or grounded through an impedancegreater than that for an effectively grounded system.Tap a connection brought out from a winding at some point between its extremities to permitchanging of the turns ratio.Temperature class the maximum permissible winding temperature, and hence associatedtemperature rises, in C, that the insulation system is capable of sustaining for normal life (e.g., Class 105 C, Class 220 C, etc.).Total losses of a transformer the losses represented by the sum of the no-load losses and the load losses.Turns ratio of a transformer the ratio of the number of turns in the high-voltage winding to thatin the low-voltage winding.Note:In the case of a transformer that has taps for changing its voltage ratio, the turns ratio is based on the number ofturns corresponding to the principal tap of the windings to which operating and performance characteristics are referred. Two-winding transformer a transformer in which there are no coil turns that are common to bothprimary and secondary windings. 4Type Classifications 4.1 Standard types of transformers shall be recognized by three-letter designations according to the coolingcharacteristics outlined in Clauses 4.2 to 4.4. 4.2 The first letter designates the cooling medium surrounding the windings, as follows: a) A for air; or b) G for a gas other than air. 4.3 The second letter designates the method of circulating the cooling medium through the windings, asfollows: a) N for natural convection; or b) F for forced circulation. 4.4The third letter designates the manner of removing the heat from the cooling medium, as follows: a) N for natural circulation of outside air that is in contact with the windings (ventilated type); b) F for forced circulation of outside air that is in contact with the windings (ventilated type); c) C for natural convection to outside air that is not in contact with the windings (enclosed type); ord) P for forced circulation of outside air that is not in contact with the windings (enclosed type). 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Canadian Standards Association Dry-Type Transformers5October 20024.5Examples of designations under this classification system are as follows:a) ANN air-filled natural convection with open-ventilated enclosure through which the ambient airreadily enters and leaves the enclosure; b) GNC gas-filled unit cooled by natural convection of the gas within the enclosure and by naturalconvection of ambient air outside the enclosure; c) AFN air-filled cooled by forced circulation of the air within the open-ventilated enclosure and bynatural convection of ambient air outside the enclosure; d) GNP gas-filled unit cooled by natural convection of the gas within the enclosure and by forcedflow of ambient air over the outside of the enclosure; ande) ANC/ANP normal operation is air-filled, cooled by natural convection of the air within theenclosure and by natural convection of ambient air outside the enclosure, and emergency operationat higher kVCA rating is air-filled, cooled by natural convection of the air within the enclosure and byforced flow of ambient air over the outside of the enclosure. 5Mechanical Features 5.1Enclosures 5.1.1 Enclosures, if supplied, shall comply with Clauses 5.1.2 to 5.1.11. 5.1.2Enclosures shall be of noncombustible moisture-absorption-resistant material that shall enclose all liveparts except open connection terminals. 5.1.3The thickness of material used and the method of forming the enclosure shall be such that the enclosurewill withstand the stresses of handling, mounting, and such abuse to which it normally may be subjectedin service without reduction of internal spacings to live parts, loosening or displacement of parts, or otherdefects.Enclosures made from sheet steel shall be formed from stock that shall have a thickness not lessthan that specified in Table 1.Note:Turning the edge of the wall at least 90 for its full length is an accepted means of reinforcement.5.1.4Enclosures made of cast metal shall be not less than 3.2 mm in thickness, with the following exceptions: a)die-cast metal that has an area greater than 0.02 mor that has any dimension greater than 150 mm2shall not be less than 2.5 mm in thickness; and b) die-cast metal that has an area of 0.02 mor less or that has no dimension greater than 150 mm shall2be not less than 1.6 mm thick. 5.1.5Enclosures shall have the means to be securely mounted in a reliable manner, and the means ofmounting shall be such as to provide an air space of not less than 6.5 mm except at the point of supportbetween the enclosure and the surface on which it is mounted. 5.1.6Covers or removable portions of enclosures shall be secured in such a manner that the use of a tool is necessary in order to remove them. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association6October 20025.1.7If enclosures are provided with ventilating openings, the enclosure shall meet the followingrequirements: a) Ventilating openings, including perforated holes, louvres, and openings protected by means of wirescreening, expanded metal, or perforated covers, shall be of such size or shape as to prevent astraight circular rod, 13 mm in diameter, from touching live parts when inserted, except that if thedistance between live parts and the enclosure is greater than 100 mm, the test rod may be 19 mm indiameter.b) Openings shall have a minimum dimension of 10 mm to prevent clogging (e.g., with dust) exceptwhen filters or screens are provided, in which case instruction shall be provided regarding inspection,maintenance, and cleaning of the filters or screens.c) Openings in the top of an enclosure shall be suitably baffled to prevent foreign objects from fallinginto the enclosure and coming in contact with the windings and live parts.d) Openings in the bottom of an enclosure having provision for wall mountings shall be suitably baffledto prevent molten material from falling through.5.1.8Enclosures made of other than corrosion-resistant material shall be adequately protected against rustingby nonferrous coatings, by platings, or by painting. 5.1.9Enclosures for transformers intended for outdoor use shall comply with the requirements of CAN/CSA-C22.2 No. 94, except that if the enclosures will still pass the rain test, they may havea) multiple knockouts; and b) no overlap between the bottom cover and the enclosure. 5.1.10Wire Bending SpaceSufficient wire bending space shall be provided for the connection of the circuit conductors and shall benot less thana) the values specified in CSA C22.2 No. 0.12 for voltage ratings of 750 V and less; andb) a value sufficient to ensure that the conductors are not required to be bent at a radius less than seventimes the diameter of the cable for voltage ratings over 750 V.Note:To determine compliance with Clause 5.1.10, the bending radius should be that measured at the innermost surfaceof the cable.5.1.11Sprinklerproof EnclosuresEnclosures for transformers to be located in indoor areas where sprinklers are present shall comply withthe requirements of CSA C22.2 No. 47. 5.2Provisions for Lifting and Mounting 5.2.1Each transformer weighing more than 35 kg shall have provision for lifting and transformers above1500 kg shall, in addition, have provision for jacking and for moving by rolling or skidding. 5.2.2All transformers shall have provision for floor mounting. 5.3Terminal Arrangements 5.3.1Provision shall be made for one of the following methods of conductor entry: Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers7October 2002a) knockouts; b) potheads; c) junction boxes; d) bushings; e) clamping rings or other standard fittings; f) entry for bus bars or cable; or g) space for conduit entry by the customer. 5.3.2Terminals shall be marked to permit proper connection. 5.3.3Single-phase transformers having 120/240 V secondaries shall have a terminal arrangement suitable forseries-parallel connection. 5.3.4Terminals shall be of corrosion-resistant metal and shall be plated or otherwise made suitable for use withcopper and aluminum conductors.Their design shall take into account the cold-flow characteristics ofaluminum conductors. 5.4Spacings 5.4.1 Spacings through air between bare live parts of opposite polarity, and between bare live parts andnon-current-carrying metal parts, including cores and enclosures, shall be such as to successfully pass thedielectric tests specified in Clause 7.9 without breakdown. 5.4.2Minimum creepage distances over insulating surfaces of commonly used materials between terminalparts of opposite polarity, but not between bare live parts of opposite polarity or between bare live partsand non-current-carrying metal parts, shall be as specified in Table 2.5.4.3In the case of transformers that have windings in direct contact with ventilating air (see Clause 4.4), the arrangement of the core and coils shall be such that all ventilating ducts, ends of windings, andinsulating surfaces are accessible for cleaning with a vacuum cleaner, compressed air, or nitrogen. 5.5Grounding5.5.1A transformer intended to supply a circuit that is required by the Canadian Electrical Code, Part I, to begrounded shall be provided with a suitable means (e.g., a metal stud) inside the enclosure for connectingthe terminal pad of the neutral, the midpoint, or one end of the low-voltage winding to the core and tothe enclosure, if supplied.The stud shall be capable of accepting two connectors that are of suitable sizeto accept grounding conductors of the size specified in Table 3.One of the connectors shall be for thewinding ground and one for the enclosure ground in the event the transformer is connected using PVCconduit, armoured cable, or equivalent means.The stud shall be so located that a bare groundingconductor is unlikely to come in contact with bare live parts of the transformer.The terminal pad, whichis intended to be grounded, shall be provided with means for attaching the grounding connectors. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association8October 20025.5.2If a transformer is not intended for conduit connection to the supply, a provision for grounding (e.g., metal stud, ground pad, or lug) that is capable of accepting a grounding conductor of a sizespecified in Table 3 shall be made outside the enclosure. 5.5.3Cores, including core pressure plates, core clamps, and enclosures of transformers, shall be in goodelectrical contact with each other for the purpose of grounding. 6Marking 6.1GeneralEach transformer shall be plainly marked, in a permanent manner and in a place where the details can bemade readily visible after installation, with the following information: a) manufacturers name, trade name, or other recognized symbol of identification; b) serial, catalogue, style, model, or other identifying designation; c) type, in accordance with Clause 4; d) rated high and low voltages; e) tap voltages, if taps are provided, either as actual voltages or as a percentage of rated voltage; f) rated frequency; g) rated kVCA capacity; h) number of phases, unless this is clearly indicated on the connection diagram; i) per cent impedance at actual rated temperature based on 20 C ambient plus rated temperature risein degrees Celsius; j) rated temperature rise, in degrees Celsius; k) temperature class (from Table 4); l) weight; m) if the winding(s) are insulated for wye connection, they shall be so marked on the nameplate (forsingle-phase transformers only);n) a diagram, or equivalent information, for proper connection; o) a vector diagram for polyphase transformers; p) for enclosures other than General Purpose, the appropriate enclosure number type;q) for transformers having terminations, other than leads, that are suitable for copper or aluminumcable connections, the marking CU-AL; r) BIL (basic impulse level), where applicable;s) indication that the transformer is of the autotransformer type, if this is the case; andt) for harmonic content above 0.05 per unit, indication of the harmonic loss factor (F ) with theHLfollowing marking on the rating plate:Suitable for nonsinusoidal current load with Fnot toHLexceed __., where Fis defined by ANSI/IEEE C57.110 and may be 4, 9, 13, or a value calculatedHLfrom the harmonic current distribution.Alternatively, the K factor in accordance with CSA C22.2 No. 47 may be marked.If, due to space limitations, the marking is placed on a panel that is removed during installation ormaintenance, a second identification shall be provided inside the enclosure.6.2Identification of Windings6.2.1In general, the windings of a transformer shall be distinguished from one another as follows:a) Two-winding transformers shall have their windings designated as high voltage (HV or H) and lowvoltage (LV or X).b) Transformers with more than two windings shall have their windings designated as H, X, Y, and Z.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers9October 20026.2.2The sequence of designation shall be determined as follows:a) The highest voltage winding shall be designated as HV or H.b) The other windings shall be designated in order of decreasing voltage as X, Y, and Z.c) If two (or more) windings have the same voltage and different kVCA ratings, the higher kVCA windingshall receive a letter designation in accordance with the sequence by voltage specified in Item b).d) If two or more windings have the same kVCA and voltage rating, the designations of these windingsshall be arbitrarily assigned.6.3Marking of Terminals6.3.1External terminals shall be distinguished from one another by marking each terminal with a capital letterfollowed by a subscript number; for example, for a 3-phase 2-winding transformer, the terminals of the Hwinding would be marked H , H , Hand the terminals of the X winding would be marked X , X , X , etc.1 2 3 1 2 36.3.2The markings shall be so applied that if, for example, the phase sequence of voltage on the highestvoltage winding is in the time order H , H , H , it will be in the time order of X , X , Xand Y , Y , Y , etc.,1 2 3 1 2 3 1 2 3on the other windings.6.3.3A neutral terminal of a 3-phase transformer shall be marked with the appropriate letter followed by asubscript 0 (e.g., H , X , etc.).A neutral terminal common to two or more windings of a single- or0 03-phase transformer shall be marked with the combination of the appropriate winding letters, eachfollowed by the subscript 0 (e.g., H Xin the case of autotransformers).A terminal brought out from the0 0winding for some other use than that of a neutral terminal (e.g., a 50% starting tap) shall be marked as atap terminal.6.3.4If a transformer has a 2-terminal winding with one terminal grounded and the other ungrounded, thesubscript 2 terminal shall be the grounded terminal.7Electrical Features 7.1Temperature and Insulation 7.1.1 The five temperature classes shown in Table 4 shall be considered standard.The maximum permissibletemperature rise of the windings at rated voltage and kVCA output shall be as shown in Table 4. 7.1.2 Metallic parts in contact with or adjacent to the insulation shall not attain a temperature in excess of thetemperature class shown in the first column of Table 4. 7.1.3Exposed metallic parts shall not exceed a 65 C temperature rise. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.2 2 23 5 71I + I + I + ....Harmonic factor for current =IC9-02 Canadian Standards Association10October 20027.1.4 The maximum temperature, as measured on the insulation surface (during a full-load temperature teston the transformer), of factory-installed cable used for interconnections shall be limited to its recognizedtemperature rating. 7.1.5The temperature rise of bus bar when used as a coil lead or factory-installed interconnection (includingsuitably welded and bolted joints) shall be coordinated functionally with the insulation system of thetransformer.7.1.6Terminations used for field connections with cable and any point within the transformer enclosure that afield-installed cable might contact shall be limited to a 55 C temperature rise. 7.1.7The temperature rise of bus terminations for connection to a field-installed bus (including suitably boltedjoints) shall be coordinated functionally with the insulation system of the field-installed bus.7.1.8Transformers shall be capable of operating without exceeding the temperature rises specified inClause 7.1 and under the following conditions: a) in the case of transformers with primary taps delivering rated kVCA at rated output voltage, withprimary energized on lowest tap; b) for any tap delivering rated output kVCA at a lagging power factor of 80 or higher, with 5% aboverated output voltage;c) energized at 10% above rated output voltage at no-load; d) operating at an altitude not exceeding 1000 m; ande) having an approximately sinusoidal load current and a harmonic factor less than or equal to 0.05 perunit.When the harmonic factor for load current exceeds 0.05 per unit, the winding temperature rise shall bedetermined in accordance with the methodology of ANSI/IEEE C57.110. Notes:1)The harmonic factor for load current is the ratio of the effective value of all the harmonics to the effective value of thefundamental, calculated as follows:2)For operation of transformers at other than rated load or temperature rise or both, refer to ANSI/IEEE C57.96.3)For further information regarding harmonic loss factor, refer to ANSI/IEEE C57.110. Annex B of ANSI/IEEE C57.110provides a comparison of K factor and harmonic loss factor.7.2Kilovolt-Ampere Ratings 7.2.1Preferred self-cooled kilovolt-ampere capacities shall be as shown in Table 5.7.2.2Preferred forced-cooled ratings shall be 133% of self-cooled ratings.7.2.3Primary voltage taps shall be full-capacity taps and shall be two 2.5% taps above and two 2.5% tapsbelow rated voltage. Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. 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Canadian Standards Association Dry-Type Transformers11October 2002Where a transformer primary, because of relatively low voltage rating, has a volts-per-turn value thatdoes not permit tap steps of 2.5% (within 0.5% tolerance), it shall have, instead, a modified taparrangement as permitted by practical design considerations and as agreed to by the purchaser, whichshall be marked on the nameplate.(See Clause 8.4.3.)7.2.4Single- and 3-phase transformers larger than 10 kVCA and 15 kVCA, respectively, shall be provided withtaps as specified in Clause 7.2.3 unless otherwise specified by the purchaser. 7.2.5When connected on taps above or below rated voltage, the capacity shall be the full rated kVCA of thetransformer.7.3Voltage RatingsThe preferred voltage ratings shall be those shown in Table 6.7.4PolarityAll single-phase transformers shall have additive polarity unless otherwise specified by the purchaser.7.5Angular DisplacementAngular displacement of 3-phase transformers shall be in accordance with the diagram shown in Figure 1unless otherwise specified by the purchaser. 7.6Standard Percentage ImpedanceTransformers shall be designed to meet the minimum impedance levels as shown in Table 7 unlessotherwise specified.These impedance levels permit the use of minimum interrupting capacities of thesecondary main and branch circuit breakers.7.7Parallel OperationTransformers shall be considered suitable for parallel operation if their impedance comes within the limitsof Clause 8.4.7, provided that turns ratios and other controlling characteristics are suitable for suchoperation.7.8Audible Sound LevelsThe average sound level of the transformer shall not exceed the values specified in Table 8 unlessotherwise accepted by the purchaser.7.9Dielectric Withstand7.9.1GeneralThe neutral end of the windings or neutral terminals of a wye-connected transformer that is designed fora grounded wye connection may have an insulation level lower than that for line terminals.Such neutralends of windings and neutral terminals shall be connected to the transformer ground pad and systemground.7.9.2Applied Potential (Low Frequency)7.9.2.1A 60 Hz voltage not less than that specified in Table 9 or 10, as applicable, shall be applied betweeneach winding and the core for a period of 60 s.During this test all windings, except the one under test,shall be grounded to the core and enclosure.(For the neutral end of winding with graded insulation, see Clause 7.9.2.2.)Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association12October 20027.9.2.2The winding neutral with graded insulation described in Clause 7.9.1 shall have a minimum low-frequency test level of 4 kV for windings designed up to 1200 V, and 10 kV for windings designed above1200 V.7.9.3Induced PotentialAn ac voltage of twice the normal voltage of one winding shall be applied, at suitable frequency, for7200 cycles between the terminals of that winding with the ends of the other windings open.Fortransformers with graded insulation at the neutral as described in Clause 7.9.1, the voltage shall beapplied to another winding to develop twice the voltage between turns of the grounded winding.7.9.4Basic Impulse Insulation LevelThe transformer assembled in its own case, if supplied, shall be capable of withstanding impulse tests,both full wave and chopped wave, at the voltage levels shown in Table 9 or 10, as applicable.Fortransformers with graded insulation at the neutral as described in Clause 7.9.1, the neutral shall be testedfor 10 kV BIL for windings designed for voltages above 1200 V.When specified, the neutral shall bedesigned for a higher insulation level.7.9.5Single-Phase TransformersSingle-phase transformers with a voltage class of 2.5 kV and below shall be insulated for possible usewithin a 3-phase wye-connected bank.7.10Partial Discharges (Corona)7.10.1Transformers shall be designed to have a minimum partial-discharge extinction voltage of 110% of ratedwinding voltage when tested in accordance with Clause 8.3.5.7.10.2If partial-discharge inception does not occur at the intensity level specified in Table 11 when the windingvoltage is raised to 120% of the rated winding voltage, the transformer shall be considered to have metthe requirements of Clause 7.10.1.7.11Short-Circuit Capability under Fault Conditions7.11.1Transformers shall be capable of withstanding without damage the mechanical and thermal stressescaused by a short-circuit on the external terminals of any winding or windings, with rated voltagesmaintained across the terminals of all other windings intended for connection to sources of energy,provided thata) the magnitude of the rms symmetrical current in any winding of the transformer does not exceed25 times the rated current of the winding; andb) the duration of the short-circuit is limited to 2 s.7.11.2When specified, short-circuit tests shall be performed in accordance with IEEE C57.12.91 and shall haveshort-circuit characteristics in accordance with IEEE C57.12.01.7.11.3Certain transformers may have short-circuit currents that exceed those provided for in Clause 7.11.1,such as transformers with less than 4% impedance, certain multiwinding transformers, andautotransformers.It should be recognized that, although such cases do occur, the short-circuitLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.2( )2m 2mf s s(T ) e E e 1 1 = + + + =+ ssWtmC (T ) Canadian Standards Association Dry-Type Transformers13October 2002requirements for transformers built to this Standard are met if the transformers conform to the provisionsof Clause 7.11.1.When these conditions exist, provision should be made by the user to limit theshort-circuit to the values defined in Clause 7.11.1.7.11.4For determination of mechanical stress, the initial short-circuit current shall be assumed to be completelyoffset so as to give the maximum crest value of the short-circuit current.This maximum crest value ofthe short-circuit current is 2 times the crest value of the rms symmetrical short-circuit current decreasedby the decrement factor of the transformer winding.7.11.5The maximum crest value, I, of the short-circuit current that the transformer is required to withstandshall be determined as follows: I = KIsc whereK = [1 + (e) Sinn](n + B/2) R/Xwheree = 2.718n = arc tan X/R, in radiansR/X= ratio of effective alternating current ohms resistance to ohms reactance in the total impedance that limits the fault current for the transformer connections when the short-circuit occurs Isc =short-circuit current, rms, symmetrical7.11.6Care shall be exercised in the winding design and application of conductor material to limit the windingtemperature rise during a short-circuit condition to the limit provided for in Clause 7.11.1.The effect ofthe calculated temperature increase on a transformer shall be considered by the designer, and properallowance made in the design to meet this short-circuit current requirement.The method to be followedin calculating the temperature rise during such short-circuit shall be as given in Clause 7.11.7.7.11.7The winding temperature during a short-circuit shall be calculated on the basis of all heat stored in theconductor material and its associated turn insulation.The winding temperature will increase from 2 , thesstarting temperature, to 2during a specified time, t. 2shall be calculated using the following equation: f fwhere 2 = temperature in degrees Celsius of winding after t seconds short-circuit fT = 234.5 for copper= 225 for aluminum 2 = starting temperature in degrees Celsius equal tosa)30 C ambient temperature plus the measured hottest spot rise, if tested; or b)30 C ambient temperature plus the hottest spot winding rise shown in Table 4 e = 2.718whereW = short-circuit dc resistance conductor loss, at starting temperature 2 , in W/kg ofs sconductor materialt = time in seconds of short-circuit duration Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.AiC 401 243 for copperAc= +Ai970 794 for aluminumAc= +C9-02 Canadian Standards Association14October 2002whereAi= cross-sectional area of insulationAc= cross-sectional area of conductor E=per unit eddy current loss, based on resistance loss W, at the starting temperature 2s s8Tests8.1General8.1.1Where details in procedure, methods, precautions, and calculations in conducting tests are not specifiedherein, the requirements of IEEE C57.12.91 shall apply insofar as they are applicable.8.1.2Unless otherwise specified herein, all tests shall be carried out at normal ambient temperatures of 10 Cto 40 C.8.2Wave FormA sine-wave voltage shall be the standard, since the no-load loss and exciting current are affected by thewave shape of the impressed voltage.8.3Type Tests8.3.1GeneralThe following type tests shall be made:a) temperature rise; b) sound level; c) partial discharge (corona), except for windings of 1.2 kV and below; andd) basic insulation impulse level, except for windings of 1.2 kV and below.8.3.2SpecimensType tests shall be made on representative units to substantiate the ratings assigned to all other units ofbasically the same design, but these tests shall not be required when a record of a test made on a unit ofsimilar design, built in accordance with this Standard, can be furnished.Once made, the tests need notbe repeated unless the design is changed so as to modify performance under the specified type test.8.3.3Temperature Test 8.3.3.1 The limits of permissible temperature rise shall be as described in Clause 7.1.8.3.3.2Transformers shall be tested in accordance with IEEE C57.12.91.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers15October 20028.3.3.3Correction of temperature back to the moment of shutdown shall be made as described inIEEE C57.12.91.8.3.4Sound-Level TestThe average sound level of the transformer at no-load shall not exceed the levels specified in Table 8when tested in accordance with IEEE C57.12.91.8.3.5Partial Discharges (Corona) 8.3.5.1The minimum partial discharge extinction voltage shall be 110% of the rated winding voltage wheneach phase is tested in the circuit shown in Figure 3(a).The test shall be conducted first with one end ofthe winding under test grounded, and then (except in the case of windings that are intended to haveone end permanently grounded) with the other end grounded.8.3.5.2In cases where grounding one end of the high-voltage winding causes a problem in the measurement ofpartial discharges due to the 1.732 times normal voltage on the ungrounded terminal, the test circuits inthe following diagrams may be used, as applicable:a) Figure 3(b) for ungrounded single-phase transformers; b) Figure 3(c) for delta-connected transformers; and c) Figure 3(d) for wye-connected transformers with either isolated or grounded neutrals.8.3.5.3Each phase shall be calibrated and tested.For 3-phase transformers, the excitation shall be 3 phase.Thepartial discharge from each phase terminal may be measured in succession.8.3.5.4The test voltage shall be raised to 120% of the rated winding voltage and the inception voltage levelrecorded.Once the 120% level has been reached, the voltage shall be reduced and the extinctionvoltage level recorded.8.3.5.5The calibrating pulse generator shall meet the following requirements:a) A square wave pulse of known peak value shall be used for the calibrating procedure.The rise time ofthe pulse shall be less than 0.1 s, which approaches that of a typical partial discharge pulse.b) The pulse generator shall contain a peak-reading voltmeter to measure the peak voltage of theoutput pulse.Otherwise, separate accurate means, such as an oscilloscope, shall be provided.c) The internal impedance of the pulse generator shall be not more than 100 S to ensure against thecircuit loading having an adverse effect on the rise time.d) The output of the calibrating pulse generator shall be applied to the coupling impedance through a200 pF capacitor as shown in Figure 3(a).The circuit shall be arranged so that one terminal each ofthe pulse generator, the coupling impedance, and the oscilloscope are at ground potential.e) The sensitivity on the oscilloscope is calibrated for a signal of 20 pC (e.g., a 0.1 V peak-to-peak on the200 pF capacitor). 8.3.6Basic Impulse Insulation Level (BIL) 8.3.6.1Impulse TestsImpulse tests shall be applied to each line terminal.The following test shall be applied in order fromItem a) to Item c): Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association16October 2002a) one reduced full wave; b) two chopped waves; and c) one full wave.Impulse tests shall be performed according to IEEE C57.12.91.8.3.6.2Reduced Full Wave TestFor this test the applied voltage wave shall be 1.2 50 s and shall have a crest value of between 50 and70% of the full wave value given in Table 9 or 10, as applicable.8.3.6.3Chopped Wave TestFor this test the applied voltage wave shall be chopped by a suitable air gap.It shall have a crest valueand time to flashover in accordance with Table 9 or 10, as applicable.8.3.6.4Full Wave TestFor this test the applied voltage wave shall be 1.2 50 s and shall have a crest value in accordance withTable 9 or 10, as applicable. 8.3.6.5Failure Detection (See Annex C)Unless otherwise specified, ground-current oscillograms shall be the standard method of failuredetection, where applicable.Both ground-current oscillograms and voltage oscillograms may be usedfor failure detection.Any differences in the wave shape between the reduced full wave and the final fullwave that are detected by superimposing the two voltage oscillograms and that are not attributable toprotective devices or any such differences observed by comparing the chopped waves to each other maybe indications of failure.8.4Production Tests8.4.1GeneralThe following tests shall be applied as production tests on all transformers, except as indicated:a) voltage ratio; b) polarity or angular displacement; c) no-load losses and exciting current; d) load-loss and impedance voltage (to be applied on each production run but not necessarily eachindividual transformer unit); e) dielectric, applied and induced;f) resistance (for transformers above 500 kVCA only); andg) partial discharge (for cast-coil transformers only).Note:Items c), d), and f) do not apply to transformers rated 600 V and below and 500 kVCA and below unlessspecifically required by other standards.8.4.2Voltage RatioThe voltage ratio shall be determined for all taps as well as for the full winding.8.4.3Tolerance for Voltage RatioThe voltage ratio at no-load shall be within 0.5% of the nameplate marking, except that rated tapvoltages shall correspond to the voltage of the nearest turn if the voltage per turn exceeds 0.5% of thenameplate marking.8.4.4Tolerance for Losses and Exciting Current8.4.4.1Individual TransformersThe losses for individual transformers on a given order shall not exceed the guaranteed values by morethan 15% for no-load losses and exciting current, and 8% for total losses.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers17October 20028.4.4.2Average for Two or More TransformersThe average no-load losses, total losses, and exciting current for a given order of two or moretransformers shall not exceed the guarantees submitted.8.4.5Load Losses and Impedance VoltageThe load losses and the impedance voltage shall be determined for rated voltage, current, andfrequency, and shall be corrected to a reference temperature, which is defined as rated averagetemperature rise in degrees Celsius plus 20 C ambient.8.4.6Efficiency8.4.6.1The efficiency shall be determined from the sum of the load losses, corrected to actual rated temperaturebased on 20 C ambient plus rated temperature rise in degrees Celsius, and the no-load losses based onrated voltage, rated frequency, and unity power factor.8.4.6.2The tolerance for efficiency shall be in accordance with the tolerance for losses.8.4.7Tolerance for ImpedanceFor transformers within the scope of this Standard,a) the impedance of a two-winding transformer shall not vary from the guaranteed value by morethan 7.5%; b) the impedance of a transformer having three or more windings or having zig-zag windings shall notvary from the guaranteed value by more than 10%; c) the impedance of an autotransformer shall not vary from the guaranteed value by more than 10%; d) differences of impedance between two-winding transformers of the same design shall not exceed7.5% of the guaranteed values; e) differences of impedance between transformers of the same design having three or more windingsshall not exceed 10% of the guaranteed values; and f) differences of impedance between autotransformers of the same design shall not exceed 10% of theguaranteed values.8.4.8Regulation8.4.8.1The regulation shall be determined by calculation based on the measured values of the impedancevoltage and the losses, corrected to actual rated temperature based on 20 C ambient plus ratedtemperature rise in degrees Celsius.8.4.8.2The tolerance for regulation shall be in accordance with the tolerance for impedance and load losses.8.4.9Dielectric Tests8.4.9.1The standard dielectric test shall consist of the applied potential test and the induced potential test andmay be made at any convenient temperature. However, when a heat run is made, it shall be made whilethe transformer is still hot.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association18October 20028.4.9.2The applied potential test shall be made by applying a voltage at a frequency of 60 Hz from an externalsource, in accordance with the values given in Table 9 or 10, as applicable, and holding the voltageconstant for 1 min between each winding and the other windings and ground.The procedure given inIEEE C57.12.91 shall apply.8.4.9.3The induced potential test shall be made after the applied potential test by applying a voltage twice thenormal voltage of the winding between the terminals of one winding for 7200 cycles at a suitablefrequency, with the other windings open-circuited.8.4.9.4When an impulse test is performed, the induced and applied tests shall follow the impulse test.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit. Canadian Standards Association Dry-Type Transformers19October 2002Table 1Minimum Thickness of Sheet Steel Enclosures(See Clause 5.1.3.)Minimum thicknessWithout supporting frame orequivalent reinforcementWith supporting frame orequivalent reinforcementMaximum volume of enclosure, m3Maximum area ofany surface,m2Maximumdimension, mmmmMSGmmMSG0.0070.0210.0280.230.651.0Over 1.0 200 300 450 60010001500Over 15000.680.781.021.341.692.303.11222018161412100.680.780.781.341.341.341.3422202016161616Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association20October 2002Table 2Creepage Distance(See Clause 5.4.2.)Voltage class, kV When Table 9 applies When Table 10 appliesMinimum creepage distance, mm1.2 25 2.5 50 5.0 65 1008.7 100 13015.0 130 200*18.0 180* 250*25.0 250* 34.5 300* 46.0450* *This minimum distance may be reduced in practice subject to successful completion of dielectrictests prescribed in Table 9 or 10, whichever is applicable.Note:For transformer subcomponents of 0.250 kV class, creepage distance may be 15 mm.Table 3Minimum Size of Grounding Conductor(See Clauses 5.5.1 and 5.5.2.)Ampacity of largest secondary Minimum AWG size orconductor or equivalent forCross-sectionalequivalent coppermultiple conductors, A area, mm grounding conductor2100 or less8.367 8101125 13.30 6126165 21.15 4166200 26.67 3201260 33.62 2261355 53.49 0356475 67.43 00Over 475 85.01 000Note:The grounding conductor sizes are from Table 17 of the Canadian Electrical Code, Part I. 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Canadian Standards Association Dry-Type Transformers21October 2002Table 4Transformer Winding Insulation System(See Clauses 6.1, 7.1.1, 7.1.2, and 7.11.7.)Temperaturemeasured by rise ofspot rise, class, C resistance, C*CAverage winding riseWinding hottestClass 130 75 90Class 150 90 110Class 180 115 140Class 200 130 160Class 220 150 180*Higher average winding temperature rises by resistance may be permitted if themanufacturer provides thermal-design test data acceptable to the purchasersubstantiating that the temperature limits of the insulation are not exceeded.Note:The average winding rise and hottest spot are based on an average dailyambient temperature of 30 C with a maximum ambient temperature of 40 C at analtitude not exceeding 1000 m.Table 5Standard kVCA Ratings for Dry-Type Transformers(See Clause 7.2.1.)Single-phase ratings3-phase ratings 2 63 95 1510 3015 4525 7537 11250 15075 225100 300167 450250 500333 750500 1000667 1500833 20001000 25001250 30001667 37502500 50003333 75005000 open-endedopen-endedLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association22October 2002Table 6Preferred Voltage Ratings(See Clause 7.3.)Preferred primaryPreferred secondaryvoltage ratings voltage ratingsSingle-phase 3-phase Single-phase3-phase transformers transformers transformers transformers120/240480 120/240 208Y/120 480600 240/480 480Y/2772 400 2 400480 600Y/3474 160 4 160600 4160Y/24007 200 12 47024008 000 13 860416012 470 24 94013 860 27 60014 400 34 50016 000 46 00020 00024 94034 50046 000Notes: 1)If a 3-phase transformer is to be applied in a wye-wye configuration, the supplier shall beso advised at the time of ordering. 2)If a 3-phase transformer is manufactured for application in a wye-delta configuration,the supplier shall include a precautionary note on the transformer: DO NOT CONNECTPRIMARY SIDE NEUTRAL TO SYSTEM NEUTRAL OR TO GROUND. 3)Single-phase transformers with a voltage class of 2.5 kV and below shall be insulated for possible use within a 3-phase wye-connected bank.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers23October 2002Table 7Impedance Levels(See Clause 7.6.)Base kVCA %Minimum transformer impedance, 0150 Manufacturers standard151300 4301600 56012500 625015000 6.550017500 7.5750110 000 8.5Above 10 000 9.5Notes: 1)Normal impedance tolerance values in accordance withClause 8.4.7 apply to values in this Table (i.e., for 300 kVAtransformers, 3.75% tested impedance is acceptable as it is within7.5% tolerance of 4% impedance).2)For frequencies other than 60 Hz, the impedance valuesmaybe given special consideration by the manufacturer andpurchaser.3)With proper system protection and coordination, thepurchaser may specify lower impedance. 4)This Tableis not applicable to autotransformers.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association24October 2002Table 8Average Audible Sound Level, dB(A)(See Clauses 7.8 and 8.3.4.)Self-cooled ventilated voltage Self-cooledline-to-line sealedPhase kVCA 1.2 kV up to 15 kV up to 25 kV Up to 15 kVEquivalent2-winding, Up toAbove 1.2 kVAbove 15 kV Single09 45 50 54 45phase 1050 50 55 59 5051100 55 60 64 55101167 60 65 69 57168333 65 68 72 593341000 68 68 72 61Three 09 40 45 49 45phase 1050 45 50 54 5051150 50 55 58 55151300 55 58 61 57301500 60 60 63 59501700 62 62 65 617011000 64 64 67 6310011500 65 65 68 6415012000 66 66 69 6520013000 68 68 71 6630013750 71 71 74 6837515000 73 73 76 70Notes:1)The above values apply only to specified test conditions.The character and location of surroundingsurfaces and mounting and installation constructional features may cause sound levels at the installation todiffer considerably from these values.2)The audible sound level values specified in this Table are the average of the readings taken on onetransformer from various points around the transformer enclosure.3)Audible sound levels of transformers rated above 25 kV (125 kV BIL) shall be a matter for specialconsideration.The manufacturer should be consulted regarding sound levels on such units.4)Audible sound levels of transformers with kVCA ratings above those listed shall be a matter for specialconsideration.The manufacturer should be consulted regarding sound levels on such units.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers25October 2002Table 9Insulation Voltage Classes and Dielectric Tests for Dry-Type Transformers*(See Clauses 7.9.2.1, 7.9.4, 8.3.6.28.3.6.4, 8.4.9.2, B.2.2.1, B.2.2.2.2, and Table 2.)Insulation Applied potential BIL full- and Chopped-wavevoltage class, Nominal transformer (low frequency) chopped-waveminimum time tokV voltage test, kV kV crest flashover, s 1.2 1 200 and less 4 2.5 2 400 10 20 1.05.0 4 160Y/2 40012 30 1.04 1604 8008.7 8 320Y/4 80019 45 1.257 2008 32015.0 12 470Y/7 200 31 60 1.513 860Y/8 00012 47013 86018.0 24 940 GrdY/14 400 34 95 1.627 600 GrdY/16 00025 34 500 GrdY/19 900 40 125 2.024 940Y/14 40024 94027 600Y/16 00027 60034.5 34 500 50 150 2.2534 500Y/19 90046 000 GrdY/26 60046 46 000 65 200 3.0*Where higher test voltage levels are required, refer to Table 10.Notes:1)A single voltage of 4160 represents a delta-connected 3-phase transformer for connection to a 3-wire system or asingle-phase transformer for connection to a 2-wire ungrounded system.A voltage such as 4160 GrdY/2400 represents awye-connected 3-phase transformer having an effectively grounded neutral for connection to a 4-wire multigroundedsystem.It also represents a 2400 V single-phase transformer with an effectively grounded neutral end in the 2400 Vwinding.It may be connected line-to-ground or as part of a 3-phase bank on a 4160 V 4-wire multigrounded system.Avoltage such as 4160Y/2400 represents a 3-phase transformer with a fully insulated neutral for connection to a 4160 V4-wire system.For further details, refer to IEEE C57.12.01, Figure 2.2)Low-frequency test levels are for application to windings that do not have reduced neutral terminal insulation.(See Clause 7.9.2.2 for windings that are grounded Y.)3)If there is any possibility that the transformer terminals will be subjected to transient overvoltages exceeding 80% oftheir BIL, it is recommended that they be protected with appropriate surge arresters (see Annex B). 4)Equipment having a voltage rating between listed values shall be tested at the higher level.5)A user requiring a higher-than-rated BIL for some specific situation may specify the higher BIL rating.In such a case,the applied potential test shall be in accordance with that specified for the insulation voltage class unless otherwisespecified.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association26October 2002Table 10Insulation Voltage Classes and Dielectric Test for Dry-Type Transformers that Fully Coordinate with Metal-Clad Switchgear or for Other Special Requirements(See Clauses 7.9.2.1, 7.9.4, 8.3.6.28.3.6.4, 8.4.9.2, B.2.2.1,B.2.2.2.2, and Tables 2 and 9.)Insulation Applied potential BIL full- and Chopped-wavevoltage class,Nominal transformer (low frequency)chopped-waveminimum time tokV voltage test, kV kV crest flashover, s 5.0 4 160Y/2 40019 60 1.04 1604 8008.7 8 320Y/4 80026 75 1.257 2008 32015.0 12 470Y/7 200 34 95 1.513 860Y/8 00012 47013 86018.0 24 940 GrdY/14 400 50 110 1.627 600 GrdY/16 000Notes:1)A single voltage of 4160 represents a delta-connected 3-phase transformer for connection to a 3-wire system or asingle-phase transformer for connection to a 2-wire ungrounded system.A voltage such as 4160 GrdY/2400 represents awye-connected 3-phase transformer having an effectively grounded neutral for connection to a 4-wire multigroundedsystem.It also represents a 2400 V single-phase transformer with an effectively grounded neutral end in the 2400 Vwinding.It may be connected line-to-ground or as part of a 3-phase bank on a 4160 V 4-wire multigrounded system.Avoltage such as 4160Y/2400 represents a 3-phase transformer with a fully insulated neutral for connection to a 4160 V4-wire system.For further details, refer to IEEE C57.12.01, Figure 2.2)Low-frequency test levels are for application to windings that do not have reduced neutral terminal insulation.(See Clause 7.9.2.2 for windings that are grounded Y.)3)If there is any possibility that the transformer terminals will be subjected to transient overvoltages exceeding 80% oftheir BIL, it is recommended that they be protected with appropriate surge arresters (see Annex B). 4)Equipment having a voltage rating between listed values shall be tested at the higher level.5)A user requiring a higher-than-rated BIL for some specific situation may specify the higher BIL rating.In such a case,the applied potential test shall be in accordance with that specified for the insulation voltage class unless otherwisespecified.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit. Canadian Standards Association Dry-Type Transformers27October 2002Table 11Partial-Discharge Pulse Intensity(See Clause 7.10.2.)VoltagePartial-discharge pulseclass,intensity (in the transformerkV winding only), pC1.2 502.5 1005.0 1008.7 10015 10025 15034.5 15046 in accordance with anagreement between purchaserand manufacturerLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.H2H3H1H2H3H1H2H3H1X2X3X1X2X3X1X2X3X1H2H3H1X2X3X1Angular Displacement 0Angular Displacement 30H1Connect MeasureH2X1X2H1ConnectH2X1X2X3X4MeasureC9-02 Canadian Standards Association28October 2002Figure 1Angular Displacement(See Clauses 3 and 7.5.)Figure 2Polarity(See Clause 3.)Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.Cal. cap. 200 pFLegend:C = Coupling capacitor1000 pF minimumZ = Impedanceg = Protective gapCC(c)CCZCZC(d)ZCZZCZCZZgZVScopeTo scopeTo scopeNote:The value of Z shall be selected to provide proper impedance matching for the test equipment being used. The coupling capacitors shall be as closely matched as possible.To scopeTo scopeTo scope To scopeTo scope To scopeCalib.gen.(a)(b)HVHVHVLVTestpieceExcitationvoltagesupplyHV Canadian Standards Association Dry-Type Transformers29October 2002Figure 3Test Circuits for Partial-Discharge Test Circuit(See Clauses 8.3.5.1, 8.3.5.2, and 8.3.5.5.)Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association30October 2002Annex A (informative)Guideline for Application, Installation, andMaintenance of Dry-Type TransformersNote:This Annex is not a mandatory part of this Standard.A.1Selection of TransformerA.1.1GeneralThe transformer should be selected with due regard toa) connected load currents and possible short-time overload currents of the circuit, including sustainedharmonics when the harmonic factor (defined in Clause 7.1.8) exceeds 0.05 per unit; b) repetitive transient currents of the circuit, such as transformer-magnetizing inrush current, motor-starting current and capacitor inrush current;c) coordination with other circuit components and protective devices; d) life expectancy and maintenance requirements of auxiliary equipment such as fans and controls; ande) multiple thermal ratings.A.1.2Non-sinusoidal Load CurrentsWhen a transformer supplies non-sinusoidal load currents with a harmonic factor (defined in Clause7.1.8) exceeding 0.05 per unit, harmonic currents are generated that may cause excessive losses andabnormal heating.Refer to ANSI/IEEE C57.110 for further guidance.A.2Unusual Temperature, Altitude, and EnvironmentalService ConditionsA.2.1Higher or Lower Ambient TemperaturesEquipment may be used at higher or lower ambient temperatures than those specified in Clause 7.1.1,but its performance may be affected and consideration should be given to these applications.SeeANSI/IEEE C57.96 for rerating factors that can be applied to transformers operated at higher or lowerambient temperatures.A.2.2Applications at Altitudes Greater Than 1000 mA.2.2.1GeneralDry-type transformers, since they depend upon air for their insulating and cooling medium, will have ahigher temperature rise and a lower withstand voltage when operated at altitudes above 1000 m.A.2.2.2TemperatureDry-type transformers designed for a temperature rise in accordance with Clause 7.1.1 may be operatedat rated kVCA at altitudes greater than 1000 m without exceeding the temperature limits, provided thatthe 24 h average ambient temperature does not exceed the temperature outlined in ANSI/IEEE C57.96for the applicable altitude.A.2.2.3InsulationThe dielectric strength of dry-type transformers decreases as the altitude increases due to the effect ofdecreased air density.ANSI/IEEE C57.110 shows the approximate relative dielectric strength for altitudesabove 1000 m.The dielectric strength at higher altitudes may be found by multiplying the dielectricstrength at 1000 m by the correction factor for the respective altitude.The manufacturer should beLicensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers31October 2002informed when transformers are to be installed at altitudes above 1000 m so that appropriate airclearances for the altitude will be provided during design.A.2.2.4Load Derating FactorsTo ensure temperature limits are not exceeded where the transformer is operated in a 30 C ambient ataltitudes in excess of 1000 m, the load on the transformer should be reduced in accordance withANSI/IEEE C57.96.A.2.3Environmental ConditionsOther unusual environmental conditions that may affect design and application can exist and are notnecessarily covered by this Standard.These conditions should be brought to the attention of thoseresponsible for the design and application of the equipment.Examples of such conditions area) damaging fumes and vapours, excessive and abrasive dust, steam, salt spray, excessive moisture anddripping water, etc.; b) abnormal vibration, shocks, and tilting; c) excessively high and low temperatures; d) unusual transportation and storage conditions; e) unusual space limitations; f) difficulty of maintenance, poor waveform, unbalanced voltage or unusual operating duty, frequencyof operation, insulation requirements, etc.; andg) areas that may contain hazardous materials in sufficient quantity to cause an explosion.A.3General Precautions during InstallationA.3.1ShippingThe transformer should be inspected to ensure that it has not been damaged in shipment.A.3.2InstructionsHookup instructions and other installation instructions furnished with the transformer should be checked. Examples are instructions relating toa) the method of lifting; b) the removal of bolts or packing material used in shipment only; c) for wall-mounted transformers, mounting bolts of sufficient size; d) the temperature rating of lead insulation required; e) the voltage rating of transformer and actual voltage of the line to which it is going to be connected,and the connection of primary leads and/or taps as required for that voltage; andf) the output voltage after installation. A.3.3SoundAudible sound may be a factor, and consideration should be given to the specific location and method ofinstallation of the transformer, keeping in mind the following recommendations:a) mount the transformer away from corners of walls or ceilings; b) provide a solid foundation for mounting and then use vibration-dampening mounts if not alreadyprovided in the transformer; c) provide flexible conduit to make the connection to the transformer; d) use sound-absorbing material on the walls and ceiling; and e) locate the transformer as far as is practicable from areas where high sound levels are undesirable.A.3.4LocationFactors that should be kept clearly in mind when locating dry-type transformers are accessibility,ventilation, atmospheric conditions, spacings, and sound.See also Section 26 of the Canadian ElectricalCode, Part I, on dry-core transformers.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. 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Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association32October 2002A.3.5VentilationA.3.5.1Adequate ventilation is essential for the proper cooling of dry-type transformers and associatedswitchgear, and clean air is desirable.If a location presents a particular problem, a source of filtered airmay reduce the problem.A.3.5.2When transformers are installed in vaults, stairwells, closets, and other restricted spaces, sufficientventilation should be provided to hold the air temperature within established ambient limits whenmeasured near the transformer air inlets.It is important that a maximum ambient of 40 C (average30 C over 24 h) not be exceeded unless a transformer to suit a higher ambient is specified or a deratingfactor is applied.(See ANSI/IEEE C57.96 for derating factors.)Maintaining the ambient so that themaximum of 40 C is not exceeded usually requires approximately 3 mof air per min per kilowatt of3transformer loss.A.3.5.3For each 100 kVCA of transformer rating, total inlet and outlet opening may be required to have a netarea of at least 0.1 m .The actual area of ventilated openings required depends on the configuration of2the space, the location of openings, and the maximum loads to be carried by the transformers.A.3.5.4The ventilating screens and openings in the transformers are designed to provide adequate ventilationfor the transformer and should not be restricted in any way.The ventilating screens and openings in thetransformers are designed to prevent entrance of most small animals and foreign objects.However, insome locations, it may be necessary to consider additional protection in consultation with themanufacturer.A.3.6Atmospheric ConditionsA.3.6.1Exposed core and ventilated dry-type transformers are normally designed for installation indoors in drylocations.When it is recommended by the manufacturer, they may be installed outdoors if they aresuitably protected or if they are of outdoor construction.They will operate successfully where thehumidity is high, provided that precautions are taken to keep them dry if they are shut down forappreciable periods.A.3.6.2Locations where there is dripping water should be avoided or suitable protection should be provided toprevent water from entering the enclosure.Precautions should be taken to guard against the accidentalentrance of water from a)an open window, skylight, or other opening; b)a break in a water or steam line; c)flooding; or d)the use of water near the transformer.Transformers should be installed in locations where the ambient atmosphere is free from unusualchemical fumes or excessive dust.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers33October 2002A.4MaintenanceA.4.1Dry-type transformers require occasional external cleaning, repainting, internal cleaning of air ducts, etc.,and periodic inspection.Where periodic inspection cannot be made, it should be recognized that the lifeof the transformer may be affected.A.4.2The frequency of inspection depends on the atmospheric and/or environmental conditions at a giventransformer installation or location.A transformer may operate satisfactorily for many years withoutattention but, under unusual service conditions, maintenance may be required in a matter of months.A.4.3If it is known that a transformer has been subjected to heavy short-circuit current stresses, special effortsshould be made to inspect it at the earliest possible opportunity, since the ability of the transformer tocarry rated load current or fault current may be seriously impaired if the windings have shifted.A.4.4 Some maintenance may be conducted while the transformer is energized.This would include peripheralinspection, external dust removal, external painting of enclosed units when no exposed electrical wiringor terminations exist, recording of service data, etc.A.4.5 Other maintenance is performed with the transformer in a de-energized condition.This would includetap changing, internal inspection and cleaning, locating causes of faulty performance, replacing parts,internal painting, etc.Corrective maintenance should be performed by a qualified person who is familiarwith the construction and operation of the apparatus and the hazards involved.In conducting correctivemaintenance, such a person shoulda) be sure that the transformer is disconnected from all electrical power sources before servicing (liveparts with a potential exceeding 30 volts-to-ground are considered to present a shock hazard); b) after power has been disconnected from the transformer, attach ground leads or their equivalent tothe input and output terminations of the transformer.Such grounding may be unnecessary in thecase of low-voltage transformers that can be visibly isolated from energized conductors by otherdisconnecting means; c) inspect insulators, terminals, and terminal boards for discharge (tracking), breaks, cracks, or burns. Where abnormal conditions such as salt deposits, dust, or acid fumes prevail, the insulators should becleaned.This is necessary to avoid flashover as a result of the accumulation of foreign substances ontheir surface; d) inspect terminals for alignment, tightness, pressure, burns, or corrosion.Pitted or badly burnedterminals should be replaced.If pitting or burning is of a minor nature and any plating is notdamaged, the surface should be smoothed down with clean, fine sandpaper (not emery), or themanufacturers recommendations should be followed; e) inspect for moisture conditions that may cause corrosion or harmful lowering of insulation levels; f) inspect air ducts for the accumulation of dust and foreign substances; if necessary, remove theaccumulation; g) see that bolts, nuts, washers, pins, and terminal connectors, including the ground connection, are inplace and in good condition; h) periodically inspect ground connections and ground contact surfaces for looseness of connections,erosion, corrosion, and/or other conditions detrimental to a good low-impedance andcurrent-carrying connection; andi) check insulated joints for localized heating and the condition of the insulation around the joints. When localized joint heating is present, the joint should be reconstituted and reinsulated.Any notedinsulation deterioration should be cause for reinsulating the joint. Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.C9-02 Canadian Standards Association34October 2002Annex B (informative)Guideline for Overvoltage and OvercurrentProtection of Dry-Type Transformers Note:This Annex is not a mandatory part of this Standard.B.1Overcurrent Protection A transformer can be protected from the effects of high short-circuit currents by the use of overcurrentprotective devices.(See Section 26 of the Canadian Electrical Code, Part I, for overcurrent protectionrequirements.) B.2Overvoltage Protection B.2.1Transformers are designed to operate at 5% overvoltage at rated load and 10% overvoltage at no-load(see Clause 7.1.8).They are not designed to operate when subjected to sustained overvoltage such asthat which occurs under ferroresonant conditions.If single-pole switching is planned for units of 15 kVclass or above, with ungrounded primaries, the problems of ferroresonance should be considered. B.2.2Surge Voltage Protection B.2.2.1When transformers are subject to surge voltages of more than the kV crest (shown in the fourth columnof Tables 9 and 10) divided by 1.2, they should be protected by surge arresters at the transformerterminals that will limit the surge to the above value or less at the transformer terminals. Note:Surge arresters should be installed within 3 circuit metres of the transformer terminals if it is not practicable toinstall them at the transformer terminals. B.2.2.2Choice of Surge Arrester B.2.2.2.1Calculation of the voltage rating of the surge arrester to be selected is shown in Table B.1.B.2.2.2.2Select an arrester with a voltage rating calculated according to Table B.1 with a front-of-wave crestsparkover voltage or a crest voltage corresponding to a 5 kA discharge (whichever is greater), less than the crest voltage of chopped-wave BIL shown in the fourth column of Table 9 or 10, as applicable, divided by 1.2.Table B.1Voltage Ratings of Surge Arresters(See Clauses B.2.2.2.1 and B.2.2.2.2.)Circuit surge arrester, kV Voltage rating of applied Ungrounded 1.08 10 system voltage* Effectively grounded 0.80 10 system voltage*Multigrounded 0.72 10 system voltage* 333*This voltage is the nominal system line-to-line voltage (see CSA CAN3-C235).Note:If the calculated kV value falls between two standard surge arrestervoltage ratings, use the higher rating. Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. 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Canadian Standards Association Dry-Type Transformers35October 2002Annex C (informative)Guideline for Interpretation of Voltage andCurrent OscillogramsNote:This Annex is not a mandatory part of this Standard.C.1GeneralInterpretation of oscillograms is a task requiring skill.It is often difficult to decide the significance ofdiscrepancies because of the large number of possible disturbance sources.Useful criteria of satisfactory trace superimposition can be found in ANSI/IEEE C57.98.C.2Ground-Current OscillogramsAny differences in the wave shape between the reduced full-wave and the final full-wave currentoscillograms may be indications of failure or deviations due to noninjurious causes.They should be investigated fully and explained by a new reduced wave and full wave test.In air- or gas-insulated apparatus, partial discharges may produce high-frequency oscillations on thewave.This is not an indication of failure and should be taken into account in interpreting the traces.C.3Voltage OscillogramsAny unexplained differences between the reduced full wave and the final full wave are indications offailures.Explainable deviations such as those caused by conditions external to the test circuits or partialdischarges in air- or gas-insulated apparatus are not indications of failure and should be taken intoaccount in interpreting the traces.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010. Single user license only. Storage, distribution or use on network prohibited./Permis d'utilisateur simple seulement. Le stockage, la distribution ou l'utilisation sur le rseau est interdit.Pro