What is Sag and Tension in Transmission Lines and Formula Calculation

 

Sag and tension are two terms that describe the amount of weight per unit length of a conductor. The lower the sag, the higher the tension, and the higher the force. A CFBG-based sensor can measure both tension and sag. Read on for more information about CFBG-based sensors and how they calculate sag. Electrical Engineering is a field required a lot of knowledge.

CFBG-based sensor for power line strain calculates sag

In this paper, we present the results of a novel CFBG-based sensor for power line sag calculations. This sensor is insensitive to ambient temperature, electromagnetic field, or any other external parameter. The sensor itself consists of a clamp and special steel plate, which is attached to the CFBG. We demonstrate that the proposed system is capable of being embedded on a power line wire.

In addition to measuring sag, the CFBG-based sensor also measures flux density, which increases with transmission line sag. This measurement allows the operator to calculate sag without a power outage. Moreover, the CFBG-based sensor is easy to install and requires no special training. It can be used in existing power systems and is relatively cheap.

Variations in length of measured section affect CFBGFWHM spectral width

The spectral width of CFBG is dependent on temperature and elongation of the section being measured. This effect is linearly proportional to the thermal expansion coefficient of the OTL wire and the testing plate. Variations in elongation are attributed to differences in electric current flow and conductor temperature. The total length of the wire L affects the power line sag D. A lot you wondering about what is sag. This change in elongation has a major impact on CFBGFWHM spectral width.

To measure CFBG spectral width, a short segment of a power line wire was used. Then, a steel plate was glued to the wire. The entire system was placed in a climate-control chamber. The temperature range was set at 10 to 90 degC. In Figure 7a, the spectral characteristics of the CFBG reflected signal were studied. The results of the experiment revealed that, as the temperature increases, the entire spectral width shifts to longer wavelengths. This is the underlying nonlinearity of the strain applied to the transducer.

Effect of wind and ice loading on sag calculation

The Sag formulae used in Overhead Transmission Lines are valid for conditions with normal temperatures and no wind. However, the weight of a conductor covered with ice and subject to wind pressure is far greater than the weight of the conductor itself. Because ice acts vertically downward, the weight of the conductor and wind forces are often multiplied, making the total force acting on the conductor greater than the weight alone.

Generally, sag calculations are made for temperatures above normal and assume normal temperatures. In cold climates, wind pressure will change the sag length, which may result in an unexpectedly long or short sag. Another factor that should be considered is the weight of ice on the conductor, which will increase the net diameter and weight of the line.

Hollow conductors

In a transmission line, hollow conductors are used to minimize corona loss, and are a popular alternative to solid ones. These hollow conductors can be manufactured with a range of diameters for different transmission power and voltage grades. The formula calculation also takes into account the economic current density, which is relevant for the number of bundled conductors required. The bundled conductors can carry more current than single-stranded ones, but are not as flexible as hollow conductors.

When determining the optimal positions for conducting elements, you must first define the structure of the system. The NGroundBundle and 1-by-NPhaseBundle vectors represent the positions of conductors on a transmission line. The default conductor outside diameters are 3.5500 cm and 1.2700 cm. However, if the conductors are made of a more flexible material, then the resistance is greater than that of a solid conductor.

Bundled conductors

One of the key benefits of bundled conductors is the reduction in surge impedance and higher disruptive voltage. However, these benefits are limited by their larger charging kva and increased circuit cost. These are two important considerations to keep in mind when considering bundled conductors. One circuit would carry a huge amount of power if it had multiple conductors. A two-conductor bundle would provide electrical characteristics equivalent to one single conductor of up to eight inches in diameter.

In addition to minimizing surge impedance, bundled conductors in transmission lines will also improve loading capability and reduce circuit cost. The optimal separation between two parallel bundles is a minimum value, which is inversely proportional to the voltage gradient. A larger separation balances the effects of reduced corona performance, slightly increased circuit cost, and decreased reactance. Moreover, the gradient on the surface of the conductor is not uniform and varies cosinusoidally.

 

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