IEEE 1299-1996 pdf download IEEE Guide for the Connection of Surge Arresters to Protect Insulated, Shielded Electric Power Cable Systems
1. Overview
1.1 Scope
This guide suggests surge arrester installation methods at distribution cable terminal poles in order to minimize the total impressed transient voltage on medium-voltage distribution cables. Grounding electrode techniques, pole ground values, and system ground grid values are not addressed or considered in this document
1.2 Purpose
Historical surge arrester installation techniques for cable system protection may not have provided requiredmargins of protection. Variables include the terminal-pole arrester characteristics, connection lead lengthinductive voltage drop and cable system open and mid-point arrester utilization. Different protectionschemes are presented to assist the user who is designing overvoltage protection for cable systems to estimate available margins of protection. Margin of protection calculation cases for simple cases, which do notconsider multiple reflections or the effects or cable taps, are included as practical examples in Annex A
2.Cable damage
Medium-voltage cables are connected to overhead distribution lines and subjected to surge conditions. Overvoltage may contribute to failure or reduction in cable life B7l, B8). It is apparent cable life may beextended with improved surge protection (B7],(B8], B9]. Significant aspects of cable surge protectioninclude
0Appropriate arrester at the terminal pole.
Minimum connection lead length.
Determination of the system BIL, with possible derating for aged systems, and
dUse of open point and midpoint arresters, as necessary, to maintain desired margins of protection.
3. Lightning overvoltage and cable system effects
3.1 Lightning surges on the overhead distribution system
Medium voltage cables can be subjected to severe transient overvoltages as a result of lightning striking on,or near the overhead distribution system to which the cable is connected, Lightning strokes terminating onthe overhead distribution line are called direct strokes. Strokes to ground, or to other objects such as trees orstructures, in the vicinity of the overhead line produce electromagnetic fields that can induce substantialovervoltages. These strokes. which do not strike the line but are sufficiently close to induce overvoltages. arecalled induced strokes.
3.1.1 Direct strokes
For a direct stroke, the voltage on the overhead line is the product of the line surge impedance and the strokecurrent magnitude. The surge impedance of a typical distribution line is approximately 400 02. Unless thestroke is to an open end of a line, the surge current can propagate in both directions away from the strokelocation. Therefore the stroke current is divided in two. and the line voltage is
Because lightning stroke crest currents are on the order of tens of kiloamperes, crest line voltage for a direct stroke is on the order of megavolts. This voltage level greatly exceeds typical distribution line insulation lev- els, and line ashover usually results. An exception is when the line is protected by an arrester within a short distance from the stroke location.
IEEE 1299-1996 pdf download
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