IEEE Std 1692 pdf free download

IEEE Std 1692 pdf free download.Protection of Commu nication Instal lations from Lightning Effects.
5.3 Lightning—a major source of ground potential rise
There is a 50% probability that a lightning strike will be approximately 30 kA (see Anderson and Eriksson 0). If the self-inductance of the earth is estimated very conservatively to be 0.5x1061l, and considering that lightning takes the form of a pulse which has a typical rise time of2xlO4s, then using V = Ldildt yields the estimated GPR of a 30 kA strike to be 7.5 kV. I ligher current lightning strikes or strikes passing through higher inductance ill yield higher values of GPR.
If the inductance of a grounding system is estimated to be lxl0’ II, then the GPR resulting from a 30 kA lightning strike will be around 15 kV. Any grounded equipment that is connected to wire-line communication pairs will then be in jeopardy from outgoing currents seeking a path to remote earth.
In large structures having a large number (1000+) of communication pairs, such as a telecommunications central ofike. the GPR effect will be greatly reduced due to the current division in the many multiple paths (the communication pairs) to remote earth. however, for small structures with relatively few communication pairs. all the available grounding paths must be considered including wire-line, multigrounded neutral (MGN). water pipes, building steel. etc. Structures connected to large metallic infrastructure may have lower GPR values. For smaller structures, the isolation decision depends on many considerations including equipment characteristics, type of services, and location.
6. Handling lightning strike current
Controlling the dissipation path for lightning strike current requires current redirection through a combination of current division and current blocking techniques. This approach is an absolute must for success, because of the magnitude of the current, the resulting surge impedance of any single dissipation path and the availability of secondary fault current paths through the electronics equipment. Multiple connections (minimum 4 but 10 preferred) between the tower and a grounding ring will divide lightning current into smaller segments. This division will ensure that the lightning surges will follow the designated paths tbr dissipation into the earth and thus lower the resulting GPR to the adjacent equipment building grounding system.
Fault current blocking through automatic ac disconnect isolation requires protected equipment to have power back-up systems such as battery, uninterruptible power supply, or battery/generator equipment for uninterrupted operation during ac isolation. AC service is automatically reconnected after the threat has subsided below an acceptable threshold.
AC isolation periods for LGPR will nominally be several minutes but are automatically extended if the LGPR threat condition persists. Isolation periods for power line fault conditions will be several seconds. but also extend if power line conditions do not return to acceptable levels. AC isolation will respond to power line sags. swells, and short term transients exceeding threshold levels.
Effective ac disconnect isolation requires preemptive detection of impending LGPR events. Detection of LGPR from approaching storms and of rapidly changing local surface electric tields provides the indications of imminent threat.
There is no means to predict power-related fault conditions. AC isolation will minimize the stress caused by extended poor ac power quality. AC power is reconnected to the protected equipment after it stabilizes within selected thresholds. As a result, the site is not exposed to power recovery transients following a power service failure.IEEE Std 1692 pdf download.