Abstract
Several miles of a main conduit route in a metropolitan area containing bare lead sheath telephone cables has been protected satisfactorily from stray current corrosion by a single 700,000 cm drainage wire. During and following the war period there was a rapid expansion of all types of underground utilities throughout the area. This altered the subsurface network conditions, causing the efficiency of the former protection to be greatly diminished.
Investigation indicated that in order to reestablish adequate protection by a single natural drainage connection, a much larger wire would be required. Further investigation indicated that by utilizing natural drainage from two points on the conduit system, thus providing the equivalent of distributed drainage, the size of wire for a natural drainage connection could be reduced appreciably.
As the result of additional study it was decided to utilize a controlled type of rectifier employing two stages of magnetic amplification. The primary purposes of such equipment were to overcome the IR drop in the drainage conductor and to limit the drainage current to the minimum value required by the natural potential difference between cable and earth. Employment of this equipment permitted the use of a distributed drainage arrangement, utilizing the original drainage facilities for one branch and a much smaller wire for the second branch.
This paper describes the system in detail, discusses the results obtained and the problems encountered in adjusting the rectifier equipment to obtain the desired operating characteristics. 5.2.1
