Harmonic Characteristics of Rectifier Substations and Their Impact on Audio Frequency Track Circuits
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U M T A-M A-06-0025-81-6 DOT-TSC-UMTA-81 -75 Harmonic Characteristics of Rectifier Substations and Their Impact on Audio Frequency Track Circuits Vilas D. Nene 0A0 Corporation 7500 Greenway Center Greenbelt MD 20770 May 1982 Final Report This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161. U.S. Department of Transportation Urban Mass Transportation Administration Office of Technical Assistance Office of Systems Engineering Washington DC 20590 NOTICE This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. NOTICE The United States Government does not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of this report. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. UMTA-MA-06-0025-81-6 4. Title and Subtitle 5.May Report 1982 Date andHarmonic Their CharacteristicsImpact on Audio of Frequency Rectifier Track Substations Circuits 6.DTS-722 Performing Orgonizotion Code 8. Performing Organization Report No. Vilas7. Authors) D. Nene, Ph.D. DOT-TSC-UMTA-81-75 0A09, Performing Corporation* Organization Name and Address 10.UM204/R2616 Work Unit No. (TRAIS) 7500 Greenway Center 11. Contract or Grant No. Greenbelt, Maryland 20770 DTRS-57-81-C-00033 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Final Report U.S. Department of Transportation 1/15/1981 - 7/15/1981 Urban Mass Transportation Administration Office of Technical Assistance 14. Sponsoring Agency Code Washington DC 20590 URT-10 is. suppiomentaryNotes u.S. Department of Transportation *Under contract to: Research and Special Programs Administration Transportation Systems Center ___________________Cambridge MA 02142 ___________________ 16. Abstract This report describes the basic operation of substation rectifier equipment and the modes of possible interference with audio frequency track circuits used for train detection, cab signalling and vehicle speed control. It also includes methods of estimating EM noise received by track circuits from substation operation. 17. Key Words 18. Distribution Statement Rectifiers, Substation Harmonics, DOCUMENT IS AVAILABLE TO THE U.S. PUBLIC Electromagnetic Interference THROUGH THE NATIONAL TECHNICAL INFORMATION SERVICE, SPRINGFIELD, VIRGINIA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) * 21* No. of Pages 22. P ric e UNCLASSIFIED UNCLASSIFIED 54 Form D O T F 1700.7 (8-72) Reproduction of completed page authorized PREFACE This report was commissioned of 0A0 Corporation under contract to the Transportation Systems Center (TSC) of the U.S. Department of Trans portation. Funding was provided under the Subsystem Technology Applications to Rail Systems (STARS) Program of the Urban Mass Transportation Administra tion (UMTA). The author wishes to thank Mr. Stephen S. Teel of the U.S. DOT/UMTA and Mr. Lennart E. Long of the U.S. DOT/TSC for their strong support of this work. iii METRIC CONVERSION FACTORS Approximata Conversion* to Metric Measures n Appioximate Convaisions Iiom Matiic Maasuras N Symbol When You Know Multiply hy To Find Symbol Symbol Whan You Know Multiply hy To find Symbol M LENGTH S LENGTH mm millimeters 0.04 inches in cm centimeters 0.4 inches in m meters 3.3 feet ft in inches *2.5 centimeters cm 00 m motors 1.1 yards yd II loot 30 centimeters cm •4 km kilometers 0.6 miles mi yd yards 0.9 meters m -------- ; mi miles 1.6 kilometers km • r - —E AREA AREA H 9t - cm2 square centimeters 0.16 square inches in3 in2 equate ind ie s 6.6 square centimeters cm2 ____ z IA m2 square meters 1.2 oquare yards yd2 It2 square feet 0.09 square meters m2 — z km2 equate kilometers 0.4 square miles mi2 yd’ square yards 0.8 square meters m2 - ■vp ha hectares (10,000 m2I 2.6 acres mi2 square miles 2.5 square kilometers km2 ____ z acres 0.4 hectares ha "~~z ce en MASS (weight) MASS (weight) - ^ § N grams 0.035 ounces ox ox ounces 28 grams g g kfl kilograms 2.2 pounds lb lb pounds 0.45 kilograms kg t tonnes (1000 kg) i . i short tons short tons 0.9 tonnes t • (2000 lb) *■' — O E *4 VOLUME - = VOLUME Ob fl ox teaspoons 5 milliliters ml ml milliliters 0.03 fluid ounces tap i.l.i. pints pt Tbsp tablespoons 16 milliliters ml CO 1 liters 2.1 id i liters 1.06 quarts qt II ox fluid ounces 30 milliliters ml ' “Z e cups 0.24 liters 1 1 liters 0.26 gallons gal cubic feet ft3 P* pints 0.47 liters 1 m3 cubic meters 35 quarts 0.96 liters 1 -* x m3 cubic meters 1.3 cubic yards yd3 q* <A gal gallons 3.8 liters 1 - It1 cubic feet 0.03 cubic meters m3 — M in yd3 cubic yards 0.76 cubic meters m3 —: TEMPERATURE (exact) — z TEMPERATURE (exact) ° c C elsius 9/5 (then Fahrenheit °F temperature add 32) tempereture ■f Fahrenheit 6/9 (after C olsius °c temperature subtracting temperature _ °F 32) °F 32 98 6 . 212 200 1 - 4 0 1 4 0 80 1 120 160 » i 4 h 1 1 p » 1 r 1 M In i 2.54 tenacity). Fur other exact conversions and more detailed tables, see N6S Misc. Pnbl. 286. f 100 Units of Weight* and Measures. Price 92.25. SO Catalog No. Cl 3.10:286. - 4 0 -20 V ~ * 20 |40 60 00 •c M ~ S ®C 37 TABLE OF CONTENTS EXECUTIVE SUMMARY vii 1. INTRODUCTION 1 2. THREE PHASE BRIDGE RECTIFIERS 2 2.1 Commutation Process 5 2.2 Output Voltage Waveform 9 2.3 Voltage Regulation 10 2.4 Operation with Unbalanced Voltage Input 10 2.5 Waveform of ac Network Current 13 2.6 Twelve Pulse Rectifier Circuits 16 2.7 A Controlled Rectifier/Inverter Circuit 21 2.8 Rectifier Substations for Transit Application 27 3. SUBSTATION HARMONICS AND TRACK CIRCUITS 28 3.1 Substation Harmonics in Propulsion Current 28 3.2 Conducted Noise 31 3.3 Noise Induced from the Third Rail 33 3.4 Assessment of Potential for Interference 37 4. CONCLUSIONS 38 APPENDIX A - RECTIFIER OPERATION WITH UNBALANCED VOLTAGE INPUT 39 APPENDIX B - REPORT OF NEW TECHNOLOGY 46 REFERENCES 48 LIST OF FIGURES FIGURE NO. TITLE PAGE NO. 2-1 Three Phase Bridge Rectifier 3 2-2 Balanced Three Phase Voltages 4 2-3 Line Current Waveforms 6 2-4 Transformer Secondary Phase Currents 6 2-5 Commutation Process 7 2-6 Variation of Harmonic Components with Overlap Angle 11 2-7 Voltage Regulation 12 2-8 Operation with Unbalanced Voltage Input 14 2-9 AC Waveform 15 2-10 Effect of Commutation on ac Network Current 17 2-11 A 12-Pulse Rectifier (Series Connection) 18 2-12 Output Voltage of 12-Pulse Circuit 20 2-13 Currents in Different Windings 22 2-14 A 12-Pulse Rectifier (Parallel Connection) 23 2-15 Operating Modes of a Controlled Rectifier 24 2- 16 Harmonic Content of a Controlled Rectifier 26 3- 1 Substation Harmonics in Propulsion Current 29 3-2 Conducted Noise in Track Circuit 32 3-3 Noise Induction by the Third Rail 34 3-4 Track Circuit Configurations 36 A-l Phasor Diagram 40 A-2 Rectifier Operation with Unbalanced Voltage Input 41 vi EXECUTIVE SUMMARY A typical transit substation has two or more diode rectifiers with a combined power rating of 2-10 MW. With a very few exceptions, these are 3- phase 12-pulse rectifier circuits. Under normal operating conditions with balanced voltage inputs, these rectifiers cause harmonic currents in the third rail with harmonic orders of multiples of 12. For example, with a source frequency of 60 Hz as in the U.S., the third rail carries current harmonics with frequencies of 720 Hz, 1440 Hz, 2160 Hz,..., etc. Because of inherent unbalance in voltage inputs as well as some asymmetry in bridge circuits, the third rail also carries current components with frequencies of 60 Hz, 120 Hz, ... etc., although of reduced magnitudes. These substation harmonics in the third rail cause electromagnetic (EM) noise in the audio frequency track circuits, resulting in potential circuit malfunction. This report describes the basic operation of substation rectifier equipment and the modes of possible interference with the track circuits. It also presents methods of estimating electromagnetic noise levels in the track circuits caused by the substation rectifiers. The substation harmonic frequencies are well defined and are independent of other wayside and vehicle equipment. The amplitudes of these harmonic currents in the third rail are highest when a train is near a feeding point on the third rail. The EM noise levels in the track circuit caused by rectifier harmonics are, however, minimum when the length of running rails in the propulsion circuit is minimum. This is because the propulsion return current is then likely to be shared equally by the two vii running rails in a two-rail circuit, and the induction from the third rail is minimum, since the length of the exposed circuit is small. Protection against substation harmonics is not necessary when rail lengths are short and currents are small except in site-specific problem areas such as the third rail switching sides at bonds, etc., or under abnormal conditions such as loose connections, etc. These problems must then be investigated on an individual basis. vi i i 1. INTRODUCTION Research and development programs of the Urban Mass Transportation Administration (UMTA) in the area of urban rail transit have been recently restructured.