Editing Dead-end tower (section)

{{Short description|Structure used in construction of overhead power lines}}
{{More citations needed|date=May 2010}}

[[File:Electricity pylons 330kV in Ukraine.jpg|thumb|upright|Dead-end ("anchor") towers]]
A '''dead-end tower''' (also '''anchor tower''', '''anchor pylon''')<ref name="Gemmill1920">{{cite book |url=https://archive.org/details/transmissiontow00gemmgoog |page=[https://archive.org/details/transmissiontow00gemmgoog/page/n50 48] |quote=anchor transmission tower. |title=Transmission towers |accessdate=2010-05-15 |publisher=Blaw-Knox |author=Edwin Le Roy Gemmill |year=1920}}</ref> is a fully self-supporting structure used in construction of [[overhead power line]]s. A dead-end [[transmission tower]] uses horizontal [[strain insulator]]s at the end of conductors. Dead-end towers may be used at a [[electrical substation|substation]] as a transition to a "slack span" entering the equipment, when the circuit changes to a [[Undergrounding|buried cable]], when a transmission line changes direction by more than a few degrees, or at intervals along a straight run to limit the extent of a catastrophic collapse. 
[[File:Electric substation.jpg|thumb|upright|Strain pylons and an [[anchor portal|anchor gantry]]]]
Since dead-end towers require more material and are heavier and costlier than suspension towers, it is uneconomic to build a line with only self-supporting structures.<ref>D.G. Fink, H.W. Beaty, ''Standard Handbook for Electrical Engineers Eleventh Edition'', McGraw-Hill, 1978 {{ISBN|0-07-020974-X}}, pp. 14-80, 14-81</ref>

Dead-end towers are used at regular intervals in a long transmission line to limit the cascading tower failures that might occur after a conductor failure.  An in-line dead-end tower will have two sets of strain insulators supporting the lines in either direction, with the lines connected by a jumper between the two segments. Dead-end towers can resist unbalanced forces due to line weight and tension, contrasted with [[suspension tower]]s which mostly just support the conductor weight and have relatively low capacity for unbalanced load. Dead-end towers may use [[earth anchor]] cables to compensate for the [[symmetry|asymmetric]] attachment of the conductors. They are often used when the power line must cross a large gap, such as a [[railway]] line, [[river]], or [[valley]].
[[File:NIGU_Strain_tower.JPG|thumb|Strain tower on transpower's 400xkV whakamaru to brown hill road transmission line.]]
[[File:Abspannmast_Abspannportal.jpg|thumb|Tension tower (also called strain or dead end pylon]]

Dead-end towers may be constructed of the same materials as other structures of the line.  They may be steel or aluminum lattice structures, tubular steel, concrete, or wood poles.