Issue link: https://www.e-digitaleditions.com/i/1156106
40 I ICT TODAY However, as the telecom industry learned many years ago, the aluminum shielding material is ineffective in reducing lower-frequency (i.e., fundamental frequency of the power system at either 50 or 60 Hz and lower) induction of the magnitude that can cause equipment malfunctions and damages from lightning or power- induced surges. Of course, no amount of shielding can prevent the occurrence of GPR conditions. Shielding effectiveness at low frequencies increases with the use of ferromagnetic materials, such as steel, which have much higher permeability or magnetic flux densities than non-ferromagnetic materials, such as aluminum and copper. This fact is well documented in Shielding of Ground-Return Circuits at Low Frequencies in Engineering Report #26, which was prepared in 1934 by the Joint Subcommittee for Development and Re- search of the Edison Electric Institute and the Bell Telephone System. The most significant part of the report is in the Effect of Added Mutual Impedance section (page 11, paragraph 2.6). It states that "any addition to the self-impedance of the shielding circuit, which at the same time is added to the disturbing or disturbed circuit, diminishes the shield factor, and if the added impedance is large, the shielding can be made almost perfect. One application of this principle is through the insertion at intervals of mutual inductance coils, so-called 'neutralizing transformers.'" Thus, shielding theory works in the same way as a neutralizing transformer and vice versa. If one under- stands how a neutralizing transformer works, it is under- stood why aluminum or copper shielded cable is inef- fective in canceling or neutralizing low-frequency induced voltages. FIGURE 8: Before and after induced lightning surge impulses with a DSL INT prototype. A BREAKTHROUGH COMPUTER NETWORKING TECHNOLOGY IS THE SOLUTION! On September 4, 2007, AT&T (based on the work of this author) received the first of three U.S. patents on a Digital Subscriber Line Induction Neutralizing Transformer Network. The main idea was to redesign the commercially avail- able induction neutralizing transformer (INT) for use on xDSL-type circuits to overcome an inherent design problem that could potentially create crosstalk inter- ference issues. Instead of having the INT wound with Cat 3 cable, as the standard and digital carrier units are, Cat 5 or Cat 6 cable would be used to minimize this issue. The design objective was also to obtain a smaller, less expensive unit that was more efficient in suppressing high-frequency impulse noise interference levels. In December 2009, a prototype DSL INT unit was built with Cat 5 UTP, and it was shown to effectively suppress 98 percent of the low-frequency induced voltage on a telephone circuit, along with achieving substantial To ensure that cabling facilities can successfully handle high-performance video streaming demands, the LAN is expected to function like a utility-grade infrastructure or (UTG).