CAN/GSA - C88-M90 (Reaffirmed 1994) Power Transformers and
Reactors Electrical Power Systems and Equipment A National Standard
of Canada Licensed for/Autoris Lawrence Duong, Sold by/vendu par
CSA on/le 3/25/2010. Single user license only. Storage,
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le rseau est interdit.(Reaffirmed 2009)The Canadian Standards
Association (CSA), under whose auspices thisNational Standard has
been pro- duced, wascharteredin1919and accredited by the Standards
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CSA standards reflect a national consensusof produc- ers and users
including manufacturers,consumers, retailers, unionsand
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are used widely by industry and commerce and often adoptedby mu-
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further informationon CSA services,write to Canadian Standards
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M9W 1R3 The Standards Council of Canada is the coordinat- ing body
of the NationalStandards system, a federation of independent,
autonomous organizations working to- wardsthe further development
and improvement of voluntary standardizationin the national
interest. The principal objects of the Council are to foster and
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provide to the greatest practicable extent a balance of
representation of producers, users, consumers, and others with
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Those who have a need to apply standards are encour- aged to use
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6N7 National Standards of Canada are available in English or in
French 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.General Instruction No. 2 CAN/GSA-C88-M90 November1990 CSA
Standard CAN/CSA-C88-M90,Power Transformers and Reactors,was
published in August 1990;it consisted of 91 pages, each of which
was dated August 1990. Errata to Tabte 2 and Figures 4, 5, and 6
have been incorporated (and identified by a vertical line in the
margin) in the attached replacement pages. CSA Standard
CAN/CSA-C88-M90now consists of the following pages: 332,3576,7982,
8591dated August 1990; 33, 34, 77, 78, 83, and 84 dated
November1990. These replacement pages are to be inserted into your
copy of the Standard; the pages replaced shouldbe kept for
reference. 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.Note:In forced-directed flow, the
oilisdirected from the coolers into the inletducts of all or some
windings of the transformer, so as to pump the oil through the
windings. 6.4 Designations and Order of Symbols The designations
and order of symbols shall be as shown in Table 1. Table 1
Designations and Order of Symbols 1st Letter2nd Letter3rd Letter4th
Letter Internal coolingType of internalExternal coolingType of
external mediumcirculationmediumcirculation 6.5Standard Type
Designations The standard types of transformers with their
designations shall be asfollows: Standard Type Designation (a)
Oilfilled natural cooling ONAN; (b) Oilfilled water cooling ONWF;
(c) Oilfilled forcedair cooling ONAF; (d) Oilfilled forcedoil water
cooling OFWF; (e) Oilfilled forcedoil forced-air cooling OFAF; (f)
Oilfilled forceddirected oil forcedair coolingODAF; (g) Oilfilled
forcedoil natural cooling OFAN; (h) Flameretardant liquidfilled
natural cooling LNAN; (i) Flameretardant liquidfilled water cooling
LNWF; (j) Flameretardant liquidfilled forcedair cooling LNAF; (k)
Flameretardant liquidfilled forcedliquid water cooling LFWF; (1)
Flameretardant liquidfilled forcedliquid forcedair cooling LFAF;
(m) Flameretardant liquidfilled forcedliquid natural cooling LFAN.
6.6 Type Designation for More Than One Method of Cooling Where the
apparatus has more than one method of cooling, the type
designations for all methods shallbe stated, separated from each
other by an oblique (/). In all cases of multiple cooling, the
power for each stage of cooling shall be designated. Note: Typical
examples are (a)ONAN/ONAF 30/40 MVA--an oil-filled transformer
having a naturally cooled (ONAN) rating of 30 MV'A and a
forced-air-cooled (ONAF) rating of 40 MVA; (b)ONAN/ONAF/ONAF
30/40/50 MV'A--a transformer having a naturally cooled (ONAN)
rating of 30 MV'A, a forced-air-cooled (ONAF)rating of 40MVA
achieved by operating only part of the fans, and an increased
forcedair-cooled (ONAF) rating of 50 MV'A when allthe fans are
operating; (c)ONAN/ONAF/OFAF 30/40/50 MVA--a transformer having a
naturally cooled (ONAN) rating of 30 MV'A, a
forced-air-cooled(ONAF) rating CAN/CSAC88M90 - November1990 Page 33
(Replaces p.33,August 1990) Licensed for/Autoris Lawrence Duong,
Sold by/vendu par CSA on/le 3/25/2010. Single user license only.
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d'utilisateur simple seulement. Le stockage, la distribution ou
l'utilisation sur le rseau est interdit.of 40 MV'A with only the
fansoperating, and aforced-oil forced- air-cooled (OFAF) rating of
50 MVA with both fans and oil pumps operating; and
(d)ONAN/ONAF/ODAF 30/40/50 MV'A--a transformer having a naturally
cooled (ONAN) rating of 30 MVA, a forced-air-cooled (ONAF) rating
of 40 MVA with only the fans operating, and aforceddirected oil-
forced-air-cooled (ODAF) rating of 50 MVA with bothfans and pumps
operating. For ODAF theinstruction bookfor the transformer
shallidentify windings with and without forceddirected flow
cooling. 7.Ratings 7.1Preferred MVA Ratings The preferred MVA
ratings are stated in Table 2 for singlephase and threephase
twowinding transformers, multiwinding and auto transformers when
only two setsof terminals are brought out of the tank, and
shuntreactors (for basis of Mvar rating see Clause 20.1). Table 2
Preferred MV'A Ratings for Transformers Preferred ratings in MVA
0.5550500 0.676.6766.7667 0.838.3383.3833 110100 1.2512.5125
Singlephase 1.6716.7167 220 200 2.525250 3.3333.3333 440400
1.5151501500 2202002000 2.525250 330300 3.7537.5375 Threephase 5 6
7.5 10 12 50 60 75 100 120 500 600 750 1000 1200 Note:For
multiple-rated transformers, the preferred MVA rating for the ONAN
rating is according to Table 2; for the first stage of forced
cooling (ONAF)the preferred increase is 33, and for the second
stage of forced cooling (ONAF/ONAF or OFAF)the preferred
CAN/CSAC88-M90 - November1990 - Page 34 (Replaces p. 34, August
1990)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.Type (B) Series Winding in Input (Constant Load Voltage
LTC Compensates for Varying Source Voltage) Notes: (1) A booster
transformer may be used where the linecurrent exceeds theload
tapchanger capability. (2) 10% voltage regulation is shown in this
example. (3)Arrangements shown are for singlephase transformers.
Figure 4 Voltage LimitsSeriesVoltage Regulators CAN/CSAC88-M90 -
November1990 - Page 77 (Replacesp.77, August 1990) SourceLoadSource
VoltageVoltageVoltage Load Vollage 120% Maximum Raise Variationwith
Positionof Load-Tap Changer MaximumLower Source Source p Fixed turn
windingSeries winding Load 4--o Type(A) Series Winding in Output
(Constant Source Voltage LTC Varies Load Voltage) Series winding
Load Fixed turn winding Licensed for/Autoris Lawrence Duong, Sold
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d'utilisateur simple seulement. Le stockage, la distribution ou
l'utilisation sur le rseau est interdit.22.7 Rating Plate
Regulators shallbe provided with rating plates in accordance with
Clause 17, except that (a) the rated nominal input and
outputvoltages shall be shown for at leastthosetapchanger positions
that represent the minimum, neutral,and maximum voltages; (b) the
rated input and output currents shallbe shownfor all voltage
positions as required in Clause 22.7(a); and (c)impedance voltages
shallbe shownfor the positions required by Clause 22.7(a)(see
Clause 22.4.4). 22.8Mechanical Features and Accessories
22.8.1Standard Mechanical Features and Accessories The standard
mechanical features and accessories listedin Clause 15.1,with the
following additions, shallbe standard and supplied with the
regulator: (a) A driving motor shall be supplied for operating the
LTC switch.If singlephase, it shallbe without centrifugal switch.
(b) A handcrank or handwheel for manual operation ofthe driving
mechanism shall be supplied. If a handcrank or spoketype of
handwheel is provided, it shallbe interlocked to prevent operation
by the motor while the crank or spoketype hand-wheel is engaged. A
place for storing the handcrank or handwheel, if detachable,
shallbe provided. (c)Mechanically operated electric limitswitches
and mechanical stops shallbe provided on the drive mechanism to
prevent travel beyond the extreme LTC switch positions. (d) A
positionindicating device with drag handsshallbe supplied.
Thisindicator shall be labelled, with 0 as the neutral position.Tap
positions that give a progressively lowerload voltage
(sourcevoltage being considered fixed) shallbe labelled as
1L,2L,3L, etc. Tap positions that give a progressively raised load
voltage (source voltage being considered fixed) shall be labelled
as1R,2R,3R, etc.If several positions correspond to the same load
voltage orturnsratio,they shallbe noted by the numberletter
combination but followed by A,B,C, etc (eg, a tap changer with
three neutral positions shallbe labelled OA,OB, OC). For automatic
or manual operation, the control system shallbe such that the tap
changer shall stop on only one of these positions. (e) A local
control switch and provision for adding a remote control switch
shall be supplied. (f) Means of filling, draining, venting, and
liquid level indication shall be supplied foreach separate liquid
chamber. Liquiddrain valve for diverter shallbe supplied when
applicable. (g) A weatherproof control cabinet shall be mounted on
the main tankand provided with means to prevent condensation. (h) A
controlpower isolating switch shallbe supplied. 22.8.2Optional
Accessories Optional accessories may be supplied if specified.(See
Clause 24.9.2.) CAN/CSAC88M90 November1990 Page 78 (Replacesp.78,
August 1990)Licensed for/Autoris Lawrence Duong, Sold by/vendu par
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simple seulement. Le stockage, la distribution ou l'utilisation sur
le rseau est interdit.ii p Notes: (1)Type Ais usedwhere the major
variation of voltage is required atthelow-voltage
terminalandthenormal high-voltage variationisacceptable
onafixedturnwinding. (2)Type Bis used where the major variation of
voltage is required at the high-voltage terminal and the normal
low-voltage variation is acceptable on a fixed turn winding.
(3)Arrangements shown are for singlephase transformers. Figure 5
LTC Transformer Windings CAN/CSAC88M90 November1990 Page 83
(Replaces p.83,August 1990) HVLVHV LV J Type B LTCin HIT Winding
Type A LTCin LV Winding Licensed for/Autoris Lawrence Duong, Sold
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d'utilisateur simple seulement. Le stockage, la distribution ou
l'utilisation sur le rseau est interdit.24.3 Autotransformers Three
basicformsof LTC windings are considered.Type C has the LTC in the
serieswinding.Type D has the LTC in an auto-point winding, and Type
E hasthe LTC in the neutral.(See Figure 6.) Booster transformer
circuits may be used. HV HV LV LV 4C Type CType DType E LTC in
Series LTC at Autopoint LTC in Neutral Notes: (1)Type C is used
where the major variation of voltage is required atthe high-voltage
terminaland the normal low-voltage variation is acceptable on
afixed turnwinding. (2)Type D is used where the major variation of
voltage is required at the low-voltage terminal and the normal
high-voltage variation is acceptable on a fixed turn winding.
(3)Type Fl varies the effective turns of both the high voltage and
the low voltage, but has greater proportional effect on the low
voltage. It is therefore similar to Type D,except that the magnetic
induction willvary with tap-changer position.(A tertiary or other
winding will have avoltage variation as a result of the varying
induction, unless other means are used to prevent such voltage
variation.) (4)Arrangements shown arefor single-phase transformers.
Figure 6 LTC Autotransformer Windings CAN/CSAC88M90 - November1990
Page 84 (Replacesp.84,August 1990) HV 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.General Instruction No.1
CAN/CSA - C88-M90 August 1990 GSA Standard GAN/GSA-G88-M90,Power
Transformersand Reactors, consists of 91 pages,each dated August
1990. This Standard, like all GSA Standards, is subject to periodic
review, and amendments in the form of rep'acement pages may be
issued from time to time; such pages will be mailed automatically
to those purchasers who complete and return the attached card.*
Some Standards require frequent revision between editions, whereas
others require none at all.It is planned to issue new editions of
the Standard, regardless of the amount of revision, at intervals
not greater than 5 years.Except in unusual circumstances,
replacement pages will not be issued during the last year of that
edition. * This card will appear with GeneralInstructionNo. 1 only.
Atthough any reptacement pages that have beenissued will be sold
with the Standard, it is for the purchaser to insert them where
they apply. The responsibility for ensuring that his or her copy is
comptete rests with the holder of the Standard, who should, for the
sake of reference, retain those pages which have been replaced.
Note: A GeneralInstructionsheet will accompanyreplacementpages each
time they are issued and will list the latest date of each page of
the Standard. Cut along dotted line Name Organization Address City
Prov./State CSAStandard Postal/Zip Code_________ CAN/CSAC88M9O
Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le
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on network prohibited./Permis d'utilisateur simple seulement. Le
stockage, la distribution ou l'utilisation sur le rseau est
interdit.Canadian Standards Association Consolidated Mailing List 1
78Rexdale Boulevard Etobicoke, Ontario Canada M9W 1 R3 Place Stamp
Here Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA
on/le 3/25/2010. Single user license only. Storage, distribution or
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Le stockage, la distribution ou l'utilisation sur le rseau est
interdit.National Standard of CanadaCA N/CSA - C88-M90 Power
Transformersand Reactors Preparedby Canadian Standards Association
Approvedby Standards Council of Canada 1SSN 0317-5669 Published/n
August 1990 by Canadian Standards Association 178 Rexdale Boulevard
Rexdale (Toronto), Ontario, Canada M9W 1R3 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.TechnicalEditor:John Davis ManagingEditor:Bernard Kelly
Canadian Standards Association 1990 All rights reserved.No part of
this publication may be reproduced in any form, in an electronic
retrieval system or otherwise, without 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.Contents Technical Committee on Power
Transformers7 Preface9 1. Scope 11 2.Reference Publications11
3.Service Conditions and Loading 13 3.1Intended Use13 3.2Usual
Service Conditions14 3.3Unusual Service Conditions14 3.4 Loading
Beyond Rated MVA15 3.5LowAmbient Temperature Load Capability 16
4.Definitions16 5.Terminal Markings, Polarity, and Angular
Displacement 26 5.1General26 5.2Identification of Windings 27 5.3
Marking of Terminals27 5.4Order of Numbering Terminals28 5.4.1
SinglePhase Transformers28 5.4.2ThreePhase Transformers28
5.5Location of External Terminals and Polarity of SinglePhase
Transformers29 5.5.1Location of External Terminals29 5.5.2 Polarity
29 5.6Location of External Terminals and Angular Displacement of
ThreePhase Transformers29 5.6.1Location of External Terminals29
5.6.2 Angular Displacement 30 5.7Terminal Markings forSeriesVoltage
Regulators 32 6. Types Based on Cooling Methods32 6.1General32 6.2
Cooling Medium32 6.2.1Internal Cooling Medium32 6.2.2External
Cooling Medium32 6.3 Type of Circulation33 6.4 Designations and
Order of Symbols 33 6.5Standard Type Designations 33 6.6 Type
Designation for More than One Method of Cooling 33 7. Ratings 34
7.1Preferred MV'A Ratings 34 7.2Basis of MVA Rating 35 7.3Basis of
Voltage Rating 36 8. voltage Taps for Deenergized Operation 36
CAN/CSAC88-M90 August 1990 - Page 3Licensed for/Autoris Lawrence
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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.9.Temperature Rise37
9.1Conditions Under Which TemperatureRise Limits Apply 37
9.2Limitsof Temperature Rise for Continuous Operation 37 9.3Winding
Conductor Insulation37 10.ShortCircuit Characteristics38
10.1General38 10.2ShortCircuit Current Magnitude 38 10.2.1All
Transformers38 10.2.2TwoWinding Transformers39
10.2.3Autotransformers and Multiwinding Transformers40
10.2.4SeriesVoltage Regulators 40 10.3ShortCircuit Current
Duration41 10.4Limits of Temperature Rise41 10.5Transformer
Terminal and System Conditions41 11.Insulation Levels and
Clearances in Air41 11.1Selection of Insulation Levels for Line
Ends of Windings 41 11.2Selection of Insulation Levels for Neutral
Ends of Windings 41 11.3Selection of Bushings 43 11.4External
Clearances in Air44 12. Stabilizing Windings 45 13.Sound Levels46
14.Tolerances50 15.Mechanical Features and Accessories51
15.1Standard Mechanical Features and Accessories51 15.1.1General51
15.1.2 Liquid Preservation System 51 15.1.3Transformer Tank51
15.1.4 Tap Changer for Deenergized Operation 51 15.1.5Breather52
15.1.6 Moving Facilities52 15.1.7TankAccess52 15.1.8 Emergency
PressureRelief Device52 15.1.9 Marking 52 15.1.10 Liquid Level
Indicator52 15.1.11 Liquid Temperature Indicator52 15.1.12 winding
Temperature Indicator53 15.1.13Automatic Control forFans53
15.1.14Automatic Control for Pumps 53 15.1.15 Liquid Drain Valve53
15.1.16 Liquid Sampling Valve53 15.1.17 Liquid Treatment
Connections53 15.1.18Radiator Valves53 15.1.19water Piping 53
15.1.20 Insulating Liquid Piping 54 15.1.21 Grounding 54
15.1.22Control Cabinets54 15.1.23Instruction Manual54
15.1.24Vacuum/Pressure Gauge 54 15.1.25Sudden Pressure Relay 54
15.1.26Gas Detector Relay 55 CAN/CSAC88M90 August 1990 Page 4
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stockage, la distribution ou l'utilisation sur le rseau est
interdit.15.2 Optional Accessories55 15.3Preferred Voltages for
Auxiliaries and Accessories55 16.Tests56 16.1Method of Making
Tests56 16.2Test Report 56 16.3 Summary of Teststo be Performed56
16.4Dielectric Tests57 16.4.1General57 16.4.2 Applied Potential
Test58 16.4.3Induced Potential Test58 16.4.4 LightningImpulse
Tests60 16.4.5 Switching Impulse Tests63 16.5Lossand Impedance
Tests63 16.6Mechanical Tests64 16.7Core Insulation Tests64
16.8ShortCircuit Test64 16.9SoundLevel Test64 17. Rating Plate65
18.Instruction Manual70 19.Finish71 20.ShuntReactors71 20.1Basis of
Mvar Rating 71 20.2 Operation Above Rated Voltage 71 20.3 Linearity
71 20.4Tests71 20.4.1General71 20.4.2Routine Tests71 20.4.3 Applied
Potential Tests72 20.4.4TurntoTurn Potential Test72 20.4.5 Type
Tests73 20.4.6Other Tests73 21. Grounding Transformers73 21.1Basis
of Rating 73 21.2Limits of Winding Temperature 73 21.3Limits of
Tank Temperature 74 21.4Tolerance for Impedance 74 21.5Mechanical
Strength 74 21.6Accessories74 21.7Tests74 22.
SeriesVoltageRegulators 74 22.1General74 22.2Basis of Rating 74
22.3 Operating Voltage Limits75 22.4Losses and Impedance 75
22.4.1Tolerances for Losses and Impedance 75 22.4.2Excitation
Loss75 22.4.3LoadLoss75 22.4.4 Impedance 76 CAN/CSAC88-M90 August
1990 Page 5 Licensed for/Autoris Lawrence Duong, Sold by/vendu par
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simple seulement. Le stockage, la distribution ou l'utilisation sur
le rseau est interdit.22.4.5Normal Conditions forthe Determination
of Lossesand Exciting Current76 22.5Short Circuits76 22.6Diagram of
Connections76 22.7Rating Plate78 22.8Mechanical Features and
Accessories78 22.8.1Standard Mechanical Features and Accessories78
22.8.2Optional Accessories78 22.9 Accuracy Classes79 22.10Errors
for Accuracy Determination80 22.11Compensator Marking Deviation80
22.12TestTerminals80 22.13Tests81 22.14Sound Levels81
23.Phaseshifting Transformers81 24.Transformers and
Autotransformers with LoadTapchanging (LTC) 81 24.1General81
24.2Multiwinding Transformers82 24.3Autotransformers84
24.4Alternative TapChanger Locations85 24.5 Voltage_Regulating
Range 85 24.6ShortCircuit Characteristics85 24.7Low Ambient
Temperature Capability 85 24.8 Paralleling 85 24.9Controls and
Indicators85 24.10Mechanical Features and Accessories86 24.11
Rating Plate86 Appendices AInformation Required with Enquiry and
Order88 BMechanical Strength ofTransformerstoWithstandExternalShort
CircuitCurrents90 CAN/CSAC88M90 August 1990 Page 6Licensed
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prohibited./Permis d'utilisateur simple seulement. Le stockage, la
distribution ou l'utilisation sur le rseau est interdit.Technical
Committee on Power Transformers G.E. Woolley Ontario Hydro,
Chairman Toronto Representing Canadian Electrical Association J.
AubinHydro-Qubec, Var ennes Representing Canadian Electrical
Association T.A. Bickley Transelectrix Technology Inc., Guelph,
Ontario M.N. Campbell New Brunswick Electric Power Commiss ion,
Fredericton Representing Canadian Electrical Association F.
DavidFederal Pioneer Limited, Winnipeg, Manitoba T. Freyhult ABB
Inc., Varennes, Quebec L.M.Nicholas Moloney Electric Corporation,
Toronto, Ontario D.D. PercoTranselectrix Technology Inc., Guelph,
Ontario Representing Electrical and Electronic Manufacturers
Association of Canada G.PolovickBritish Columbia Hydro, Vancouver
Representing Canadian Electrical Association R.SeoniAcres
International Limited, Niagara Falls, Ontario D.N.SharmaNova Scotia
Power Corporation, Halifax Representing Canadian Electrical
Association R.G.ShurtleffCity of Kingston Public Utilities
Corniniss ion, Kingston, Ontario R.A.VeitchNEI Canada Limited, St.
Catharines, Ontario CAN/CSAC88M90 August 1990 Page 7Licensed
for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le 3/25/2010.
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prohibited./Permis d'utilisateur simple seulement. Le stockage, la
distribution ou l'utilisation sur le rseau est
interdit.G.WeeksAlcan Smelters and Chemicals, Jonquire, Qubec
J.DavisCanadian Standards Association,Standards Rexdale, Ontario
Administrator, Nonvoting CAN/CSAC88M90 August 1990 Page 8Licensed
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prohibited./Permis d'utilisateur simple seulement. Le stockage, la
distribution ou l'utilisation sur le rseau est interdit.Preface
Thisis the fourthedition of CSA Standard C88,Power Transformers and
Reactors.It supersedes the previous editions published in
1947,1968, and 1979. Thisrevision of theStandard includes several
significant changes including general reorganization and
rearrangement.Major changes include the addition of external
airclearances,the elimination of baseMVA limitsfor induced,applied,
and impulse tests, and the elimination of chopped wave tests.A
requirement for measurements of apparent charge in addition to RIV
measurements has been added fortransformers over245 kV.ThisStandard
recognizes atransformerwith forced directed oil flowand permits an
average winding temperature riseof 70C forthesetransformers. A
requirement for thermally upgraded paper has been added.Clauses
referring to prefault operating voltage and external shortcircuit
withstand requirements havebeen clarified. ThisStandard was
prepared by the Technical Committee on Power Transformers underthe
jurisdiction ofthe Standards Steering Committee on Electrical
Engineering, and was formally approved by these Committees.Ithas
been approved as aNational Standard by the Standards Council of
Canada. August 1990 Notes: (1) Use of the masculine gender in
thisStandard is not meant to exclude the feminine gender when
applied to persons.Similarly, use of the singular does not exclude
the plural(and viceversa) whenthe sense allows. (2)Although the
intended primary application of this Standard is stated in its
Scope, it is important to note thatit remains the responsibility of
the user of the Standard to judge its suitability for his
particular purpose. (3) CSA Standards are subject to periodic
review, and suggestions for their improvement willbe referred tothe
appropriate comrnit tee. (4) All enquiries regarding this Standard,
including requests for interpretation, should be addressed to
Canadian Standards Association,Standards Division, 178 Rexdale
Boulevard, Rexdale, Ontario M9W lR3. Requests for interpretation
should (a)definethe problem, making reference tothe specific
clause, and,whereappropriate, include an illustrative sketch;
(b)provide an explanation of circumstances surrounding the actual
field condition; and (c)be phrased where possible to permit a
specific "yes" or "no" answer. Interpretations are published in CSA
Information Update. For subscription details and a free sample
copy, write to CSA Sales Promotions or telephone (416)747-4116.
CAN/CSAC88M90 August 1990 Page 9 Licensed for/Autoris Lawrence
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d'utilisateur simple seulement. Le stockage, la distribution ou
l'utilisation sur le rseau est interdit.CAN/CSAC88M90 August 1990
Page 10Licensed 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.CAN/CSAC8 8M90 Power Transformers and Reactors 1. Scope
1.1 ThisStandard,except asnoted inClause1.2,applies to all
liquidfilled transformers, autotransformers, booster transformers,
loadtapchanging transformers, grounding transformers, phase
shifting transformers,seriesvoltage regulators, and shunt reactors.
Notes: (1) The term"transformer(s)" in this Standard refers tothe
overall unit and not just to the electrical components implied by
the definition. (2) In general this Standard is written in
reference totwo winding transformers,although many requirements
willbe recognized to be common to multiwinding
transformers,autotransformers, load tapchanging transformers, shunt
reactors,and seriesvoltage regulators. Wherethereare special
requirements for these(other) transformers, there are sections
contained herein specifically addressed to them. 1.2 This Standard
doesnot apply to the following: (a) distribution transformers (CSA
Standard C2, Single-Phase and Three-Phase Distribution
Transformers,Types ONAN and LNAN); (b) instrument transformers (CSA
Standard C13,Instrument Transformers); (c)drytype transformers (CSA
Standard C9, Dry-Type Transformers); (d)padmounted transformers
(CSA Standard C227Seriesof Standards); (e) submersible transformers
(CSA Standard C301Seriesof Standards); (f)threephase network
transformers (CSA Standard C199, Three- PhaseNetwork Transformers);
(g) rectifiertransformers, welding transformers, furnace
transformers,starting transformers, testing transformers, or
currentlimiting reactors. Note:In the above list the pertinent CSA
Standard number has been noted wheresuch exists.Where no CSA
Standard exists, this Standard may be used insofar as it applies.
2.Reference Publications 2.1 Where reference ismade to other
publications, such references shallbe considered to referto the
latestedition and any amendments published thereto. CAN/CSAC88-M90
August 1990 Page 11 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 C501976,
Insulating Oil, Electrical for Transformers and Switches;
CAN3C3081985, The Principles and Practice of Insulation
Coordination. ANSI*Standard Si. 41983, Specification for Sound
Level Meters. ANSI/IEEEt Standards 321972,CR1984) Requirements,
Terminology and Test Procedures for Neutral Grounding Devices;
C57.12.OO1987, General Requirements for Liquid-Irrirnersed
Distribution, Power, and Regulating Transformers; C57.12.801978,
CR1986) Terminology for Power and Distribution Transformers;
C57.12.901987, Test Code for Liquid Immersed Distribution, Power,
and Regulating Transformers and Guide for Short-Circuit Testing of
Distribution and Power Transformers; C57.151986, Requirements,
Terminology, and TestCodefor Step-Voltage and Induction-Voltage
Regulators; C57 .211981, Requirements,Terminology, and TestCodefor
Shunt Reactors; C57.921981, Guidefor Loading MineralOil-Immersed
Power Transformersuptoand Including 100MVA with 55Cor 65CWinding
Rise; C57 .981986, Guide for Transformer Impulse Tests; C57
.1131988, Guide for Partial Discharge Measurement in Liquid-Filled
Power Transformers and Shunt Reactors; C57 .1161989 Guide for
Transformers Directly Connected to Generators. CEA# Publications
Guide for Dissolved Gases in Oil Analysis for Transformers and
Reactors During Factory Tests(Revision 11989); Power Transformer
Test Report Format (1989). CAN/CSAC88M90 August 1990 Page
12Licensed 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.EEMACStandards 3611987, Insulating Mineral Oilfor New
Electrical Apparatus; GL131989, PowerTransformer and Reactor
Bushings; L1011969, Load-Tap--Changing Paralleling Schemes;
L1311976, Dielectric Tests and TestProcedures for Power
Transformers; L1411976, Liquid LevelIndicators for Power
Transformers; L1511976, Temperature Indicators for Power
Transformers; Y121979, Performance Specification for Finishing
Systems for Outdoor Electrical Equipment. IEEE** Publication
7561984 (expected tobecome ANSIC57.115), Loading
Mineral-OilImmersed Power Transformers Rated in Excess of 100 MVA.
IECtt Publications 761976, Power Transformers, Part 4,Tappings and
Connections; 2141989, OnLoadTap-Changers; 6161989, Terminaland
Tapping Markings for Power Transformers. *erjcan NationalStandards
Institute tAmerican NationalStandards Institute/Institute of
Electrical and Electronics Engineers +Canadian
ElectricalAssociation Electrical and Electronic Manufacturers
Association of Canada **Institute of Electrical and Electronics
Engineers ttlnternational Electro technical Commission 3.Service
Conditions and Loading 3.1Intended Use All liquidfilled power
transformers and reactors shall be suitable for outdoor service
unless specified for indoor service. CAN/CSAC88--M90 August 1990
Page 13 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.3.2Usual Service Conditions 3.2.1 All transformers and
reactorsshall be suitable for operation under the following
conditions: (a) Altitudea height above sealevel not exceeding
1000m. Note:For higher altitudes, see Clauses 3.3.1and 3.3.3.
(b)Temperature of Cooling Mediumfor watercooled apparatus, cooling
waterat a temperature not exceeding 25Catthe inlet;for aircooled
apparatus, air at a temperature never exceeding 40C, and (i) never
below 50C in the caseof outdoor transformers; or (ii) never below
5C in the caseofindoortransformers. Inaddition,for aircooled
apparatus, an air temperature never exceeding the following values:
(iii) 30C average in any one day; (iv) 20C average in any one year.
Note:For higher temperatures, see Clause 3.32. (c) Wave Shape of
Supply Voltage-a supply voltage of which the wave shape is
approximately sinusoidal. (d)Synimetry of Polyphase Supply
Voltages--for polyphase transformers, supply voltages thatare
approximately symmetrical. 3.2.2 All loadtapchanging (LTC)equipment
must be suitable for operation down to 25C.For lowertemperature
requirements, agreement between the manufacturer and the purchaser
isessential asto the requirement for heating devices or lockout
devices (or both,when required). The lockout device shallbe
actuated by a sensor in the diverter switchoil. 3.3Unusual Service
Conditions The conditions described in Clauses 3.3.1to 3.3.5 may
affect performance and should receive special consideration.
3.3.1Reduced Temperature Rises for Transformers Designed for High
Altitudes Unless otherwise agreed upon between the manufacturer and
the purchaser, for aircooled transformers designed for operation
atan altitude higher than 1000 m,buttested at normal altitudes, the
limits of temperature rise arereduced by the following amounts for
each 500 m by which theintended working altitude exceeds 1000m:
(a)liquidfilled, naturalaircooled transformers, 2.0%;
(b)liquidfilled, forcedair--cooled transformers, 3.0%. 3.3.2Reduced
Temperature Rises for Transformers Designed for HighCooling Medium
Temperatures or Special AirCooling Conditions If the transformer is
designed for service where the temperature of the cooling air
exceeds one of the maximum values shown in Clause 3.2.1(b)by no
more than 10C,the allowable temperature risesfor the windings,
core(s), and liquid shallbereduced. Ifthe base rating is 10 MV'A or
greater, thereduction willbe by the same amount as the cooling air
exceeds the limit.For smaller ratings, the allowable temperature
risesshall bereduced (a)by 5C if theexcess temperature islessthan
or equal to 5C; (b)by 10Cif theexcess temperature is greater than5C
and less CAN/CSAC88M90 August 1990 Page 14Licensed for/Autoris
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prohibited./Permis d'utilisateur simple seulement. Le stockage, la
distribution ou l'utilisation sur le rseau est interdit.thanor
equal to 10C. Where, for aircooled transformers the
excesstemperature of the cooling air exceeds 10Cor, for watercooled
transformers the temperature ofthe cooling water exceeds 25C,the
allowable temperature rises require an agreement between the
manufacturer and the purchaser. Any sitecondition that may
eitherimpose restrictionson the air cooling or produce highambient
air temperatures should be specified by the purchaser.
3.3.3Increased Air Clearance for Transformers Designed for High
Altitudes The puncture strength and the flashover voltage in the
immersion medium are not affected by altitude.In orderto ensure
that the external withstand voltages are notreduced at altitudes
exceeding 1000m,the air clearance normally required must be
increased by a suitable amount.The amount by which theinsulation
level,on whichthe airclearance isbased,should be increased is,for
general guidance, 1.0% for each 100 m in excessof 1000 m above sea
level. Example: Altitude ofinstallation: 2800 m. Increase in
insulation level required(2810) x1.0%18%. Note:The air density at
high altitudes is lower thanat sea level.The dielectric strength of
theair is thus reduced and air clearances that are adequate at
altitudes not exceeding 1000 m may be insufficient at higher
altitudes. (See EEMAC Standard GL1-3, PowerTransformer and Reactor
Bushings.) 3.3.4Other Unusual Service Conditions The following
conditions may affect thetransformer performance and should receive
special consideration: (a)exposure to damaging fumesor vapours,
explosive mixtures of dustsor gases, steam,salt spray, excessive
moisture or dripping water, abnormal vibration, shocksor tilting,
unusual storage or transportation conditions, or unusual space
limitations; (b)frequency of LTC operation, difficulty of
maintenance, harmonic content, unbalanced voltage,special
insulation requirements; (c) excitation exceeding 110%ofratedvolts
per hertz; (d)planned shortcircuits as part of regular operating or
relaying practice; (e)earthquake. 3.3.5Heat Radiation Properties of
Paint Finish Metallic flake paints suchas aluminum,zinc,etc, have
radiation properties thatincrease the temperature riseof
transformers except in direct sunlight. Particular note shouldbe
made of a paint's radiation properties when a transformer is
painted inthe field. 3.4 Loading Beyond Rated MVA The purchaser is
strongly advised to address any needsfor transformer loading
capability beyond nameplate rating atthe time of specification for
purchase, otherwise it can be laterfound that ancillary
equipment,winding leads,internal metallic parts heated
CAN/CSAC88-M90 August 1990 Page 15Licensed 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.by leakage flux,etc,may
restrict loading levelsto below those inherentinthe windings.
Reference should be made tothe ANSI/IEEE guide C57.92 for
transformers with a maximum nameplate rating up to and including
100 MVA, andIEEE 756forthosewith a rating over100 MVA, for afull
description of risksand limitationsof loading beyond nameplate
rating. 3.4.1Generator StepUp Transformer Loading Capability Asthe
requirement for loading capability of a generator stepup
transformerisrelated directly to the output capacity of the
generator to which itis connected, the transformer loading
capability,including low temperaturecapability, shall be specified
by the purchaser. The purchaser is advised toreferto ANSI/IEEE
GuideC57.116 for transformers directly connected to generators.
3.5LowAmbient Temperature Load Capability Transformers,except for
generatorstepup units (see Clause 3.4.1), shall be capable of an
increase in loading for each degree Celsius thatthe daily average
ambient temperature islower than25C, down to a minimum average
ambient temperature of 0C. Selfcooled and watercooled
unitsshallhavean increase of1.0% for each degree Celsius below
25Cand forcedaircooled and forcedair/forcedliquidcooled unitsshall
have an increase of 0.75%for each degree Celsius below 25C.
4.Definitions 4.1 The following definitions apply in thisStandard:
Displacement Angular displacement (of a polyphase transformer)the
time angle,expressed in degrees, between the linetoneutral voltage
of the referenceidentified highvoltage terminal (H1) and the line
toneutral voltage of the corresponding identified lowvoltage
terminal (X1). Note:The preferred connections for pa1 yphase
iransformers are those which result in the smallest possible
phaseangle displacements measured in aclockwise direction from the
line-to neutral voltage of the reference identified high-voltage
terminal (H1).Thus, standard threephase transformers have angular
displacements of either zero or 30. Clock system (of phase
displacement)a method of expressing the phasedisplacement between
two windings by analogy to the hands of a clock. The phasors (taken
torotatein acounter clockwise direction) representing the voltages
between the neutral point (real or imaginary) and the corresponding
terminals of two windings are viewed asthe handsof aclock.The
angular difference between the phasors isexpressed asthe hour
number, with the large (minute) CAN/CSAC88M90 - August 1990 Page
16Licensed for/Autoris Lawrence Duong, Sold by/vendu par CSA on/le
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on network prohibited./Permis d'utilisateur simple seulement. Le
stockage, la distribution ou l'utilisation sur le rseau est
interdit.hand pointing at 12 representing the highvoltage winding,
and the small (hour) hand representing the phasor of the lowor
intermediatevoltage winding. Exciting current (of a transformer)the
current flowing through a lineterminal of a winding when rated
voltage is applied atrated frequency, the other winding(s) being
opencircuited. Grounding Effectively groundedgrounded through a
grounding connection of sufficiently low impedance (inherent or
intentionally added,or both) that ground faultswhich may
occurcannotbuild up voltages in excessoflimitsestablished for
apparatus,circuits,or systems so grounded. Note:An
alternating-current system, or portion thereof,may be said to be
effectively grounded when, for all points on the system, or
specified portion thereof,the ratio of zerosequence reactance to
positivesequence reactance is not greater than3and the ratio of
zerosequence resistance to positivesequence reactance is not
greater than 1, for any condition of operation and for any amount
of connected generator capacity. Groundedthe system,circuit, or
apparatus referred tois connected to ground. Neutral groundedan
intentional ground applied to the neutral conductor orneutral point
of acircuit,transformer, machine, apparatus, or system. Reactance
groundedgrounded through a reactor, a grounding transformer,or
similar reactive device. Resistance groundedgrounded through a
resistor. Solidly grounded (directly grounded)solidly grounded
through a ground connection in which no impedance has been inserted
intentionally. Impedance Impedance (of any tap)the impedance
voltage expressed perunit, or as a percentage ofthe rated voltage
of the tap, when current corresponding to the stated MVA base and
the rated voltage ofthe tap iscirculated through the windings.
Note:The impedance on any tap shallbe given on astated MVA base
(not necessarily rated MVA). Impedance voltage (at rated current
(principaltap)) (a) for two winding transformers, the voltage
required to be applied at rated frequency to the lineterminals of a
winding of a polyphase transformer,ortothe terminals ofa winding of
a singlephase transformer, to cause theratedcurrent to flow through
theseterminalswhen the terminals of the other winding are
shortcircuited; (b) for multiwinding transformers, related to
acertain. CAN/CSAC88M90 August 1990 Page 17 Licensed for/Autoris
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prohibited./Permis d'utilisateur simple seulement. Le stockage, la
distribution ou l'utilisation sur le rseau est interdit.combination
oftwo windings, the voltage required to be applied at rated
frequency to the line terminals for one of the windings of the
combination for a polyphase transformer, orto the terminals of such
a winding for a singlephase transformer,to cause a current to flow
through theseterminals corresponding to the smaller ofthe rated
power valuesof both windings of thatcombination, the terminalsofthe
other windings of the combination being short circuited and the
remaining winding(s)being opencircuited. Notes: (1)(Applicable to
both Items (a) and (b).) The impedance voltage at rated current is
usually expressed as a percentage of the rated voltage of the
winding to which the voltage is applied. (2)(Applicable to Item
(b)only.) In order to simplify certain calculations, it may be
convenient torecalculate the impedance voltages of the various
combinations intermsof the same reference power, whichshould always
beindicated. Reactance voltagethe component of an impedance voltage
in quadrature with the current. Resistance voltagethe component of
an impedance voltage in phase with the current. Zerosequence
impedancethe impedance expressed in ohms per phase atrated
frequency between the terminals of a threephase transformerwhen
allthree phases are excited from a singlephase source. Notes:
(1)The zerosequence impedance is dependent not only on the
connection of the winding to which it is applied, but also onthe
connection of the other winding(s) and of its (their) neutral
point(s). (2) The zerosequence impedance may, in certain
circumstances, be dependent on the value of the current. Transition
impedancea resistor orreactor consisting of one or more units
bridging the tap in use and the tap nextto be used for the purpose
of transferring loadfrom one tap position to theother without
interrupting the current; at the sametimeitlimitsthe circulating
current for the period thatboth tapsare bridged. Impulse Levels
Lightningimpulse levelthe prescribed peak value ofthe
lightningimpulse withstand voltage (full wave). Note:The
lightning-impulse level(LIL) has been corrirnonly referred to
asthe"BIL". Switching impulse levelthe prescribed peak value of the
switching impulse withstand voltage (full wave). Insulation Uniform
insulation (of a transformer winding)the insulation of a
transformer winding when all its endsconnected to terminals have
the same power frequency withstand voltage. CAN/CSAC88M90 August
1990 Page 18Licensed 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.Nonuniform insulation (of a transformer
winding)the insulation of a transformer winding when it has an end
intended for direct or indirectconnection to ground and is designed
with a lower insulation level assigned tothis ground orneutral
winding end. Linedrop compensator (in a voltage regulator)a device
that causesthe voltageregulating relay to increase the
outputvoltage by an amountthat compensates forthe impedance drop in
the circuit between the regulator and a predetermined location
onthe circuit (sometimes referred to asthe"load centre"). Liquid
insulating mediamineral oil orflameretardant insulating liquids.
Liquid Preservation Systems Conservator or expansion tankan
auxiliary liquidtank, to provide for the expansion and contraction
ofthe liquid in the main tankdue to temperature changes.
Conservator or expansion tank systema method ofliquid preservation
in which the main tankremains entirely filled with liquid overthe
temperature rangespecified,by means of a conservatororexpansion
tank. Sealed tank systema method of liquid preservation in which
the interior of the tankis sealed from the atmosphere and in which
the gas plus the liquid volume remains constant overthe temperature
range. Load TapChanger Load tapchanger (LTC)a device for changing
the tap of a winding suitable for operation whilethe transformer
isenergized or onload. Selector switcha switching device capable of
making, carrying, and breaking currents, combining the duties of a
tap selector and a diverter switch. Changeover selectora device
designed to carry current, but not to make or breakcurrent, used in
conjunction with a tap selector or selectorswitchto enableits
contacts and the connected tap to be used more thanonce when moving
from one extreme position to the other. Cycle of operationthe
movement of the tap changer from oneend ofits range tothe otherand
the returnmovement to its original position. Diverter switch-a
switching device used in conjunction with a tap selector to
carry,make,and break current on taps thathave already beenselected
by the tap selector. CAN/CSAC88M90 August 1990 Page 19 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.Driving
mechanismthe means by which the tap changer is actuated. Note:The
mechanism may include independent means of storing energy (eg, a
load spring mechanism) to control the speed and to ensure the
completion of an operation. Tap selectora devicedesigned to carry
current, butnotto make or break current,used in conjunction with a
diverter or arcing switch, to select tap connections. Losses Load
loss (of a transformer)those losses which areincident to the
carrying ofload. Note:Load lossincludes 12R lossin the windings
dueto load current;stray loss due to stray fluxesin the windings,
core clamps,etc; and also the loss due to circulating currents, if
any, in parallel windings or conductors. Excitation loss(of a
transformer)the active power absorbed when rated voltage at rated
frequency is applied to the terminals of one of the windings, the
other winding beingopencircuited. Note:Excitation lossincludes
coreloss, dielectric loss, and 12R lossin the windings due to
exciting current. Total loss(of a transformer)the loss represented
by the sum of the excitation and the load losses; the totallossdoes
notinclude thelosses of auxiliaries such asfan and pump motors.
Phase Connections Delta connectionthe windings so arranged thatthe
phase windings of a threephase transformer, or the windings for the
same rated voltage of singlephase transformers associated in athree
phase bank, are connected inseriesto form a closed circuit.
Starconnectionthe windings so arranged thatone end of eachof the
phasewindings of a polyphase transformer, or ofeachof the windings
forthe same rated voltage of singlephase transformers associated in
a polyphase bank, isconnected to acommon point (the neutral point)
and the otherend to its appropriate line terminal. Zigzag
connectionthe windings so arranged that one end of each phase
winding of a polyphase transformer isconnected to acommon point
(neutral point), and each phase winding consists of two parts in
which phasedisplaced voltages are induced.These two parts normally
have the same number of turns. Polarity Relative lead polarity (of
atransformer)a designation of the relative instantaneous directions
of current inits leads. Notes: (1)Primary and secondary leadsare
said to have the same polarity when, at a given instant during most
of each half-cycle, the current entersan identified, or marked,
primary lead and leaves CAN/CSAC88M90 August 1990 - Page 20
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on network prohibited./Permis d'utilisateur simple seulement. Le
stockage, la distribution ou l'utilisation sur le rseau est
interdit.the similarly identified, or marked,secondary lead inthe
same direction as if the two leadsformedacontinuous circuit. (2)
The relative lead polarity of a singlephase transformer may be
either additiveorsubtractive.If one pair of adjacent leads from the
two winding's isconnectedtogether and voltage applied to one of the
windings, then the relative lead polarity is (a) additive if the
voltage acrossthe other two leads of the windings is greater
thanthat of the higher voltage winding alone; and (b) subtractive
if the voltage acrossthe other two leadsof the windings
islessthanthat of the highervoltagewinding alone. (3) The
relativelead polarity is indicated by identification markson
primary and secondary leadsof like polarity, or by other
appropriate identification. (4) The polarity of a polyphase
transformer is fixed by the internalconnections between phases as
wellas by the relative location of leads; it is usually designated
by means of a phasor diagram showing the angular displacement of
windings and a sketch showing the marking of leads.The phasor lines
of the diagram represent induced voltages and the recognized
counterclockwise direction of rotation is used.The phasor
representing any phase voltage of agiven winding is drawn parallel
to thatrepresenting the corresponding phase voltage of any other
winding under consideration. Ratings Rating (of a power
transformer)--the rated load in MVA together with any other
assigned characteristics, such as voltage, current, and frequency
assigned by the manufacturer.Itshallbe regarded as atest rating
thatdefines an output that can be taken from the apparatus
underprescribed conditions oftest, and within the limitationsof
thisStandard. Continuous ratingthe maximum output in MVA thatcan be
carried continuously without exceeding established temperaturerise
limitations,under prescribed conditions of test, and within the
limitationsof established standards. Shorttime ratingthe maximum
output in MVA thatcan be carried for a specified short time without
exceeding established temperaturerise limitations, underprescribed
conditions of test, and within the limitations of established
standards,and when the transformeris at approximately ambient
temperature at the timethe loadis applied. Base MVA rating (of a
transformer)the sum of the equivalent ONAN ratings of all windings
using the principal tap, divided by two.The base MV'A rating may be
an equivalent rating and is not intended to be athermal rating. For
types of cooling other than ONAN,the equivalent ONAN rating shallbe
obtained by multiplying (a) ONWF rating x0.75; (b) ONAF (ONAN plus
1/3)rating x0.75; (c)ONAF/ONAF CONANrating plus 2/3)rating x0.6;or
(d)OFWF,OFAF,or ODAF rating x0.6. CAN/CSAC88M90 August 1990 Page 21
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on network prohibited./Permis d'utilisateur simple seulement. Le
stockage, la distribution ou l'utilisation sur le rseau est
interdit.Rated MVA (of a transformer)the output thatcan be
delivered continuously, or for thetime specified, at rated
secondary voltage and rated frequency without exceeding the
specified temperature riselimitations under prescribed conditions
of test, and within the limitations of established standards.
Shorttime rating(of a grounding transformer)--the product of the
ratedlineto--neutral voltage at rated frequency and the maximum
constant current thatcan flowin the neutral forthe specified time
without causing specified temperaturerise limitations to be
exceeded, and within the limitations of established standards for
such equipment. Rating of a singlephase seriesvoltage regulator-the
product of the ratedloadin amperes and the rated range of
regulation in volts. Rating of a threephase seriesvoltage
regulatorthe product of the ratedloadin amperes and the rated range
of regulation in volts multiplied by 1.732. Ratio Turns ratio (of a
transforiner)the ratioof the numberofturns in the highvoltage
winding to thatin the lowvoltage winding. Note:Inthe case of a
transformer having taps for changing its voltage ratio,
theturnsratio is basedon the number ofturns corresponding tothe
principal tap of the respective windings to which operating and
performance characteristics are referred. Reactor Reactoradevice
used forintroducingimpedance into an electric circuit,the principal
element of which is inductive reactance. Shuntreactor-areactor
intended forconnection in shuntto an electric system for the
purpose of drawing inductive current. Regulation Voltageregulation
(of a transformer)the change in output (secondary)voltage
thatoccurs when the load is reduced from rated valuetozero, with
the applied (primary)voltage maintained constant. Note:In the case
of multiwinding transformers, the loads on all windings, at
specified power factors, are to be reduced from rated power to zero
simultaneously. The regulation at a given power factor may be
expressed per unitor as a percentage on the base of the rated
secondary voltage. Rated range of regulation (of a seriesvoltage
regulator)the amount thatthe regulator willraise orlowerits rated
voltage with rated voltage applied. Note:The rated range may he
expressed per unit, or as a percentage, of rated voltage; or it may
beexpressed inkilovolts. CAN/CSAC88M90 August 1990 - Page 22
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.Seriesvoltage regulatora transformer having one or more
windings excited from the system circuit or a separate source,and
one or more windings connected in series with the system circuit
for adjusting the voltage in steps, without interrupting the load.
Tap changer for deenergized operationa device for changing the
voltage ratioof the windings; it issuitable for operation only when
the transformer is not energized. Taps Tap (in a transformer)---a
connection brought out of a winding at some point between its
extremities, to permit changing the turns ratio. Full MV'A tap (in
a transformer)a tap through which the transformer can deliver an
output equal to rated MVA without exceeding the specified
temperature rise. Principal tapthe tap corresponding tothe rated
voltage ofthe winding at noload and to which the performance
characteristics are referred. Plus tapatap so located asto
introduce intothe active part of the winding concerned a greater
number of turnsthan those corresponding to the principal tap. Minus
tapatap so located asto introduce into the active part of the
winding concerned fewerturnsthan those corresponding to the
principal tap. Reduced MV'A tap (in a transformer)a tap through
which the transformer can only deliver an output less thanrated MVA
without exceeding the specified temperature rise. Tap rangethe
variation range of the taps expressed as a percentage of the
principal tap, the principal tap being considered as Note:If
thisvariation ranges from 100 -I-ato 100 b,the tap range is said to
be +a per cent, b per cent, ora per cent if ab. Tap stepthe
difference in voltage between two adjacent taps expressed as a
percentage of the principal tap voltage. Temperature Ambient
temperaturethe temperature of the external cooling medium into
which the heatis finally dissipated. In the case of watercooled
transformers, thisisthe temperature ofthe water as it entersthe
waterheat exchanger. Resistance method (of temperature
determination)the determination of the average temperature of a
winding by comparison of the resistance of the winding at the
temperature to be determined with the resistance at a known
temperature. CAN/CSAC88M90 August 1990 Page 23 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.Thermometer
method (of temperature determination)the determination of the
temperature by alcohol thermometers, by resistancethermometers, or
by thermocouples; any of these instruments beingapplied to the
hottest accessible part ofthe apparatus. Temperature risethe
difference between the temperature of the part under consideration
and the temperature of theair, or of the water at the intakeofthe
cooling equipment for aircooled or watercooled transformers,
respectively. Terminals and Neutral Point Terminala conducting
element intended for connecting awinding to external conductors.
Line terminalaterminal for connection to a phase conductor of a
system. Neutral terminal (a) for polyphase transformers and
polyphase banksof singlephase transformers,terminal(s) connected to
the neutral point of astar connected orzigzagconnected winding; and
(b) for singlephase transformers, theterminal intended for
connection to a neutral point of asystem. Neutral pointthe point of
asymmetrical system of voltages that is normally at zero potential.
Note:For astar-connected or zigzagconnected polyphase system, it is
the common point. Tests Acceptance testa testto demonstrate
compliance of a device with the purchaser's requirements.
Dielectric teststests that consist of the application of a voltage
higher thantherated voltage for a specified timefor the purpose of
determining the adequacy against breakdown of insulation materials
and spacing undernormalconditions. Type testa test made on
atransformer thatis representative of othertransformers to
demonstrate thatthesetransformers comply with specified
requirements not covered by routinetests. Note:A transformer is
considered to be representative of others if it is fully identical
in rating and construction, but thetype test may also be considered
valid if it is made on a transformer that has minor deviations of
rating or other characteristics.The acceptability of the type test
in thesecircumstances should be the subject of agreement between
the manufacturer and the purchaser. Routine testatest to which each
individual transformer is subjected. CAN/CSAC88M90 - August 1990
Page 24 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.Thermally upgraded papercellulose paperbased insulation
which has been upgraded from Class 105(Class A) insulation to
inhibit the thermal degradation process. Suchinsulation has alife
characteristic at 120C,marked in terms of tensile strength and
dielectric strength,equal to or better than Class 105cellulose
paper, and should give alifeexpectancy as defined in ANSI/IEEE
Standard C57.92(Figure1) for 65Crisetransformers.(See also
ANSI/IEEE Standard C57.12.80.) Transformers Transformeran electric
device without continuously moving parts that by electromagnetic
induction transfers electric energy from one or more circuits to
one or more othercircuitsatthe same frequency,usually with changed
valuesof voltage and current. Autotransformera transformer in which
part of one winding is commonto both the primary and the secondary
circuits associated withthat winding. Booster transformera
transformerof which one winding is intended to be connected in
series with acircuit in orderto alter its voltage. The other
winding is an energizing winding. Grounding transformera
transformer intended primarily forthe purpose of providing aneutral
point for grounding purposes. Indoortransformer-a transformer
that,because of its construction, must be protected from the
weather. Multiwinding transformera transformer having more than two
windings. Loadtapchanging (LTC) transformera twowinding or
multiwinding transformer having one or more windings provided with
taps and loadtapchanging switchgear for adjusting the voltage in
steps without interrupting the load. Outdoor transformera
transformer of weatherproof construction. Phaseshifting
transformera transformer that advances or retardsthe phaseangle
relationship of one circuit with respect to another. Voltage
Nominal voltage (of a system or circuit)a nominal value assigned to
a system orcircuit of agiven voltage class for the purpose of
convenient designation. Note:The term"nominal voltage" designates
the line-to-line voltage, as distinguished from the line-to-neutral
voltage. It applies to all parts of the system of circuit. Rated
voltage(ofequipment or of a winding)-the voltage to which operating
and performance characteristics are referred. CAN/CSAC88M90 August
1990 Page 25 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.Rated primary voltage (of a
transformer)---the voltage obtained fromthe rated secondary voltage
by applying the turnsratio. Rated secondary voltage (of a
transformer)the voltage at which the transformeris designed to
deliverrated power andto which operating and performance
characteristics are referred. Voltage classificationthe level of
power frequency voltage selected by the purchaser as a basison
which to identify the system of insulation levels and associated
tests applicable to the transformer. Voltageregulating relaya
voltagesensitive device thatis used on an automatically operated
seriesvoltage regulator or LTC transformertocontrol the voltage of
theregulated circuit. Windings Common winding (of an
autotransforiuer)thatpart of the autotransformer winding which is
common to both the primary and the secondary circuits. Series
winding (of an autotransforiuer)thatportion ofthe autotransformer
winding which is not common to both the primary and the secondary
circuits but is connected in seriesbetween the input and output
circuits. Primary windingthe winding on the energy input side.
Secondary windingthe winding on the energy output side. Stabilizing
windinga deltaconnected winding used on star connected transformers
or autotransformers, for any or all ofthe following purposes: (a)
to facilitate the flowof zero phasesequence currents; (b) toreduce
thethirdharmonic voltages inthe transformer windings andin the
system; (c) toreduceinterference with communication circuits due to
thirdharmonic currents in the lines and ground; (d) to stabilize
the neutral point ofthefundamental frequency voltages. Note:The
stabilizing winding may be used to supply a separate load when
adequately rated. 5.Terminal Markings, Polarity, and Angular
Displacement 5.1General Clause 5 specifies the polarity, preferred
methods of connection, and associated angle of phaseshift, and the
method of marking terminals brought out of the transformer tank.The
marking of terminalsinsidethe tankisnot specifically covered,
except that theseterminals shall be marked with numbers or letters
thatwill permit convenient reference and cannotbeconfused with the
marking CAN/CSA-C88M90August 1990 Page 26 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.ofthe
terminals brought out of the tank. Note:It is recognized that from
time to time therewillarise special conditions not covered by
Clause 5and very difficult to cover by any set of general rules.
5.2Identification of Windings 5.2.1 In general, the windings of
atransformer shallbe distinguished from one another as follows:
(a)Twowinding transformers shallhave their windings designated as
High Voltage (HV or H) and Low Voltage (LV or X). (b) Transformers
with more than two windings shallhave their windings designated as
H,X,Y,and Z. (C) Whentransformer windings are physically arranged
with one above the otheronthe core,as, for example, in the caseof
two LV windings designated X and Y,the ratingplate shall indicate
which winding ison top. 5.2.2 The sequence of designations shall be
determined asfollows: (a) The highest voltage winding shallbe
designated as HV or H. (b) The other windings shallbe designated in
order of decreasing voltage as X,Y,and Z. (c) Iftwo(ormore)windings
have thesame voltage and different powerratings, the higher
powerwinding shallreceive the prior letter designation ofthetwo (or
more) letters available, according to the sequence by voltage as
explained above. (d) Iftwo or more windings have the same power and
voltage ratings, the designations of these windings shallbe
arbitrarily assigned. 5.3 Marking of Terminals 5.3.1 In general,
external terminals shallbe distinguished from one another by
marking each terminal with a capital letterfollowed by a subscript
number,eg, for a threephase twowinding transformer the
terminalsofthe H winding would be marked H1, H2, H3; the
terminalsofthe X winding would be marked X1,X2, X3, etc. 5.3.2 The
markings shallbe so applied thatif,for example, the phase sequence
of voltage on the highest voltage winding isinthe time order H1,
H2, H3, itwill be in thetimeorder of X1, X2,X3 and Y2, Y3, etc,on
the otherwindings. 5.3.3 A neutral terminalof athreephase
transformer shall be marked with the proper letter followed by a
subscript 0;eg, H0,X0, etc. A neutral terminalcommon to two or more
windings of a single or threephase transformer shallbe marked with
thecombination ofthe proper winding letters,each followed by the
subscript 0;eg, H0X0, asin the caseof autotransformers. Note:A
terminalbrought out from the winding for some other use thanthatof
a neutral terminal (eg, a 50% starting tap) shall be CAN/CSAC88M90
August 1990 Page 27Licensed 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.marked as a tap terminal.
5.3.4 If a transformer has a twoterminal winding with oneterminal
grounded and the other ungrounded, the subscript 2terminal shall be
the grounded terminal. 5.4Orderof Numbering Terminals 5.4.1
SinglePhase Transformers 5.4.1.1 Except as specified in Clause
5.4.1.2,theterminals of any winding brought out of thetankshall be
numbered 1,2,3,4,5,etc,the lowest and highest numbers marking
thefull winding and the intermediatenumbers marking fractions of
windings or taps. All numbers shallbe so applied thatthe potential
difference from any terminal having a lower number toward any
terminal having a higher numbershallhavethe same sign at any
instant. 5.4.1.2 Inthe case of singlephase autotransformers, the
highvoltage and lowvoltage terminals shall be considered as
belonging to two entirely separate windings and numbered
accordingly. The common neutral terminal shall,however, be marked
with the combination of the appropriate winding letters and
numbers, eg, H2X2. 5.4.1.3 Ifa winding isdivided intotwo or more
parts for seriesmultiple connections and theterminals of these
parts are brought out ofthe tank, Clause 5.4.1.1 shall apply for
the seriesconnection, with the addition thattheterminals of each
portion of the winding shall be given consecutive numbers.
5.4.2ThreePhaseTransformers 5.4.2.1 Marking of Full Winding
Terminals The threeterminals for each winding that connect to
thefull phase windings shall be marked H1, H2,H3, X1,X2, X3,Y3,
etc, respectively. 5.4.2.2 Tap Terminals Where tap terminals are
brought out ofthetank (neutral terminal excepted)they shallbe
marked withthe proper letterfollowed by the numbers 4,7,etc,for one
phase,5,8,etc, for another phase, and 6,9,etc,forthe third phase.
For delta connection, the order of numbering tap terminals shall be
as follows:4,7,etc, from terminal 1toward terminal 2;5,8, etc,from
terminal 2toward terminal 3;.and 6,9,etc, from terminal 3toward
terminal 1. For starconnection, the orderof numbering tap terminals
shall be as follows:4,7,etc, from terminal 1toward neutral;5,8,
etc,from terminal 2toward neutral; and 6,9,etc,from terminal 3
towardneutral. CAN/CSAC88M90 August 1990 - Page 28Licensed
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.5.4.2.3
Interphase Connections Made Outside the Transformer Tank Where the
interphase connections are made outside the tank,the terminals
shallbe marked with the proper letterfollowed by the numbers
1,4,7,10,etc,for one phase;2,5,8,11,etc,for the second phase; and
3,6,9,12, etc,for the third phase. The markings shallbe so applied
that,when a starconnection is made by joiningtogether the highest
numbered terminals of each phase, all rules here given apply,except
those outlined in Clause 5.3.3 5.5Location of External Terminals
and Polarity of SinglePhase Transformers 5.5.1Location of External
Terminals 5.5.1.1 The H1 terminalshall be brought out as the
righthand terminal of the highvoltage group asseen when facing the
highest voltage side of the tank, and other H terminals shall be
brought out in numerical orderfrom right to left. 5.5.1.2 When the
highvoltage winding has only one terminal brought out through a
ratedvoltage bushing (the other terminal to be grounded), the
grounded terminal shallbe designated as H2. For polarity marking
and testing, the H1 terminal shallbe considered as located on the
right,regardless of its actual location. 5.5.1.3 When the
highvoltage terminals are brought out through two bushings of
different insulation levels, the bushing having the higher voltage
level shallbe designated as H1 and shall be located on the
righthand side facing the highvoltage side ofthetank. 5.5.1.4
Singlephase autotransformer terminals shall,asfar as practicable,
be marked in accordance with the requirements for subtractive
polarity specified in Clause 5.5.2.1. 5.5.2 Polarity 5.5.2.1
Subtractive polarity shallbe standard for all singlephase power
transformers.Forsubtractive polarity the lowvoltage terminal
adjacent to H1 shall be marked X1. 5.5.2.2 The same will apply
between the H and Y winding, and between the H and Z winding, where
such windings exist. 5.6Location of External Terminals and Angular
Displacement of ThreePhase Transformers 5.6.1Location of External
Terminals CAN/CSAC88M90 August 1990 Page 29 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.5.6.1.1 The
H1 terminal shall be brought out as the righthand terminal of the
highvoltage group as seen when facing the highest voltage side of
the tank.The H2 and H3 terminals shall be brought outso that the
threeterminalsare arranged innumerical order reading from right to
left when facing the highest voltage side of the tank. The
preferred location ofthe H0 terminal,if present, shallbe to the
right of the H1 terminal as seenwhen facing the highest voltage
sideof the tank. 5.6.1.2 The X1 terminal shallbe brought out as the
lefthand terminal of the X group as seen when facing the X winding
sideof thetank. The X2 and X3 terminalsshallbe brought out
sothatthe three terminals are arranged in numerical order reading
from leftto right when facing the X winding side of the tank. The
preferred location ofthe X0 terminal, if present, shall be to the
leftofthe Xj terminal as seenwhen facing the X winding sideofthe
tank. 5.6.1.3 The Y winding and Z winding terminals, if present,
shall be brought out and numbered in the samemanner asthe X winding
terminals. 5.6.1.4 Autotransformer terminals shall, as faras
practicable, be marked in accordance withthe requirements for
corresponding multiwinding transformers. 5.6.2Angular Displacement
5.6.2.1 The convention for the direction of rotation ofthe voltage
phasors shall be taken as counterclockwise. 5.6.2.2 In orderthatthe
markings of terminal connections between phases of a threephase
transformer indicate definite phase relations, they shallbe madein
accordance withone ofthe threephase groups shownin Figure 1.
5.6.2.3 The preferred angular displacement between windings of
threephase power transformers with deltadelta, starstar,
deltazigzag, or zigzagdelta connections shall be00(see Figure 1).
5.6.2.4 The preferred angular displacement between windings of
threephase power transformers with stardelta, deltastar,
starzigzag, or zigzagstar connections shall be 300 with thelow
voltage neutral phasorlagging (see Figure 1). 5.6.2.5 For
multiwinding transformers, the phasor forthe highest voltage
winding shallremain thereference phasor, and the symbol for this
winding shallbe given first.Other symbols shallfollow in the
CAN/CSAC88M90 August 1990 Page 30Licensed 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.orderof the rated voltages
of the windings. P GROUP 2 ANGULAR DISPLACEMENT GROUP1 T__ANGULAR
DISPLACEMENT 300 00 X2 H2X2 H1A DELTA-STAR (Dd 0)(Dy 1) Xl H3Xi la
X3 Hi lb H3 2b X2 H2X2 STAR-STAR (YyO) HiH3X3 lc H2 STAR-DELTA
(Ydl) xi Hi H3 2c X3 2dld xl X3 Note:Letters in brackets are IEC
designations for winding connections.Figures in brackets are IEC
designations for angular displacement basedon the clock-hour
system. See definition for clock system (of phase displacement) in
Clause 4of this Standard and IEC Publication No. 76, Part 4. Figure
1 Angular Displacement of ThreePhase Transformer 5.7Terniinal
Markings for SeriesVoltage Regulators 5.7.1 Terminals that are
connected to the load shall be designated by an L,and those
connected tothesourceshallbe designated by an S. Example:
Inthecaseof asingle-phaseregulator, theterminalswouldbe marked5,L,
andSL. Inthecaseof athree-phaseregulator, theterminalswouldbe
marked Si,S3,L1,L2,L3,and, if a neutralterminalis provided,50L0.
5.7.2 For threephase regulators, when facing the sourceside of the
regulator, the S terminal shall be brought out on the right, and
CAN/CSAC88M90 August 1990 Page 31 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.the S2 and S3 terminals
shallbelocated in numerical order, reading from right to left.The
L1 terminal shall be brought out as the lefthand terminal of the L
group as seen when facing the load sideof the tank,andthe L2 and L3
terminals shall belocated in numerical order,reading from leftto
right. 5.7.3 The 50L0 terminal, if present, shall be located to the
leftof the S3 terminal as seenwhen facing the sourceside ofthe
tank. 6. Types Based on Cooling Methods 6.1General Liquidfilled
transformers shallbe classified as outlined in Clauses 6.2 to
6.6,based on the cooling methods used. Note: Energy losswithin the
windings,core, and other parts of the apparatus is released as heat
to the cooling medium within the tank.Circulation of the cooling
medium allows thisheat to be dissipated by means of radiators or
heat exchangers. 6.2 Cooling Medium 6.2.1Internal Cooling Medium
The internal cooling medium shall be designated as follows:
SymbolCooling medium 0A mineral insulating oil conforming to CSA
Standard C50 and EEMACStandard B6l LA flameretardant insulating
liquid 6.2.2External Cooling Medium The external cooling medium
shall be designated as follows: SymbolCooling medium AAir WWater
6.3 Type of Circulation The type of circulation for both
internaland external cooling mediums shallbe designated as follows:
SymbolType of circulation NNatural FForced DForceddirected
(internalcooling medium only) CAN/CSAC88M90 August 1990 Page
32Licensed 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.Note:In forced-directed flow, the oilis directed from the
coolers intothe inletductsof all or some windings of the
transformer, so as to pump the oil through the windings. 6.4
Designations and Orderof Symbols The designations and orderof
symbols shallbe as shownin Table 1. Table 1 Designations and Order
of Symbols 1st Letter2nd Letter3rd Letter4th Letter Internal
coolingType ofinternalExternal coolingType ofexternal
mediumcirculationmediumcirc ulation 6.5Standard Type Designations
The standard types of transformers with their designations shall be
as follows: Standard Type Designation (a) Oilfilled natural cooling
ONAN; (b) Oilfilled water cooling ONWF; (c) Oilfilled forcedair
cooling ONAF; (d) Oilfilled forcedoil water cooling OFWF; (e)
Oilfilled forcedoil forcedair cooling OFAF; (f) Oilfilled
forceddirected oil forcedair coolingODAF; (g) Oilfilled forcedoil
natural coolingOFAN; (h) Flameretardant liquidfilled natural
coolingLNAN; (i) Flameretardant liquidfilled water cooling LNWF;
(j) Flameretardant liquidfilled forcedair cooling LNAF; (k)
Flameretardant liquidfilled forcedliquid water cooling LFcF; (1)
Flameretardant liquidfilled forcedliquid forcedair cooling LFAF;
(m) Flameretardant liquidfilled forcedliquid natural cooling LFAN.
6.6 Type Designation for More Than One Method of Cooling Where the
apparatus has more thanone method of cooling, the type designations
for all methods shall be stated, separated from each other by an
oblique (/). In all casesof multiple cooling, the power for each
stage of cooling shallbe designated. Note: Typical exa.inples are
(a)ONAN/ONAF 30/40 MVA--an oil-filled transformer having a
naturally cooled (ONAN) rating of 30 MVA and aforced-air-cooled
(ONAF)rating of 40MVA; (b)ONAN/ONAF/ONAF 30/40/50 MVA--a
transformer having a naturally cooled CONAN) rating of 30 MVA, a
forced-air-cooled (ONAF) rating of 40MVA achieved by operating only
part of the fans, and an increased forced-air-cooled (ONAF) rating
of 50MVA when allthe fansare operating; (c)ONAN/ONAF/OFAF 30/40/50
MV'A--a transformer having a naturally cooled (ONAN) rating of 30
MVA, aforced-air-cooled (ONAF) rating CAN/CSAC88M90 August 1990
Page 33Licensed 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.ot 40 MVA with only the tans operating, and a torced-oil
torced- air-cooled (OFAF) rating ot 50MV'A with both tansand oil
pumps operating; and (ci)ONAN/ONAF/ODAF 30/40/50 MV'A--a
transtormer having a naturally cooled (ONAN) rating ot 30 MVA, a
torced-air-cooled (ONAF) rating of 40 MVA with only the fans
operating, and a forced-directed oil- torced-air-cooled (ODAF)
rating ot 50 MVA with both tans and pumps operating. For ODAF
theinstruction bookfor the transformer shall identify windings with
and without forceddirected flow cooling. 7. Ratings 7.1Preferred
MVA Ratings The preferred MVA ratings are statedin Table 2for
singlephase and threephase twowinding transformers, multiwinding
and auto transformers when only two sets of terminals are brought
out of the tank, and shuntreactors (for basis of Mvar rating see
Clause 20.1). Table 2 Preferred MVA Ratings for Transformers
Preferred ratings in MVA 0.5550500 0.676.6766.7667 0.838.3383.3833
110100 1.2512.5125 Singlephase 1.6716.7167 220200 2.525250
3.3333.3333 440400 1.5151501500 2202002000 2.525250 330300
3.7537.5375 Threephase 550500 660600 7.575750 101001000 121201200
Note:For multiple-rated transformers, the preferred MVA rating tor
theONAN rating is according toTable 2; tor the tirst stage ot
torced cooling(ONAF)thepreterredincrease is 33%, and torthe second
stage ottorced cooling (ONAF/ONAFor OFAF)the preterred
CAN/CSAC88M90 August 1990 Page 34 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.increase is 66? of the ONAN
rating. 7.2Basis of MVA Rating 7.2.1 The rating ascribed shallbe
that output the transformer can deliver atits ratedsecondary
voltage underservice conditions outlined in Clause 3, without
exceeding the temperaturerise limitations specified in Clause 9.
Notes: (1) The rated MV'A isthe product of the secondary kA, the
secondary kV, and the appropriate phase factor (/3 for three-
phase). (2) Unlessotherwise specified, it is assumed thatthe energy
flowsfrom the high-voltage tothe lowvoltage winding. 7.2.2 The MV'A
rating shall be based on ratedsecondary voltage maintained by
impressing on the primary winding the voltage necessary to
compensate forthe effectof regulation of the transformerat
ratedsecondary current and at a power factor of90% lagging. 7.2.3
An autotransformer with a stabilizing winding for connection to an
external load,or amultiwinding transformer with more than two
setsof leads brought out ofthe tank, has no standard basis of power
rating. All simultaneous loading conditions shall be clearly
specified by the purchaser. Foreach loading condition, the MV'A
rating and power factor shall be specified for all windings. 7.2.4
Transformers or autotransformers withan LTC in the secondary
winding shall have reduced MV'A capacity on all tapchanger
positions that givevoltages below the principal rated tap voltage.
The current rating forsuch lowervoltage positions shall be that of
the principal rated tap voltage position. 7.3Basis of Voltage
Rating 7.3.1 The voltage ratings shallbe based on theturnsratio,ie,
noload values. Note:The ratioof voltages willbe subject to the
effect of regulation atthe various loadsand power factors. 7.3.2
Transformers shallbe capable of delivering rated output MV'A, at a
power factorof 90%lagging with 5%above ratedsecondary voltage,
without exceeding thetemperature ises as defined in Clause 9. 7.3.3
Transformers shallbe capable of operating at noload with the
primary voltage required forthe conditions of Clause 7.3.2, or10%
above ratedvoltage, whichever is the higher, without exceeding the
temperature rises as defined in Clause9. CAN/CSAC88M90 - August
1990