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The Attenuation of Radio-Frequency Disturbance High-Voltage Transmission Lines

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Ocrs*qsttt&rn runL rr *ttcuugtlas eyetru slsral-{ br sromnlca}" Alatroct* flS**t I lhptrrf s Sh*sLr &lria $. fiafo[], THE ATTENUATION OF RADIO -FREQUENCY DISTURBANCE Oil HIGH-VOLTAGE T.RANffi~SSION LINES by MELVIN JULIUS KOFOID A THESIS submitted to the OREGON STATE AGRICULTUP~ COLLEGE / in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE June 1935 AIPBOTED: Redacted for Privacy r* d Researoh Professor of &Lectrleal Englneerln6 A. ,\ In Charge of MaJor l Redacted for Privacy n n {- .\ Eead of Deperfuent of Slectrlca1 Englueering sb q a Redacted for Privacy ,l t- rl f Cbalrmau of $obool Graduate Connlttee a\ b- Redacted for Privacy Chalrmao of Colle Oraduat e Counoll ACKNO V~EDGEMENT The author wishes to give full credit to ~rofessor F. o. McMillan for the original suggestion of the possible use of.a filter circuit, utilizing the insulators as capacitors, on a high-voltage transmission line to attenuate the transmission of radio frequency interference. The encouragement and continued assistance and suggestions given by ~rofessors F. o. McMillan, A. L. Albert, and E. C. Starr of the Electrical Engineering Department of Oregon State College is very gratefully acknowledged. The laboratory investigation was made possible by the financial support and laboratory facilit~s furnished by the Oregon State College Engineering Experiment Station and Electrical Engineering Department. TABL · List of Illustrations. I. INTRODUCTION. The Problem of Radio-FreQ:uency Interference from High-Voltage Transmission Lines 1 Some Previous Contributions to the Elimination of Radio-Frequency Interference 3 Limitations of Present Methods of Radio­ ~requency Inter·ference Attenuation 3 II. RADI0-~3~ UENCY FIL~~~ S~CTIONS FOR HIGH­ VOLT G • T£U.l S ...I SION LIHES. Field of Application 5 Frequency Range of Attenuation 5 Plan of Filter Section Construction 6 III. FILTER S~CTION D.clSIGN D THEO ETICAL CHA.F.ACTERISTICS. Desired Impedance Characteristics 8 Theoretical Impedance Characteristics of 8 Tenative Section Number of Filter Circuits in Section 10 Distribution of Resonant Frequencies of ~ilter Circuits in a ~ilter ection 10 IV . FILTER CIRCUIT CAPACITO,S. Dielectrics of High-Voltage Insulators ll Capacitanceu of High-Voltage Insulators ll V. FILTER CIRCUIT I JDUC TANCES. Inductance equireuents 14 Practical and Economical Considerations 14 TABLE 0~, CONTENTS (Continued) Electrical Considerations 14 Inductance Calculations and Coil Design 16 VI. LABO TORY DETEIDviii~ATION OF FILTER CIRCUIT AND FILTER SECTION CHARACTERISTICS. Test Inductances and Insulators 18 Test Circuits, Apparatus, and Armangements 18 Testing Procedure 20 VII. EXPERIMENTAL FILTER CIRCUIT AND FILTER SECTION CHAR CTERI STI CS. Impedance Char acteristics of Insulators Alone 22 Impedance Char ac te:ristics of Individual Filter Cir·cu its 22 Impedance Char acteristics of l'art of a Comple te Filter Section 23 VIII. FILTER SECTION INSTALLATION ON A THRE~l'HASE TRANSMISSION LINE. Arrangement of Coils Throughout Section 26 Installation of Coils .26 Adjustment of Inducta nce of Coils 27 IX. CONCLUSIONS. 28 :X:. BIBLIOGRAPHY. 30 LIST OF ILLUS TRATIONS Fig. 1 Installation of Inductances on a High-Volt~ge Transmission Line for Attenuating Radio-~requency Disturbance. Fig. 2 A fheoretical Admittance Diagram of a Radio­ Frequency Filter Circuit on a High-Voltage Transmission Line. Fig. 3 Photographs of Lab oratory Arrangements for Obtaining Impedance Characteristics of Radio­ Frequency Filter Circuits and Sections. Fig. 4 Circuit Diagram for Obta ingng Impeda nce Characteristics of Radio-Frequency Filter Circuits. Fig . 5 Head to Pin Impe dance of 66 Kv. Reffrey-Dewitt iJO. 94 Insulators. Fig . 6 Line to Ground Impeda nce of Radio-Frequency Series Fil te:r Circuits . Fig. 7 Line to Gr-ound I mpedance of Radio-Frequency Series Filter Circuits. Fig. 8 Line to Ground I mpedance of Three Radio­ :IPrequency Series Filter Circuits in :Parallel. Fig. 9 Line to Ground Impedance of Three Radio­ Frequency Series Filter Circ~uts in Parallel. Fig. 10 Typical Installation of Attenuation Coils oh a Wood :Pole of a Three-Phase Transmission Line.­ ~ ATTENUATION Q! RADIO FREQUENCY DISTURBAl~CE .....ON. ~ VOLTAGE !:RANSMISSION LINES INTRODUCTION The Problem of Radio Frequency Interference from High Voltage Transmission Lines: A high-voltage transmission line causes interference in radio receivers because of the electromagnetic radiation resulting from distur~ances on the conductors or associated equipment. The magnetic and dielectric fields of this radiation are between conductors and between conductors and ground, the major portion of the interference caused in radio receivers being due to the fields between conductors and ground. A common source of electrical disturvances of radio frequencies from high-voltage transmission lines is the ionization and break-down of over-stressed air in the pin hole of the insulator, and between the conductor, tie wire, and insulator head. In some cases interference is caused by leakage currents flowing through conducting deposits of various kinds on the insulator surface. Other sources of interference are poor connections, loose tie wires, loose hardware, and defective equipment. 2 The most evident problem that presents itself is that of the elimination of the source of the disturvances as completely as possible. High class line construction and maintenance is necessarily rather expensive, and while essential for the complete elimination of sources of inter­ ference in urban areas, its use throughout, on long power lines traversing sparcely inhabited districts between the plant and the load center in many oases is not economically • justified. The additional expense of constructing a new line so that it would be free from radio frequency inter­ ferenoe causing disturbances may not be great since insulators quite free from radio interference are now available, but the riddance of disturvanoe from a complete line already installed generally would involve an expense that would be prohibitive. While high frequency disturbances on a line in lightly populated areas is not of serious consequence in such areas, such disturbances will travel along the transmission line for lo~g distances with remarkably small attenuation, into what may be othercise disturbance-free sections.
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