PTDF and TLR from a power marketer´s perspective

Power system operators maintain transmission system reliability by controlling potential transmission overloads. As regional power transactions increased markedly over the past few years due to open access of the bulk power transmission system, Transmission Loading Relief (TLR) procedures have been developed by the North America Electric Reliability Council (NERC) to provide a mechanism for control areas to curtail transactions that are deemed to cause transmission overloads. The current TLR procedures rely on a set of Power Transfer Distribution Factors (PTDFs) to evaluate the impact of each transaction on the transmission overload. However, PTDFs provide only approximate and sometimes even inaccurate results, and are not suitable for the next day line loading forecast. As a power marketer, Power Team is concerned with the accuracy of the PTDF approach. This paper discusses some of the PTDF deficiencies and proposes a method to improve the accuracy and use of the PTDF approach for transmission overload control