Today's Most Important Transmission Game is Making Systems Work Harder, specifically by better allocating flows among circuits and enabling those circuits to accommodate higher flows. That was the center of discussion at much of the International Council on Large Electric Systems' (CIGRÉ) 42nd Session, held in Paris the last week in August. I co-authored a paper for the conference, in collaboration with Dennis Woodford of Electranix (Winnipeg, Manitoba, Canada) and Dale Douglass of Power Delivery Consultants (Schenectady, New York, U.S.), that estimated the leverage inherent in several enhancement options (Fig. 1).
Dynamic ratings, a powerful recourse in their own right, extend (see the red bars) the gains through other recourses, but have operational limitations and risk loss of life to conductors and splices. Making structural modifications to accommodate greater sag, an expensive game, offers still greater gain. High-temperature, low-sag (HTLS) reconductoring can be even more expensive, but can double a line's rating, though with an increasingly important penalty in losses. Reconductoring with greater cross-section avoids that penalty and can extend ratings even further, but usually at a very high additional price in tower rebuild. Conversion to dc, the most expensive option of all, can double or triple a line's contribution to path flow.
All of the measures except the last assume that system measures are taken to allocate more flow to the modified circuit. HVDC conversion (Fig. 1, row 5) does not since dc flow is independently controlled.
All of these recourses serve the same objective of greater path capability and each represents investment. Given those observations, Pierre LaPlace, a famous mathematician from some 200 years ago, suggested that investment be deployed among options such that the incremental cost/benefit ratio is the same for each — not a foreign concept to those familiar with economic generation dispatch.
My qualitative assessment in Fig. 2 interprets the data of Fig. 1 through LaPlacean eyes. Dynamic rating, clearly the least expensive way to gain transfer capability, deserves (and gets) the most attention. But the smarter we get at that game, the more expensive incremental gains become. Incremental cost approaches infinity when weather forecasters are clairvoyant, all hardware temperatures are known, and both are distilled by infinitely smart software that optimizes operator actions. That and other asymptotes may not be so hard to identify.
How much gain in flow will utilities see: if dynamic ratings were infinitely smart; if structure modifications dismissed clearance limitations; if all circuits were magically transformed to HTLS conductors and loss economics ruled the game; if, at the system level, flexible ac transmission system devices became infinitely smart and agile, allowing flow allocation limited only by the need for thermal redundancy; if selected circuits were rendered exempt from Kirchoff's laws through dc conversion?
Maybe allocation of R&D funds among increased power-transfer options would benefit from first estimating the prize associated with the total success of each.
Lionel Barthold founded and served as CEO and chairman of Power Technologies Inc. from 1969 to 1998. He has served on and chaired numerous committees in CIGRÉ and is a past president of the IEEE Power Engineering Society. Barthold is a fellow of the IEEE, holder of its Power Life Award and a member of the National Academy of Engineering. firstname.lastname@example.org