ABSTRACT
Distribution cable systems have peak failure rates during the summer months throughout North America. Research work has shown that impulse surges to cables shorten their service life [1,2]. Both temperature and rainfall may peak during the same time period. All of these factors may in®uence this failure rate. It is also well documented that water trees reduce the impulse level of extruded dielectric insulated cables and contribute to the failure situation. Most of the effort that has been spent
20.1 Introduction .................................................................................................. 385 20.2 Surge Protection ........................................................................................... 386
20.2.1 Protective Margin ............................................................................. 386 20.2.2 Voltage Rating .................................................................................. 386 20.2.3 Highest Power Voltage ...................................................................... 386 20.2.4 CoefŽcient of Grounding .................................................................. 387 20.2.5 Sparkover .......................................................................................... 387 20.2.6 Surge Discharge ................................................................................ 387 20.2.7 Insulation Resistance Discharge Voltage .......................................... 387
20.3 Wave Shape and Rate of Rise ....................................................................... 387 20.4 Operation of a Surge Arrestor ...................................................................... 388
20.4.1 Air Gaps ............................................................................................ 388 20.4.2 Valve Arresters ................................................................................. 389 20.4.3 Metal Oxide Varistor (MOV) ........................................................... 389
20.5 Natural Lightning Strokes ............................................................................390 20.6 Traveling Waves ............................................................................................ 391 20.7 Velocity of Propagation ................................................................................ 392 20.8 Proper Connection of Arresters .................................................................... 393
20.8.1 Lead Lengths .................................................................................... 393 20.8.2 Route of Current Flow ...................................................................... 393 20.8.3 Ground Resistance/Impedance ......................................................... 393
References .............................................................................................................. 394
in the past on lightning protection of distribution system components has been on overhead transformers. This is logical when you consider that the companies that build transformers are also the ones that sell arresters [3].
