1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA ST 20-2014Dry Type Transformers for General ApplicationsNEMA ST 20-2014 Dry Type Transformers for General Applications Published by: National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Vi
2、rginia 22209 www.nema.org Copyright 2014 by the National Electrical Manufacturers Association. All rights including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and P
3、an American Copyright Conventions. 2014 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons engaged in the development and approval of the document at the time it was developed. Consensus
4、 does not necessarily mean that there is unanimous agreement among every person participating in the development of this document. The National Electrical Manufacturers Association (NEMA) standards and guideline publications, of which the document contained herein is one, are developed through a vol
5、untary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA administers the process and establishes rules to promote fairness in the development of consensus, i
6、t does not write the document and it does not independently test, evaluate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any personal injury, property, or other damages
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8、ny information published herein, and disclaims and makes no warranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the performance of any individual manufacturer or sellers products or services by virtue of this stan
9、dard or guide. In publishing and making this document available, NEMA is not undertaking to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely
10、 on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standards on the topic covered by this publication may be available from other sources, which the u
11、ser may wish to consult for additional views or information not covered by this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, designs, or installations for safety or health p
12、urposes. Any certification or other statement of compliance with any health or safetyrelated information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. ST 20-2014 Page i 2014 National Electrical Manufacturers Associatio
13、n CONTENTS Page Foreword vii Scope . viii Section 1 REFERENCED STANDARDS AND DEFINITIONS 1 1.1 REFERENCED STANDARDS. 1 1.2 DEFINITIONS 2 1.2.1 Accessible 2 1.2.2 Accessible, Readily . 2 1.2.3 Accessories . 2 1.2.4 Alternating Current 2 1.2.5 Ampacity 2 1.2.6 Circuit . 2 1.2.7 Combustible Materials .
14、 3 1.2.8 Contactor . 3 1.2.9 Cooling Systems 3 1.2.10 Crest 3 1.2.11 Current . 3 1.2.12 Cycle 4 1.2.13 Diagrams . 4 1.2.14 Dielectric Testing . 4 1.2.15 Distance . 5 1.2.16 Distribution Center (Secondary Distribution) . 5 1.2.17 Duty . 5 1.2.18 Enclosures . 5 1.2.19 Equipment 5 1.2.20 FCAN . 6 1.2.2
15、1 FCBN . 6 1.2.22 Frequency 6 1.2.23 Grounded . 6 1.2.24 Hertz 6 1.2.25 Impedance . 6 1.2.26 Insulation . 6 1.2.27 Interlock . 6 1.2.28 IR-drop Compensation 6 1.2.29 K Factor . 6 1.2.30 Load (output) . 7 1.2.31 Losses . 7 1.2.32 Nonenclosed 7 1.2.33 Overcurrent Protection 7 1.2.34 Part 7 1.2.35 Rati
16、ng 7 1.2.36 Ratio 8 1.2.37 Reactor 8 1.2.38 Regulation of a Transformer 8 1.2.39 Resistant (used as a suffix) . 8 1.2.40 Taps . 9 1.2.41 Temperatures 9 1.2.42 Transformer . 9 1.2.43 Knockout 11 1.2.44 Twistout . 11 1.2.45 Multiple Knockout 11 1.2.46 Windings 11 ST 20-2014 Page ii 2014 National Elect
17、rical Manufacturers Association 1.2.47 Wiring or Busing Terminal, Screw, and/or Lead 12 Section 2 RATING STANDARDS 13 2.1 RATINGS AND PRIMARY TAPS 13 2.2 VOLTAGE RANGES . 13 Section 3 DESIGN AND MARKING 17 3.1 DESIGN AND CONSTRUCTION 17 3.2 MEANS OF HANDLING 17 3.3 TRANSFORMER ENCLOSURE . 17 3.3.1 G
18、eneral 17 3.3.2 Corrosion Resistance 17 3.3.3 Outdoor 18 3.4 OPENINGS 20 3.4.1 Enclosure . 20 3.4.2 Wiring and/or Terminal Compartment . 20 3.4.3 Conduit Entrance Threaded 22 3.4.4 Conduit Entrance Knockouts . 22 3.4.5 Cord and Wire Entry Holes 22 3.4.6 Covers, Bottoms, or Panels . 22 3.5 WALL-MOUNT
19、ED ENCLOSURES 22 3.6 TESTING A KNOCKOUT SURROUNDED BY MULTIPLE TWISTOUTS 22 3.7 THERMAL RATING . 23 3.8 CLASSIFICATION OF INSULATING MATERIALS . 23 3.9 CLASSIFICATION OF INSULATION SYSTEMS 24 3.9.1 Systems Testing 24 3.9.2 System Limiting Temperature 24 3.9.3 Typical Materials Used in 105C Insulatio
20、n Systems 24 3.9.4 Typical Materials Used in 130C Insulation Systems 24 3.9.5 Typical Materials Used in 150C Insulation Systems 25 3.9.6 Typical Materials Used in 180C Insulation Systems 25 3.9.7 Typical Materials Used in 200C Insulation Systems 25 3.9.8 Typical Materials Used in 220C Insulation Sys
21、tems 25 3.9.9 Typical Materials Used in Insulation Systems rated above 220C 25 3.10 COIL INSULATION 25 3.11 INTERNAL WIRE, CABLE, AND BUS 26 3.12 CORROSIVE MATERIALS 26 3.13 FLEXIBLE CORDS 26 3.14 SWITCHES, CIRCUIT BREAKERS, CONTROL DEVICES, ETC. . 26 3.15 CAPACITORS . 26 3.16 LIMITS OF WINDING TEMP
22、ERATURE RISE FOR CONTINUOUSLY RATED TRANSFORMER . 27 3.17 MAXIMUM ALLOWABLE TEMPERATURE RISE FOR MATERIALS AND COMPONENT PARTS 28 3.18 REFERENCE TEMPERATURE FOR EFFICIENCY, LOSSES, IMPEDANCE, AND REGULATION . 29 3.19 TRANSFORMER SURFACE TEMPERATURES 29 3.19.1 Transformer Surface Temperature of 90C (
23、194F) or Less . 29 3.19.2 Transformer Surface Temperature Rise When Tested While Mounted In An Alcove29 3.19.3 Marking 30 3.20 TEMPERATURE RISE OF TRANSFORMER TERMINATIONS FOR FIELD CONNECTIONS 31 3.21 CLEARANCE BETWEEN TERMINALS FOR FIELD CONNECTIONS 31 3.22 BONDING OF CORE 32 3.23 CONTACT SURFACES
24、 OF GROUNDING TERMINALS . 32 3.24 MARKING 32 3.25 NAMEPLATES. 32 ST 20-2014 Page iii 2014 National Electrical Manufacturers Association 3.26 DESIGNATION OF VOLTAGE RATINGS OF WINDINGS . 32 3.26.1 General 32 3.26.2 Single-Phase . 33 3.26.3 Three-Phase 33 3.27 AUTOTRANSFORMERS 33 3.28 TAP 34 3.29 TERM
25、INAL MARKINGS 34 3.29.1 Scope and Purpose . 34 3.29.2 Precautions 34 3.29.3 Location of Markings . 34 3.29.4 Markings 34 3.29.5 Significance of the Terminal Letter 34 3.29.6 Significance of the Numeral 0 (Zero) . 35 3.29.7 Significance of Numerals on Terminals . 35 3.29.8 Definition of Phase Sequenc
26、e . 35 3.29.9 Direction of Rotation of Vectors . 35 3.29.10 Markings of Terminals and Identification of Windings . 35 3.29.11 Single-Phase Transformers . 36 3.29.12 Three-phase Transformers 37 3.29.13 Three-Phase to Six-Phase Transformers 40 3.30 FIELD CONNECTIONS . 41 3.31 CONNECTION OF TRANSFORMER
27、S FOR SHIPMENT . 41 3.32 AUDIBLE SOUND LEVELS . 42 Section 4 TESTING 43 4.1 CLASSIFICATION OF TESTS 43 4.1.1 Routine Tests 43 4.1.2 Design Tests 43 4.1.3 Prototype Tests . 43 4.1.4 Tests for Dry-Type Transformers 43 4.2 ROUTINE, DESIGN, AND PROTOTYPE TESTS . 45 4.2.1 Ratio Tests. 45 4.2.2 Polarity a
28、nd Phase-Relation Tests 47 4.2.3 Method of Polarity Test 48 4.2.4 Phase-Relation Tests 50 4.2.5 Total Losses 53 4.2.6 No-Load Losses (Excitation Losses) . 53 4.2.7 Excitation Current (No-Load Current) 58 4.2.8 Impedance and Load Loss 60 4.2.9 Dielectric Tests 67 4.2.10 Audible Sound Level Tests 69 4
29、.2.11 Resistance Measurements 70 4.2.12 Temperature Tests 73 4.2.13 Short-Circuit Capability 80 4.3 REGULATION AND EFFICIENCY 82 4.3.1 Regulation of a Transformer 82 4.3.2 Efficiency . 83 4.4 ENCLOSURE COMPRESSION TEST 83 Section 5 APPLICATION . 85 5.1 SELECTION OF RATED TRANSFORMER kVA 85 5.2 USUAL
30、 TEMPERATURE AND ALTITUDE SERVICE CONDITIONS. 85 5.3 UNUSUAL TEMPERATURE, ALTITUDE, AND ENVIRONMENTAL SERVICE CONDITIONS 85 5.3.1 Higher or Lower Ambient Temperatures . 85 5.3.2 Application at Altitudes Greater than 3300 Feet 85 5.3.3 Environmental Conditions 85 ST 20-2014 Page iv 2014 National Elec
31、trical Manufacturers Association 5.3.4 Impact Loading 86 5.3.5 Overexcitation 86 5.4 LOADING . 86 5.5 PARALLEL OPERATION 86 5.6 AUTOTRANSFORMERS 86 5.6.1 Advantages and Disadvantages 86 5.6.2 Autotransformer Delta Systems Grounding . 87 5.6.3 Autotransformers in Wye Systems 87 5.6.4 Precautions in C
32、onnecting Autotransformers 87 5.7 SINGLE-PHASE TRANSFORMER CONNECTIONS FOR THREE-PHASE BANKS . 88 5.8 USE OF TRANSFORMERS IN CONNECTING SYSTEMS OF VARIOUS PHASE DISPLACEMENTS 88 5.8.1 0-Degree Phase Displacement Delta-Delta or Y-Y 89 5.8.2 30-Degreee Phase Displacement Delta-Y or Y-Delta 89 5.8.3 60
33、-Degree Phase Displacement Delta-Y or Y-Delta 89 5.8.4 90-Degree Phase Displacement . 89 Section 6 INSTALLATION . 91 6.1 INSPECTION PRIOR TO ENERGIZATION 91 6.2 HANDLING 91 6.2.1 Handling in Inclement Weather . 91 6.2.2 Precautions in Lifting . 91 6.2.3 Skidding or Rolling . 91 6.2.4 Protection of A
34、ccessories 91 6.3 GROUNDING 91 6.4 ROOM REQUIREMENTS . 92 6.5 OUTDOOR APPLICATIONS . 92 6.6 MAINTENANCE ACCESSIBILITY 93 6.7 PERSONNEL AND PUBLIC SAFETY . 93 Section 7 MAINTENANCE . 94 7.1 MAINTENANCE 94 Appendix A LOADING . 95 Appendix B UNITED STATES EFFICIENCY REGULATIONS . 96 TABLES 2-1 KILOVOLT
35、AMPERE AND VOLTAGE RATINGS AND PRIMARY TAPS FOR SINGLE PHASE TRANSFORMERS HAVING PRIMARY VOLTAGES UP THROUGH 600 VOLTS . 14 2-2 KILOVOLTAMPERE AND VOLTAGE RATINGS AND PRIMARY TAPS FOR THREE PHASE TRANSFORMERS HAVING PRIMARY VOLTAGES UP THROUGH 600 VOLTS . 15 2-3 OTHER DESIGNATIONS FOR SYSTEMS IDENTI
36、CAL TO THE NOMINAL VOLTAGE 16 3-1 THICKNESS OF SHEET METAL . 19 3-2 KNOCKOUTS 21 3-3A AVERAGE WINDING TEMPERATURE RISE FOR TRANSFORMERS 10 kVA AND BELOW . 27 3-3B AVERAGE WINDING TEMPERATURE RISE FOR TRANSFORMERS ABOVE 10 kVA . 28 3-4 MAXIMUM ALLOWABLE TEMPERATURE RISES FOR MATERIALS AND COMPONENT P
37、ARTS 28 3-5 REFERENCE TEMPERATURE 29 3-5A MAXIMUM TRANSFORMER ENCLOSURE TEMPERATURE RISE WHEN MOUNTED IN ST 20-2014 Page v 2014 National Electrical Manufacturers Association ALCOVE . 30 3-6 WIRING COMPARTMENT MARKING . 31 3-7 MINIMUM SPACINGS AT FIELD WIRING TERMINALS . 31 3-8 TERMINAL LETTER . 34 3
38、-9 AVERAGE SOUND LEVEL 42 4-1 TESTS FOR DRY TYPE TRANSFORMER 44 4-2 TOLERANCES FOR SINGLE-PHASE AND THREE-PHASE TRANSFORMERS LOSSES 53 4-3 HYSTERESIS AND EDDY-CURRENT VALUES . 56 4-4 APPLIED POTENTIAL TEST VOLTAGES 68 4-5 INDUCED-POTENTIAL TEST DURATION 69 4-6 SOUND LEVEL CORRECTIONS . 70 4-7 EMPIRI
39、CAL FACTOR F 79 4-8 SHORT-CIRCUIT CURRENT MAGNITUDE AND DURATION 81 4-9 TEMPERATURES RESULTING FROM SHORT-CIRCUIT CURRENTS. 81 4-10 POWER FACTOR AND REACTIVE FACTOR . 83 5-1 SUMMARY OF PRECEDING EXAMPLES . 90 FIGURES 3-1 DIAGRAM OF TEST PLATE SHOWING AREA OF SUPPORT WITH RESPECT OF AREA TO TWISTOUTS
40、 . 23 3-2 TRANSFORMER MOUNTED IN AN ALCOVE 30 3-3 VECTOR ROTATION 35 3-4 SIMPLE H AND X WINDINGS WITHOUT TAPS . 36 3-5 SIMPLE H WINDING WITH TAPS SERIES-PARALLEL X WINDING 37 3-6 SERIES-PARALLEL H WINDING WITH TAPS SERIES-PARALLEL X WINDING 37 3-7 AUTOTRANSFORMER 37 3-8 TERMINAL MARKINGS AND VOLTAGE
41、 DIAGRAMS FOR THREE-PHASE TRANSFORMER CONNECTIONS . 39 3-9 ANGULAR DISPLACEMENT AND TERMINAL MARKINGS FOR SIX PHASE TRANSFORMERS 41 4-1 RATIO BY COMPARISON 46 4-2 ALTERNATE COMPARISON METHOD 47 4-3 RATIO BY RATIO BRIDGE 47 4-4 POLARITY OF TRANSFORMERS, EXAMPLE A 49 4-5 POLARITY OF TRANSFORMERS, EXAM
42、PLE B 49 4-6 POLARITY BY ALTERNATING VOLTAGE TEST . 49 4-7 POLARITY BY RATIO BRIDGE . 50 4-8 DETAILS OF PHASE RELATION TESTS FOR THREE-PHASE TRANSFORMERS 51 4-9 DETAILS OF TEST FOR PHASE RELATIONSHIPS FOR SIX-PHASE TRANSFORMERS 52 4-10 CONNECTIONS FOR THE EXCITATION TEST OF A SINGLE-PHASE TRANSFORME
43、R WITHOUT INSTRUMENT TRANSFORMERS 54 ST 20-2014 Page vi 2014 National Electrical Manufacturers Association 4-11 CONNECTIONS FOR THE EXCITATION TEST OF A SINGLE-PHASE TRANSFORMER WITH INSTRUMENT TRANSFORMERS . 55 4-12 TWO-WATTMETER METHOD . 57 4-13 THREE WATTMETER METHOD 57 4-14 THREE WATTMETER METHO
44、D, USING ARTIFICIAL NEUTRAL . 58 4-15 FORM-FACTOR PLOT TO REDUCE EXCITATION CURRENT TO SINE-WAVE BASIS (IsFs) . 59 4-16 SINGLE-PHASE TRANSFORMER CONNECTION FOR IMPEDANCE-LOSS AND IMPEDANCE VOLTAGE TESTS 62 4-17 CONNECTIONS FOR IMPEDANCE-LOSS AND IMPEDANCE-VOLTAGE TESTS OF AN AUTOTRANSFORMER 63 4-18
45、GENERAL IMPEDANCE BRIDGE NETWORK 66 4-19 POTENTIOMETER-TYPE NETWORKS USING A PHASE SHIFTER . 66 4-20 POTENTIOMETER-TYPE NETWORK USING A MUTUAL INDUCTOR . 67 4-21 CONNECTIONS FOR THE VOLTMETER-AMMETER METHOD OF RESISTANCE MEASUREMENT 72 4-22 TEMPERATURE RISE OF SINGLE-PHASE TRANSFORMERS BY THE LOADIN
46、G-BACK METHOD . 75 4-23 TEMPERATURE RISE TEST OF THREE-PHASE TRANSFORMERS BY THE LOADING-BACK METHOD . 76 4-24 TEMPERATURE RISE TESTS OF THREE-PHASE TRANSFORMERS OR THREE SINGLE- PHASE TRANSFORMERS BY THE IMPEDANCE kVA METHOD . 77 5-1 DELTA CIRCUIT WITH ONE CORNER GROUNDED . 87 5-2 DELTA CIRCUIT WIT
47、H THE MIDPOINT OF ONE PHASE GROUNDED . 87 5-3 ANGULAR DISPLACEMENT AND CONNECTIONS - SINGLE-PHASE TRANSFORMERS CONNECTED DELTA-DELTA AND Y-Y IN THREE-PHASE BANKS WITH 0-DEGREE ANGULAR DISPLACEMENT . 88 5-4 ANGULAR DISPLACEMENT AND CONNECTIONS - SINGLE-PHASE TRANSFORMERS CONNECTIONED DELTA-Y AND Y-DE
48、LTA IN THREE-PHASE BANKS WITH 30-DEGREE ANGULAR DISPLACEMENT . 88 5-5 0-DEGREE PHASE DISPLACEMENT DELTA-DELTA OR Y-Y 89 5-6 30-DEGREEE PHASE DISPLACEMENT DELTA-Y OR Y-DELTA 89 5-7 90-DEGREE PHASE DISPLACEMENT . 90 5-8 90-DEGREE PHASE DISPLACEMENT, COUNTER-CLOCKWISE ROTATION 90 ST 20-2014 Page vii 20
49、14 National Electrical Manufacturers Association Foreword This foreword is not part of NEMA ST 20 Dry-Type Transformers for General Applications. This standard references applicable ANSI and other national standards. This update maintains or incorporates applicable sections of documents in the Reference Section to provide a “one source” technical requirement standard. This standard incorporates sound level requirements. NEMA standards publications are subject to periodic review. They are revised frequently to reflect user input and to meet changing
