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Introduction
In a competitive power supply business environment, line ampacity
predictions are required by electric power utilities for economic
generation planning, contingency planning, security analysis, and
for normal and emergency operation of electric power systems. The
line ampacity system featured in this article calculates ampacity
from general purpose National Weather Service (NWS) forecasts and
does not require additional hardware on power lines. By designing
the ampacity expert system with objects and rules, it can be easily
implemented in small and large electric companies.
The Line Ampacity System is a PC/Windows-based, power-line ampacity,
expert system program for the estimation of line ampacity during
steady state, dynamic state and transient conditions. It was
developed by the application of artificial intelligence using
object-oriented knowledge base design of the power line environment.
The expert system provides hourly values of line ampacity up to
seven days in advance and is used for the operation, planning, and
design of transmission and distribution lines at all voltages. The
program is an economical line ampacity system that does not require
the installation of additional transmission line hardware, conductor
temperature sensors, meteorological sensors or telecommunication
system, and is easily implemented in all geographic regions.
Line Rating Methods
Electric power companies generally assume constant power line
capacity by assuming conservatively the values of ambient
temperature, wind speed and solar radiation required in the
calculation of ampacity. Most common assumptions are that ambient
temperature is 40 degrees Celsius, wind speed is 2 feet per second,
there is a clear sky, and the maximum conductor temperature is 80
degrees Celsius. During favorable weather conditions when ambient
temperature is lower than the assumed maximum or when wind speed is
higher than the assumed minimum or during cloudy conditions, higher
line ratings are possible without exceeding the maximum temperature
of the conductor. For these reasons, many utilities have started
adapting line ratings to actual weather conditions. Dynamic line
rating systems are also proposed that take into account the heat
capacity of conductors. Existing real-time line ampacity systems
require continuous input of data from line temperature sensors,
meteorological sensors and/or on-line connection to a weather bureau
and line current. Sometimes elaborate telecommunication systems are
also necessary to bring data from remote locations to a host
computer where line ampacity is evaluated.
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