Using Real-Time Ground Clearance Measurements to Control Line Thermal Rating

SWING VBA and CATCH VBA

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Developed by Kinectrics and used for over a decade by a major North American utility to address errors in traditional Ruling-Span methods

Validated by the IEEE Task Force on Bare Conductor Sag for combined short and long spans.

Uses the most advanced description of conductor stress-strain characteristics from the STESS conductor library

Integrated with the IEEE 738 ampacity model in CATCH VBA modules

Extended to calculate conductor temperature, wind speed, steady state or limited-time ratings using measured clearance in any one span along with, line current and ambient temperature

Maximize thermal ratings and comply with regulations

SWING VBA is an easy-to-use computer program designed by Kinectrics Inc. to assist utility and ISO staff in the modeling of transmission line high-temperature sags and ground clearances. SWING VBA is based on extensive research, testing and two decades of practical experience in high-temperature operation of ACSR conductors up to 150° C. This highly effective tool offers proven value in helping utilities and other industries meet NESC, CSA or other regulations for minimum ground clearance.

Multiple cost-effective benefits

SWING VBA and its supervisory modules in CATCH VBA provide multiple cost-effective benefits  for transmission line designers and operators, including:

• Accepting line feature data (span lengths, attachment heights above ground features) in an Excel spreadsheet format, minimizing costly data entry errors
• Predicting conductor clearance, sag and tension in all spans as a function of conductor temperature
• Accepting a measured clearance (anywhere along a span), sag, or tension value from real-time monitoring systems to predict the conductor temperature
• Using measured clearance, line current, and ambient temperature as inputs to estimate the effective crosswind speed along an entire stringing section

State-of-the-art field verified program

SWING VBA  calculates the sags, tensions and clearances in every span of a stringing section between dead-end anchor towers. As conductors heat up and cool down, the horizontal tension is normally assumed to be equal in every span. A small part of this tension is transferred along the insulators as they swing off vertical. This small component makes a   large difference in the estimated sag-temperature relationship and is ignored in traditional sag-tension calculations.

At each insulator, the tension balance is nearly equal, making the problem numerically challenging. SWING VBA uses advanced numerical techniques to ensure rapid and stable convergence, even in an application with 282 spans in a single stringing section. With conductor profiles from helicopter or ground-based LIDAR surveys, SWING VBA can be used to determine the temperature at which insulators now hang vertical–an important benchmark for the loadingand creep history of the conductor.

Key features

SWING VBA  considers the insulator length, span lengths, vertical and horizontal distances to underbuilt features or monitoring points, birdcaging temperature, limiting compressive stress in aluminum layers and sixth-order polynomial description of stress-strain relations for each conductor in the provided library. From a supplied conductor temperature, SWING VBA accurately calculates the sags, tensions and conductor profiles in every span.

CATCH Clr_Temp is an Excel VBA-based module that accepts a measured conductorclearance and iterates the SWING VBA program to converge on the corresponding conductor temperature.

CATCH Clr_WSPD is an Excel VBA-based module that extends the conductor temperature calculation from the Clr_Temp module, along with input values for solar radiation, ambient temperature and load current. Clr_WSPD computes the effective wind speed, at right angles to the conductor, averaged over the entire stringing section. This wind speed minimizes uncertainties about wind direction and sheltering, allowing utilities to use their power lines aslong-axis hot-wire anemometers whenever there is sufficient line current to cause some temperature rise.

Supported Data Sources

CATCH VBA modules are normally used with the highly successful Siemens-Milltronics sonarclearance monitoringequipment, which is portable, quick to install with no live-line work and can cost less than a tenth of tension monitoring or machine vision equipment. Kinectrics has applied this technology successfully since 1987. We offer a comprehensive training package that includes a full set of the monitoring equipment and software.

For weather data, Kinectrics has supplied, commissioned and delivered training for the standard Campbell scientific meteorology equipment including communications equipment.

The CATCH VBA system is modular. It can be reconfigured at low cost to accept a real-time value of tension or sag to extend the accuracy and function of existing thermal rating equipment. CATCH can also be customized to provide limited-time ratings using the IEEE 738 ampacity model and the heat capacity of the selected conductor along with the calculated wind speed from the Clr_WSPD module

For more information, contact

William Chisholm, 416.207.6000 x6982, W.A.Chisholm@ieee.org

IBM or LINUX compatible PCs - Colour Monitor – Windows 95/98, NT, 2000 or XP - 2MB Hard Disk space, Microsoft Excel or Standard f2c / f77 FORTRAN complier