By Kim Wirgau
The Energy Policy Act (EPACT) of 1992 laid the foundation for wholesale electricity deregulation and ordered FERC to facilitate the transition1,2. Since the deregulation of the power industry, the generation side of the industry has flourished. The recovery of costs to build, operate, and maintain a generation plant as well as obtaining a rate of return on the investment has been straightforward. However, the transmission side of the business has floundered. It has not been clear on how to recover costs to build new lines let alone make a rate of return on the investment. Therefore, new significant transmission lines have basically not been built over the past 15 years, with few exceptions of course. The transmission system was never designed to operate as it is does today with most of the design margin having been depleted3. Reliability of the power system has degraded through time that can be seen by brown-outs and black-outs that have occurred with the situation most likely getting worse.
Paul Hines of Carnegie Mellon University published data on the frequency of large blackouts in the United States which shows how blackout frequency has been increasing4 over the last 10 years (see figure).
With the need for improvements to the transmission system, it is important to evaluate how the power system operates under various conditions. The normal method of evaluation of a power system under normal and emergency conditions is by simulation using a power flow program. A study of the power system helps locate problem areas and helps evaluate the effect of various system corrections.
When studies of the network indicate a power transfer problem into a load area, three basic methods to increase transmission line transfer capability are possible:
Improvement of line rating calculations
Reconductor
Addition of a new circuit
Line ratings are normally simulated as a static value. The actual value changes depending on conductor characteristics, weather, amount of sunshine, and even the location of the line. Recently, a more precise calculation of the limits has been given in the IEEE Standard 738-20065. In addition to improvements in the calculations, a computer program is also given to assist the engineer in making the required computations.
When considering reconductoring or adding a new circuit, the potential use of “composite core conductors” should be considered6. One of the new conductors is the aluminum conductor composite core (ACCC). The ACCC conductor has the following advantages over the traditional ACSR conductors:
Provides twice the ampacity
Incorporates more aluminum for conductivity
Has similar weight, diameter, and tension
Eliminates sag
Can be operated at higher temperatures (up to 200°C)
Utilization can help meet emission initiatives
Eliminates steel core which reduces EMF
Eliminates galvanic core corrosion
In summary, in today’s operating environment it is important to study the power system in various operating conditions (normal and emergency) to identify transmission weaknesses. Once transmission weaknesses are found, they can be improved by refinement of line ratings (small problems) and/or new conductors using new materials (major problems). These improvements must be then verified through computer simulations and economic evaluations.
References:
Energy Policy Act of 1992, H.R.776, //thomas.loc.gov/cgibin/query/z?c102:H.R.776.ENR.
Energy Policy Act of 1992, http://en.wikipedia.org/wiki/Energy_Policy_Act_of_1992.
Casazza, J., “Electric Power Deregulation-A Bad Idea?”, IEEE-USA Today’s Engineer Online, May 2005.
Hines, P., “The Frequency of Large Blackouts in the United States”, Carnegie Mellon University, March 2006.
“IEEE Standard for Calculating the Current-Temperature of Bare Overhead Conductors”, IEEE Std 738-2006 (Revision of IEEE Std 738-1993).
Engelbrecht, E., Francis, M., “The Use of Composite Core Conductor for Re-Stringing the Existing 220kV Circuits”, Composite Technology Corporation, July 2005, http://www.electricitycommission.govt.nz/pdfs/submissions/





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