01-08-2016, 03:01 PM
Sag-Tension Calculations:
Refinements and Enhancements Made by Trimble Energy Solutions
Abstract
SAG has traditionally count stress programs flexibility stress characteristics of conductor
ALCOA graphic method. This equation is used to refine and enhance the input by
Other definable variables and these results with the selection standards, Trimble has created a more
Design and operation of transmission lines for comprehensive tool. Discussion of this paper
Modifications and enhancements related to the input data, and explains how these changes
Transmission lines plan to improve capabilities. Calculation methods are also provided.
Introduction
The ALCOA graphic method traditionally has been used to calculate sag-tension. Using this
methodology, conventional programs calculate the conductor’s sag-tension characteristics
without reference to the characteristic’s influence on other components of a transmission line.
Trimble has refined the stress-strain coefficients used as input by the ALCOA method. In
addition to this sag-tension data, the program inputs consider conductor composition, stressstrain properties, adjustment for temperature and creep, the annealing factor, and tolerances.
These factors enable the program to calculate regular sags and tensions of ruling spans, in
addition to providing users with access to new output on structural loads, actual spans, inclined
spans, regularly occurring loads, rarely occurring loads, low point and sighted sags, and uplift
tensions.
0 Input Refinements
To predict the performance of installed conductors, the Trimble program requires two types of
input: conductor parameters and conductor variables. Conductor parameters are properties
affiliated with a particular conductor type. Conductor variables refer to external factors that act
with the conductor’s parameters and influence the performance of the conductor in field
application.
Conductor Parameters
The Trimble system provides a user-selectable window of commonly-used conductors, including
conductors made of two components (e.g. ACSR), homogeneous conductors (e.g. AAC), and
fictitious two-component conductors made from a material “equivalent” to a single component
conductor. Unlike traditional sag-tension programs that rely on a database to define properties for
the selected conductor, these values are calculated by an auxiliary program. Developed by
Trimble, this program works with the sag-tension program. The calculated properties associated
with the selected conductor are used in analysis calculations and include:
• Stress distribution between the outer and inner components (useful to evaluate Aeolian
vibration performance)
• Conductor tension at higher temperatures, which is carried entirely by the inner
component resulting in smaller sags. This feature can be turned on or off at the discretion
of the user.
As new conductors are requied, the auxiliary program requires minimal input: conductor type,
stranding, and size (e.g. ACSR, 26/7, and MCM). Using this data, the program calculates the
required properties. These calculated values can be reviewed, modified, and stored for use by the
sag-tension program. Coefficients for new conductors are also calculated using known
coefficients originating from third parties, such as The Aluminum Association and ALCOA, and
standard or conventional stress-strain-creep (S-S-C) charts. This feature makes it faster and
simpler to analyze new conductors.
Stress-Strain Properties
Traditionally, stress-strain (S-S) properties used in the ALCOA method have been
defined through polynomials of the third and four orders, namely four or five coefficients
for each component. While these polynomials are accurate and satisfactory, they result in
errors at higher conductor strains.
Refinements and Enhancements Made by Trimble Energy Solutions
Abstract
SAG has traditionally count stress programs flexibility stress characteristics of conductor
ALCOA graphic method. This equation is used to refine and enhance the input by
Other definable variables and these results with the selection standards, Trimble has created a more
Design and operation of transmission lines for comprehensive tool. Discussion of this paper
Modifications and enhancements related to the input data, and explains how these changes
Transmission lines plan to improve capabilities. Calculation methods are also provided.
Introduction
The ALCOA graphic method traditionally has been used to calculate sag-tension. Using this
methodology, conventional programs calculate the conductor’s sag-tension characteristics
without reference to the characteristic’s influence on other components of a transmission line.
Trimble has refined the stress-strain coefficients used as input by the ALCOA method. In
addition to this sag-tension data, the program inputs consider conductor composition, stressstrain properties, adjustment for temperature and creep, the annealing factor, and tolerances.
These factors enable the program to calculate regular sags and tensions of ruling spans, in
addition to providing users with access to new output on structural loads, actual spans, inclined
spans, regularly occurring loads, rarely occurring loads, low point and sighted sags, and uplift
tensions.
0 Input Refinements
To predict the performance of installed conductors, the Trimble program requires two types of
input: conductor parameters and conductor variables. Conductor parameters are properties
affiliated with a particular conductor type. Conductor variables refer to external factors that act
with the conductor’s parameters and influence the performance of the conductor in field
application.
Conductor Parameters
The Trimble system provides a user-selectable window of commonly-used conductors, including
conductors made of two components (e.g. ACSR), homogeneous conductors (e.g. AAC), and
fictitious two-component conductors made from a material “equivalent” to a single component
conductor. Unlike traditional sag-tension programs that rely on a database to define properties for
the selected conductor, these values are calculated by an auxiliary program. Developed by
Trimble, this program works with the sag-tension program. The calculated properties associated
with the selected conductor are used in analysis calculations and include:
• Stress distribution between the outer and inner components (useful to evaluate Aeolian
vibration performance)
• Conductor tension at higher temperatures, which is carried entirely by the inner
component resulting in smaller sags. This feature can be turned on or off at the discretion
of the user.
As new conductors are requied, the auxiliary program requires minimal input: conductor type,
stranding, and size (e.g. ACSR, 26/7, and MCM). Using this data, the program calculates the
required properties. These calculated values can be reviewed, modified, and stored for use by the
sag-tension program. Coefficients for new conductors are also calculated using known
coefficients originating from third parties, such as The Aluminum Association and ALCOA, and
standard or conventional stress-strain-creep (S-S-C) charts. This feature makes it faster and
simpler to analyze new conductors.
Stress-Strain Properties
Traditionally, stress-strain (S-S) properties used in the ALCOA method have been
defined through polynomials of the third and four orders, namely four or five coefficients
for each component. While these polynomials are accurate and satisfactory, they result in
errors at higher conductor strains.
