In
electrical power transmission, a transposition tower is a
transmission tower
A transmission tower, also known as an electricity pylon or simply a pylon in British English and as a hydro tower in Canadian English, is a tall structure, usually a steel lattice tower, used to support an overhead power line.
In electrical ...
that changes the relative physical positions of the
conductors of a
transmission line
In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmi ...
in a
Polyphase system
A polyphase system is a means of distributing alternating-current (AC) electrical power where the power transfer is constant during each electrical cycle. AC phase refers to the phase offset value (in degrees) between AC in multiple conducting ...
. A transposition tower allows these sections to be connected together, while maintaining adequate clearance for the conductors. This is important since it distributes
electrical impedance
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit.
Quantitatively, the impedance of a two-terminal circuit element is the ratio of the com ...
s between phases of a circuit over time, reducing the problem of one conductor carrying more current than others.
Double-circuit lines are usually set up with conductors of the same phase placed opposite each other.
This reduces the reactance due to mutual inductance; the reactance of both circuits together is less than half that of one circuit. For example, a section of a line may be (top-to-bottom) phases A-B-C on the left, also phases C'-B'-A' on the right. The next section may be B-C-A on the left, also A'-C'-B' on the right. Therefore, the rotation on each side of the tower will be opposite.
Verdrillmast_Oberwoehr.jpg, Here, on the right the phases are rotated; on the left, two phases are swapped, thus the rotation sense changed.
Facility4508_Pylon206.JPG, Transposition tower. On the right side, the phases are rotated upward, on the left side downward.
Tannenbaum_pylon3_poland.jpg, Transposition by using elongated traverses
380_kV_çaprazlama_-_panoramio.jpg, Transposition on a single-phase line
View of transposition towers on MWD 1 northeast of Mead Substation, view north-northeast - Hoover Dam, Metropolitan Water District Line 1, U.S. Highway 93, Boulder City, Clark County, HAER NV-27-P-8.tif, Transposition by using multiple towers
Verdrillung im Spannfeld noerdlich Malmoe2002.png, Transposition in the span field of a 420 kV-line in Sweden
See also
*
Transposition (telecommunications)
*
Suspension tower
In an electric power transmission line, a suspension tower is where the conductors are simply suspended from the tower, the mechanical tension being the same on each side.
In this case, the tower is supposed to carry a downward force, and a later ...
*
Dead-end tower
References
External links
{{Commonscat, Transposition towers
Overhead power lines
Electric power transmission