Dead-end tower

A dead-end tower (also anchor tower, anchor pylon) is a fully self-supporting structure used in construction of overhead power lines. A dead-end transmission tower uses horizontal strain insulators and where the conductors mechanically terminate. Dead-end towers may be used at a substation as a transition to a "slack span" entering the equipment, when the circuit changes to a buried cable, when a transmission line changes direction by more than a few degrees, or just once in a while to limit the extent of a catastrophic collapse.

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.

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 towers 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 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.

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.

Dead-end towers are also employed at branch points as branch pylons. A tower at which the power line runs further as overhead line and as underground cable is a branch tower for a cable branch.

A branch pylon is used to start a line branch. The branch pylon is responsible for holding up both the main line and the start of the branch line. This makes a branch pylon also an anchor pylon since it must resist forces from both lines.

Branch pylons frequently, but not always, have one or more cross beams transverse to the direction of travel of the line for the admission of the branching electric circuits; some also have cross beams of the branching electric circuits lying in the direction of travel of the main line. Branch pylons without additional cross beams are occasionally constructed.

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