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This is a reproduction of a library book that was digitized by Google as part of an ongoing effort to preserve the information in books and make it universally accessible. https://books.google.com Solenoids,electromagnetsandelectro-magneticwindings... CharlesReginaldUnderhill .<rw\ , M tit nc>o SOLENOIDS ELECTROMAGNETS AND ELECTROMAGNETIC WINDINGS BY CHARLES R: UNDERHILL CONSULTINg ELECTRICaL ENgINEER aSSOCIaTE MEMBER aMERICaN INSTITUTE OF ELECTRICaL ENgINEERS 223 ILLUSTRATIONS NEW YORK D. VAN NOSTRAND COMPANY 1910 COPYRIGHT, 1910, BY D. VAN NOSTRAND COMPANY. PREFACE Since nearly all of the phenomena met with in elec trical engineering in connection with the relations between electricity and magnetism are involved in the action of electromagnets, it is readily recognized that a careful study of this branch of design is necessary in order to predetermine any specific action. With the rapid development of remote electrical con trol, and kindred electro-mechanical devices wherein the electromagnet is the basis of the system, the want of accurate data regarding the design of electromagnets has long been felt. With a view to expanding the knowledge regarding the action of solenoids and electromagnets, the author made numerous tests covering a long period, by means of which data he has deduced laws, some of which have been published in the form of articles which appeared in the technical journals. In this volume the author has endeavored to describe the evolution of the solenoid and various other types of electromagnets in as perfectly connected a manner as possible. In view of the meager data hitherto obtainable it is believed that this book will be welcomed, not only by the electrical profession in general, but by the manu facturer of electrical apparatus as well. iii iv PREFACE The thanks of the author are due to Mr. W. D. Weaver, editor of Electrical World, for his permission to reprint articles, forming the basis of this work, originally published in that journal, and also for his friendly cooperation and encouragement. The labors of Professor Sylvanus P. Thompson in this field deserve recognition from the electrical profession, to which the author desires to add his personal acknowledgments. The author,s thanks are also due to the many friends to whose friendship he is indebted for the facilities afforded him to make the tests referred to in this volume. To Mr. Townsend Wolcott the author is indebted for his valuable assistance in correcting errors and for many suggestions. CHARLES R. UNDERHILL. New York, June, 1910. CONTENTS CHAPTER I Introductory aRT. "O" 1. Definitions 1 2. The C. G. S. System of Units 2 3. General Relations between Common Systems of Units . 3 4. Notation in Powers of Ten 7 CHAPTER II Magnetism and Permanent Magnets 5. Magnetism 8 6. Magnetic Field 9 7. Permanent Magnets ........ 10 8. Magnetic Poles 12 9. Forms of Permanent Magnets 13 10. Magnetic Induction 15 11. Magnetic Units 15 CHAPTER III Electric Circuit 12. Units 17 13. Circuits 20 CHAPTER IV Electromagnetic Calculations 14. Electromagnetism 24 15. Force surrounding Current in a Wire .... 24 16. Attraction and Repulsion 25 17. Force due to Current in a Circle of Wire ... 26 v vi CONTENTS aRT. PaGE 18. Ampere-turns 27 19. The Electromagnet 27 20. Effect of Permeability 28 21. Saturation 29 22. Saturation expressed in Per Cent 31 23. Law of Magnetic Circuit 32 24. Practical Calculation of Magnetic Circuit ... 34 25. Magnetic Leakage 36 CHAPTER V The Solenoid 26. Definition 40 27. Force due to Single Turn 42 28. Force due to Several Turns One Centimeter Apart . 45 29. Force due to Several Turns placed over One Another . 49 30. Force due to Several Disks placed Side by Side . 51 31. Force at Center of any Winding of Square Cross-section 54 32. Tests of Rim and Disk Solenoids 54 33. Magnetic Field of Practical Solenoids .... 61 34. Ratio of Length to Average Radius .... 65 CHAPTER VI Practical Solenoids 35. Tests of Practical Solenoids 69 36. Calculation of Maximum Pull due to Solenoids . 75 37. Ampere-turns required to saturate Plunger ... 79 38. Relation between Dimensions of Coil and Plunger . 82 39. Relation of Pull to Position of Plunger in Solenoid . 85 40. Calculation of the Pull Curve 93 41. Pointed or Coned Plungers 98 42. Stopped Solenoids 99 CHAPTER Vn Iron-clad Solenoid 13. Effect of Iron Return Circuit 102 44. Characteristics of Iron-clad Solenoids .... 103 CONTENTS vii AKT. PAGB 45. Calculation of Pull 104 46. Effective Range 105 47. Precautions 108 CHAPTER VIII Plunger Electromagnets 48. Predominating Pull 110 49. Characteristics 110 50. Calculation of Pull Ill 51. Effect of Iron Frame 112 52. Most Economical Conditions 113 53. Position of Maximum Pull 119 54. Coned Plungers 120 55. Test of a Valve Magnet 125 56. Common Types of Plunger Electromagnets . 129 57. Pushing Plunger Electromagnet 130 58. Collar on Plunger 130 CHAPTER IX Electromagnets with External Armatures 59. Effect of placing Armature Outside of Winding . 131 60. Bar Electromagnet 132 61. Ring Electromagnet 133 62. Horseshoe Electromagnet 133 63. Test of Horseshoe Electromagnet 134 64. Iron-clad Electromagnet 136 65. Lifting Magnets 137 66. Calculation of Attraction 142 67. Polarity of Electromagnets 144 68. Polarized Electromagnets 144 CHAPTER X Electromagnetic Phenomena 69. Induction 148 70. Self-induction 149 viii CONTENTS aRT. TaGK 71. Time-constant 150 72. Inductance of a Solenoid of Any Number of Layers . 152 73. Eddy Currents 153 CHAPTER XI Alternating Currents 74. Sine Curve 154 75. Pressures 155 76. Resistance, Reactance, and Impedance .... 160 77. Capacity and Impedance 160 78. Resonance 161 79. Polyphase Systems 164 80. Hysteresis 165 CHAPTER XII Alternating-current Electromagnets 81. Effect of Inductance 168 82. Inductive Effect of A. C. Electromagnet .... 170 83. Construction of A. C. Iron-clad Solenoids . 171 84. A. C. Plunger Electromagnets 172 85. Horseshoe Type 174 86. A. C. Electromagnet Calculations 175 87. Polyphase Electromagnets 176 CHAPTER XIII Quick-acting Electromagnets, and Methods of Reducing Sparking 88. Rapid Action 184 89. Slow Action 184 90. Methods of reducing Sparking 185 91. Methods of preventing Sticking 189 CHAPTER XIV Materials, Bobbins, and Terminals 92. Ferric Materials 191 93. Annealing 192 CONTENTS ix AKT. PAGE 94. Hard Rubber 192 95. Vulcanized Fiber 193 96. Forms of Bobbins 194 97. Terminals 197 CHAPTER XV Insulation of Coils 98. General Insulation 201 99. Internal Insulation 201 100. External Insulation 204 CHAPTER XVI Magnet Wire 101. Material 210 102. Specific Resistance 210 103. Manufacture . 211 104. Stranded Conductor 211 105. Notation used in Calculations for Bare Wires . 211 106. Weight of Copper Wire 212 107. Relations between Weight, Length, and Resistance . 212 108. The Determination of Copper Constants . 213 109. American Wire Gauge (B. & S.) 215 110. Wire Tables 215 111. Square or Rectangular Wire or Ribbon .... 217 112. Resistance Wires 218 CHAPTER XVII Insulated Wires 113. The Insulation 220 114. Insulating Materials in Common Use .... 220 115. Methods of insulating Wires 221 116. Temperature-resisting Qualities of Insulation . 222 117. Thickness of Insulation ....... 225 118. Notation for Insulated Wires 226 119. Ratio of Conductor to Insulation in Insulated Wires . 227 120. Insulation Thickness 228 X CONTENTS CHAPTER XVIII Electromagnetic Windings ABt. PAGE 121. Most Efficient Winding 229 122. Imbedding of Layers 232 123. Loss at Faces of Winding 234 124. Loss Due to Pitch of Turns 234 125. Activity 237 126. Ampere-turns and Activity 239 127. Watts and Activity 239 128. Volts per Turn 240 129. Volts per Layer 241 130. Activity Equivalent to Conductivity .... 242 131. Relations between Inner and Outer Dimensions of Winding, and Turns, Ampere-turns, etc. 245 132. Importance of High Value for Activity .... 245 133. Approximate Rule for Resistance 246 134. Practical Method of Calculating Ampere-turns . 246 135. Ampere-turns per Volt 248 136. Relation between Watts and Ampere-turns . 248 137. Constant Ratio between Watts and Ampere-turns, Volt age Variable 250 138. Length of Wire 251 139. Resistance calculated from Length of Wire . 251 140. Resistance calculated from Volume .... 252 141. Resistance calculated from Turns 253 142. Exact Diameter of Wire for Required Ampere-turns . 254 143. Weight of Bare Wire in a Winding .... 254 144. Weight of Insulated Wire in a Winding . 255 145. Resistance calculated from Weight of Insulated Wire . 255 146. Diameter of Wire for a Given Resistance . 256 147. Insulation for a Given Resistance 256 CHAPTER XIX Forms of Windings and Special Types 148. Circular Windings 257 149. Windings on Square or Rectangular Cores . 260 CONTENTS xi aBT. PaGE 150. Windings on Cores whose Cross-sections are between Round and Square 263 151. Other Forms of Windings 269 152. Fixed Resistance and Turns 269 153. Tension 270 154. Squeezing 271 155. Insulated Wire Windings with Paper between the Layers 272 156. Disk Winding 273 157. Continuous Ribbon Winding 273 158. Multiple Wire Windings 274 159. Differential Winding . 274 160. One Coil wound directly over the Other . 275 161. Winding consisting of Two Sizes of Copper Wire in Series 275 162. Resistance Coils 277 163. Multiple-coil Windings 277 164. Relation between One Coil of Large Diameter, and Two Coils of Smaller Diameter, Same Amount of Insu lated Wire, with Same Diameter and Length of Core in Each Case .... 284 165. Different Sizes of Windings connected in Series . 285 166. Series and Parallel Connections 286 167. Winding in Series with Resistance .... 287 168. Effect of Polarizing Battery 294 169. General Precautions 295 CHAPTER XX Heating of Electromagnetic Windings 170. Heat Units 296 171. Specific Heat .296 172. Thermometer Scales 297 173. Heating Effect 298 174. Temperature Coefficient 299 175. Heat Tests 302 176. Activity and Heating 302 xii CONTENTS CHAPTER XXI Tables and Charts PaGE Standard Copper Wire Table 305 Metric Wire Table 306 Approximate Equivalent Cross-sections of Wires .
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