An Investigation of Temperature and Wind Impact on ACSR Transmission Line Sag and Tension

Power transmission is mainly based on overhead transmission lines with conductors being supported by transmission towers. Transmission lines are subjected to environmental stress (temperature changes, winds, snow etc), have an impact on the surrounding areas (visual pollution, building restrictions) and experience heavy losses due to resistive, magnetic and capacitive effects. Thus, proper modeling and installation of these conductors are necessary. The conductors are generally installed in a catenary shape to minimize the capacitive effects and to balance the tension. This paper presents an investigation on the sag and tension behavior under different temperature and wind of ACSR (Aluminum Conductor-Steel Reinforced) lines. Four different cases of temperature and wind are tested to calculate sag and tension. Simulation setup is done in ETAP (electrical transient and analysis program). Results are recorded and discussed. Keywords-ACSR; overhead; line; transmission; conductors; span; sag; temperature; variation


INTRODUCTION
Overhead transmission lines are used to carry electrical power over long distances [1].The performance of these transmission lines depends on their well-engineered modeling which is one of the major issues issue during the design stage.[2].If the support structures are at the same height (which is rarely the case, however it provides a simplified base to study other parameters), then the sag is the height difference between the conductor's lowest point and the height of the supporting points [3].During the design (and construction) phase many parameters are to be considered.Among them, the calculated tension, the safety distances (clearances), the location of rural areas etc.Thus, mechanical modeling as well as geospatial data are usually employed [4].The design stage results to certain routing, placement of towers, tower types, conductor sag and tension throughout the route [5].Different types of conductors are used for the transmission of electrical energy e.g.AAC (All Aluminum Conductor), AAAC (All Aluminum Alloy Conductor), HTLS (High Temperature Low Sag), ACSS (Aluminum Conductor, Steel-Supported), ACSR (Aluminum Conductor-Steel Reinforced) with ACSR being probably the most usual choice for transmission lines.ACSR has a galvanized steel core that carries the mechanical load and outer strands made of high purity aluminum that carry the current [6].To meet changing necessities, ACSR is accessible in an extensive variety of steel substance -from 7% by weight for the 36/1 stranding to 40% for the 30/7 stranding.Early ACSR outlines, for example, 6/1, 30/7, 30/19, 54/19 and 54/7 stranding, included high steel content, 26% to 40%, with accentuation on quality because of the fear of vibration fatigue.Today, for bigger sizes, the most utilized standings are 18/1, 45/7, 72/7, and 84/19, involving a scope of steel substance from 11% to 18%.For the modestly higher quality 54/19, 54/7, and 26/7 standings the steel substance is 26%, 26% and 31%, respectively.The high-quality ACSR 8/1, 12/7 and 16/19 standings are commonly utilized in special cases (e.g.intersections) [6].Overhead transmission lines are subjected to a variety of environmental stresses during their lifetime.Sag or dip is considered in order to keep tension as low as possible.Sag is conversely corresponding to the transmission line tension [6].As the ground level varies in hilly areas so, the sag also does not remain constant [7].Wind is a main common factor to most transmission lines and thus wind impact is often investigated (e.g.[6]).The minimum distance of a conductor from the ground is set by each county (and usually it also depends on the installations found-or to be constructed-under the line) but some usual distances are shown in Table I.

II. MECHANICAL DESIGN OF A TRANSMISSION LINE
The sag of a transmission line depends on the following factors: the conductor's weight, the span (distance between the

D. Case 4
In Case 4, temperature is set to 50 o C but the wind speed is set to 50 N/m 2 .The conductor tension increases while sag is hardly affected (Table V).

V. CONCLUSION
A significant factor in overhead transmission line design is sag and tension calculation which is performed considering the potential environmental stresses that the transmission line is expected to suffer throughout its life time.The most common environmental stress factors are wind and temperature.Their impact is investigated in this paper, considering a part of an actual transmission line in Pakistan modeled in ETAP.Four different cases are considered and results show that an increase in temperature has a direct impact on sag whereas an increase in wind has a direct impact on tension. Abbasi

TABLE I .
VOLTAGE WITH GROUND CLEARANCE LEVEL