  # Electrical Losses in the Gun Coils

(Reproduced from "Zero to Eighty" pp.303 by EF Northrup)

Due to the electrical resistance of the coil conductors, a certain amount of energy is dissipated as heat in I2R loss. However, by energizing only a comparatively short section of the gun at a time, a great saving in power can be made over that which would be wasted in overcoming the electrical resistance of the whole 1000 meters of coil. By a suitable power shifting scheme described briefly hereinafter (page 274), only about a fifteen meter length need be carrying current.

Supposing enough coils were energized to provide fifteen consecutive waves of which two were behind the projectile, about five coincident with the main body of the projectile, and the remainder ahead of the projectile, then we would have ninety separate phase coils through which we would have to pass about 4000 amperes. Experimental data show that the 2000 cycle resistance of the size of conductor selected is approximately 15 × 10-4 ohm per meter. Each phase coil has about 15.5 meters of tubing. The electrical resistance of each unit phase coil is thus 0.023 ohm. At 4000 amperes, the I2R loss per phase coil is 40002 × 0.023 = 370,000 watts or 370 kilowatts. The use of ninety phase coils would set the total coil loss at approximately 33,000 kilowatts. As the power would be on for only two seconds, the total energy expended in coil loss would be 18.3 kilowatt-hours.

The approximate weight of copper tubing in the gun is something like 57,000 kilograms. The specific heat of copper is about 0.09 calorie per gram. From the total electrical energy expended in copper loss, and the weight of the copper, we find that the temperature rise of the coil is only 0.0031° C.

 < Previous Page 6 of 17 Next >