TRANSMISSION ISSUES AND POWER EXCHANGES IN TEXAS

Transcription

1 ABSTRACT TRANSMISSION ISSUES AND POWER EXCHANGES IN TEXAS Harold L. Hughes, Jr., P.E. Manager of Engineering Section Public Utility Commission of Texas Austin, Texas Tile electric transmission system in Texas has (,'\'(i1vl'u over the years to its present state, in order to "I\!VIJ' reliable service and reduce the amount of le"(,'1 \'t' capacity any individual utility needs to 1J1,IIIlI:lin. Presently there is pressure on the 1I,II.,lllission owning utilities by several parties, III itllli '! distribution cooperatives, cogenerators, and 1:1I1!l.' injustrial customers, to grant wider access to lill.',)''>icm. This pressure is coming at a time when 11,llhllllssion lines are becoming increasingly difficult to hulld. This paper presents a historical background \Ill lin: development of the transmission system and I.k"l'rJllCS the problems of assessing the impact and pll'i',',ly pricing certain bulk power transactions, In :Il d II ill, it briefly describes the Electro-Magnetic I Il'ld" problem and how it relates to new transmission IillL,,'nstruction. 1>1';\ I J.,OPMENT OF TRANSMISSION SYSTEM III understand current transmission issues in Il',IS and the operation of the bulk power system, a lillk h,lckground on the development of the state's 11:1I1Silll,,>sion system may be helpful to put these... Ill" 10 perspective. Early electric utilities in Texas \ 'lii1d hest be described as plants, set up in individual 1\1\\'11' throughout the state, intended to serve only the illlj1i\'dl:lte community. These plants, built to provide rull'lv local lighting service, were unreliable and inl'lfllll'nt. There was practically no demand for Pll\\ l'l ror industrial purposes. There were very few 11\1~' I L( Inncctions with other communities or systems.,1,1 I.y tems had a single distribution circuit. If 1Illll1iL occurred, the entire town would be without PlI\\' until repairs had been made. The operations II l't"': l'ldom profitable, and raising money for power planls was extremely difficult. Because of these problems and the limited market for electric power, these small companies were not able to take advantage of the improvements in improved technology for generating facilities, The utilities began solving the service problems caused by individual single circuit plants by interconnecting with other utilities. In Texas, these interconnections started in 1913 when Texas Power and Light Company completed the first high-voltage transmission line in the state. It was a 60,000 volt line connecting the Fort Worth Power and Light Company plant in Fort Worth with the Texas Power and Light plant in Waco, by way of Cleburne and Hillsboro. After America's entry into World War I, the pressures of the wartime economy created an even greater need for the electric utility companies in Texas to expand and interconnect. Texas Power and Light Company built 450 miles of new transmission lines and at the end of 1918 was serving 91 communities. Houston Lighting & Power was also extending service to neighboring towns and establishing interconnections with neighboring utilities, All told, HL&P expanded into nearly 70 communities during the 1920s. In West Texas and South Texas, lines were also being built and interconnections made. Since service territories were not strictly defined, competition for loads sometimes led utilities to race each other to build lines, not letting even "niceties" such as rights-of-way block progress. During the 1920s, improvements in high-voltage line construction were introd uced, such as the now familiar creosoted pine H-frame structures. These new transmission lines let the utilities extend service to more communities while providing a way to interconnect their systems and to exchange power. 51

2 Selling power between utilities, rather than building additional plants, meant lower rates. With America's entry into World War II, the utilities were once again stimulated to increase transmission line construction. Although it was a shock to the population at large, the electric utilities in Texas had anticipated America's entry into the war and were well prepared for wartime demands. As early as 1941, defense planners had conceived a "power pool" arrangement that would tie investor-owned utilities in Texas to the dams along the Lower Colorado, Brazos, and Guadalupe rivers. In the spring of 1942, operating arrangements were set up among Houston Lighting & Power, Public Service Company of San Antonio, the City of Austin, Lower Colorado River Authority, and Central Power and Light. The organization, known as the South Texas Interconnected System, was the forerunner of what would later become the Electric Reliability Council of Texas (ERCOT). After World War II, pent-up consumer demand resulted in a tremendous growth in electric demand. Meeting the exploding demand required more generating capacity and more transmission lines. The increasing size and output of the new plants required larger transformers and higher voltage lines. This expansion was so great that by 1953, Central and Southwest Companies were spending more money for line building than for new generation. For the electric utilities, probably the most important event of the 1960s was the famous New York blackout. On November 9, 1965, a massive power outage in the Northeast plunged 33 million people into darkness. The integrity of the nation's electric power system, which had seemed almost invincible, was dramatically called into question. President Lyndon Johnson asked the Federal Power Commission to investigate. In 1967, the Commission determined that a continuous supply of electricity had become so vital to the nation's economy and security that the electric utility industry should take steps to increase the overall reliability and lessen the chances of such a blackout ever occurring again. In response to the blackout, and in order to head off federal intervention, the industry formed reliability councils to jointly plan and interconnect their systems. In Texas, the Electric Reliability Council of Texas 52 (ERCOT) was formed to coordinate operations. With the formation of ERCOT, rules and procedures were formalized for the operation of the bulk power system and the framework was set for the current power exchanges. There are two primary types of power exchanges; direct sales and purchases between adjacent utilities, and exchanges that involve more than two parties, known as wheeling. Both types of these transactions will be described below. POWER SALES AND PURCHASES When two utilities are directly interconnected, sales of electricity occur when the selling utility increases its generation by the exact amount the buying utility decreases. Perhaps the easiest way to explain this is with an example. Utility A wants to sell 100 MW to directly interconnected Utility B for a certain time period. The first step in the transaction is for the utilities to agree on an exact start and stop time for the transaction. For example, let us suppose that the transaction will begin at exactly 1:00 p.m. and end at 11:00 p.m. At the start of the transaction Utility A will increase its generation by 100 MW and Utility B will simultaneously decrease its generation by 100 MW. The 100 MW will then flow from Utility A to Utility B via the transmission system. Since electricity follows all paths from the source to the destination based on the laws of physics, there is no control of the exact path the electricity will follow from Utility A to Utility B, as shown on Figure 1. WHEELING Now suppose that Utility A wants to sell to Utility C with which it is not directly interconnected. In order to consummate the transaction the transmission facilities of utility B will have to be used. This transaction where the facilities of a third party, that is neither the buyer or the seller are used is called wheeling. In an interconnected system, however, not only the transmission facilities of the buying, selling, and wheeling utility are involved but also all utilities in the system that are even indirectly interconnected are impacted by the transaction. As shown by Figure 2, the actual path the electricity will follow is the path of least resistance. This flow of electricity over the lines of other utilities that are not directly involved in the wheeling transaction is referred to as the loop flow or parallel path problem.

3 FIGURE 1 --If-- Interconnections Power Flow FIGURE 2 --If-- Interconnections Power Flow 53

4 The problems the loop flows cause are twofold; first, there is the difficulty of measuring the impact of the transaction and, second, the problem of devising a tariff that fairly compensates all the parties for the transaction. Most wheeling tariffs in the United States simply ignore the parallel path problem with payments usually limited to a "postage stamp" method where a set charge is billed to the wheeling utility by utilities that are in a direct "contract path" of the transaction. The current wheeling tariffs in Texas do attempt to measure the loop flows and compensate those utilities who are not on the contract path. The tool used as the basis for payment is a load flow study. LOAD FLOW STUDIES In order to safely and efficiently operate a power system, the system voltage levels and the loading of lines and equipment have to be known in advance for all points in the system under different conditions. Hand calculations would be almost impossible since the solution to complex network flows involve the solution of numerous simultaneous equations. Load flow studies are simply computer simulations of the flows on all points on a network under specified conditions. If only one wheeling transaction is taking place then taking the difference between the before and after transaction load flows would be a straightforward method of assessing the impact of the transaction. On most utility systems there is rarely only one transaction taking place; when multiple transactions are taking place simultaneously it becomes very difficult to assess the proper impact of each of the individual transactions. If we start with a base case load flow which includes only native load with no wheeling transactions and change load flows with each transaction included, we encounter two problems. First, it may not be possible to create such a base case without load reduction and/or fictitious generators, since some utilities will require the transfers to serve their peak load. Second, ignoring all but a single transaction in such analysis misrepresents reality, since it is almost certain that more than one transaction will be occurring during some periods. Alternately, if we begin with a procedure that starts with a no-transaction base case and add transactions in the order of contract dates, then the results for each transaction will depend upon its place in the order, so one user could in effect be rewarded for early contracting. This could also result in situations where a single buyer could have two transactions with a seller with different charges due solely to different contract dates. Cancelling a transaction low in order would necessitate reevaluation of all higher-order transactions. Finally, if we attempt a decremental approach, where we start with a base case that includes all wheeling transactions and then compare it to change cases where each wheeling transaction is removed one at a time, we still encounter problems. The main problem with this procedure is that the transactions included in both the base and change case will probably not actually occur simultaneously during all periods, so their presence can misrepresent reality and significantly distort the results. As shown above, regardless of the method used to select the base and transaction cases, we can encounter problems. This is why it is practically impossible to define an objective procedure for evaluating transactions. Care and subjective good judgment must be used when these evaluations are made. PAYMENT Even if the correct tool for calculating the load flows is selected, there is still another problem; how to calculate the results. After load flow studies are run, on a before and after basis, the results are usually tabulated in a table similar to Table I. Column 8 summarizes the; net change in loadings on the utility's lines caused by the wheeling transaction. The difference in the methods depends upon how this column is added. Some argue (principally cogenerators who will always be wheeling users but not providers) that negative changes should be subtracted from positive changes. In this case the party desiring the wheeling would receive a credit for unloading a utility's lines and freeing up capacity just as it receives debits for increasing line loads and reducing available transmission capacity. This results in a low impact, as shown in column 8. Many 54

5 TABLE 1 MW MILE METHOD EXAMPLE [1] [2] [3) [4) [5] [6] [7] [8] LINE BASE BASE WHEELING POSITIVE NEGATIVE ABSOLUTE NET I.D. MILES MW-MILE MW-MILE CHANGE CHANGE CHANGE CHANGE A , (46) 46 (46) B 1, ,842 51, (220) 220 (220) C ,012 42,790 3, , TOTAL 2, ,525 97,037 3,778 (266) 4,044 3,512 utilities argue that the absolute value of each change should be added up to compute the impact. They argue that decreased loading on a given line only effects the calculation for line losses and is otherwise only negligibly beneficial since lines are not normally loaded close to their maximum. Accordingly, they feel they should be compensated for use of the unloaded line since change in line loadings indicate that the transaction impacts the line. This resu Its in a higher impact, as shown in column 7. These arguments can perhaps best be explained by using an analogy using pipes and water rather than electricity. Suppose we have a water utility company that is made up of one pump and three pipelines serving two customers, as shown on Figure 3. Company B is also interconnected to companies A and C for back-up. If company C wants to transfer or sell water to company A, then they must use the facilities of Company B to complete the transaction. When the transaction takes place the flows appear as shown in Figure 4. The paradox or problem can now be clearly seen. Company B has benefitted from the transaction between A and C because flow on two pipes has ceased and on the third shorter pipe has increased only 50 gallons per minute (GPM). However, the transaction clearly could not have taken place without the presence of Company B, so, how should company B be paid? If we use the net changes as the basis for payment, then company B would be paying the other companies for the transaction. However if we use the absolute value of the changes, then the result is a charge almost as large as the native load and consequently higher charges. The choice is not a clear cut economic one but rather an ethical one of what is fair to all the parties involved. TRANSMISSION LINE CONSTRUCTION AND EMF Almost every time a new transmission line is proposed, there is the strong likelihood that people living adjacent to the proposed line will intervene to stop its construction because of fears that the electromagnetic fields (EMF) from the line could be harmful to their health. Unfortunately, the evidence on the health effects of EMF is inconclusive and typically what happens in the cou rt rooms or hearing rooms is that attorneys for the opposing parties put on the stand scientists with different viewpoints on the stand. Typically, the attorney for the intervenors will ask the scientist or expert for the utility if he can categorically say there is no risk associated with EMF. A responsible scientist could never make such an unequivocal statement since there is always the possibility that something previously not dreamed of could be discovered. Therefore, no reasonable amount of research would ever allow a determination of zero risk. With the admission that there could be some risk, the controversy continues with the lawyers on both sides badgering the experts into taking increasingly harder stands on their positions than they 55

6 FIGURE - 3 BASE CASE - Company B NATIVE LOAD ONLY Tie 10 COIfIPOIlY II. Requires 100 GPM llrl::==:ft== Tie 10 Company C FIGURE GPM Transfer from Company C 10 Company A Tie to Company A Requires 100 GPM 56

7 ever would in a non-adversarial proceeding. The judge or Commissioner is then left with the very difficult job of trying to properly decide the true impact of a proposed line on the health of the community. CONCLUSION Given the problems with increased utilization of the transmission system and the risks inherent in any radical change to the existing system, the challenge for the utilities, cogenerators, and regulators alike will be to: 1. Determine the real impact of wheeling transactions; 2. Devise rates that promote "good wheeling" which brings power produced at low cost to an area that has only higher cost generating alternatives, and discourage "bad wheeling" which benefits only one party and does not contribute to the overall efficiency of the system; 3. Deal with the EMF problem and build needed lines; 4. Do all of the above without jeopardizing reliability. 57