Since 1998, when deregulation really started transforming the power industry, the volume of energy transactions across the power grid has increased significantly, placing a strain on transmission systems.

Although utilities commonly make deals to buy and sell electricity with other utilities or supply power needs to large industrial customers, the practice has increased fourfold over the last few years, estimated Stephen Lee, area manager of grid operations at the Electric Power Research Institute, an industry group based in Palo Alto, Calif. Further complicating matters, the various services of utilities—power plants and distribution and transmission lines—have become unbundled to varying degrees in different states as
deregulation is taking effect. Not only are transactions becoming more numerous, but they are involving longer distances.

To cope with these changes, EPRI and the North American Electric Reliability Council, or NERC, an industry group that sets reliability standards for interconnected electric transmission system operations, developed the Interchange Distribution Calculator, an online data processing and communications service to help manage the flow of electricity.

IDC has been operational since October 1999 in the Eastern Interconnection,which includes the eastern portion of the United States and Canada. Lee, who is the EPRI project manager of the NERC IDC Operation Services, believes that the IDC can ensure an orderly and equitable process for eliminating transmission overloads.

Regional transmission organizations, also known as RTOs, are being formed in the United States. They will oversee power transmission in a defined geographic area and ensure open access to the transmission grid. Within these areas, the activity of buying and selling power is a sort of balancing act between security coordinators, who keep an eye on transmission line activity, and marketers, who buy and sell electricity generated by independent power producers. Marketers are not privy to information accessed by security coordinators, and the job functions of each are kept separate.

Energy transactions are normally conducted through what is known as a contract path, which designates points of delivery and receipt as well as intermediate
points. However, these transactions may cause congestion on transmission lines of other utilities because electricity flows in parallel paths and not in contract paths. Security coordinators act as gatekeepers, monitoring transmission lines, identifying transactions that are causing congestion, and taking steps to relieve congestion according to NERC rules.

In the Eastern Interconnection, one of the tools that the security coordinators use is IDC. The IDC system, which was jointly developed by Open Access Technologies International of Minneapolis and Perot Systems of Dallas, is basically an Internet Web server, operated by a cluster of computer workstations. It examines more than 1,000 interchange transactions at any one time with respect to their impact on 700-plus transmission facilities.

The IDC engine also considers factors of topology of power lines, transformers, and generators when computing a list of transactions to be curtailed in priority order, if necessary, to eliminate overloading. It uses the NERC electronic transaction tagging system, or E-tag, to track interchange transactions and supports NERC policy on transmission curtailment procedures. These data are continuously submitted to the IDC computer workstations. The IDC system also provides a computer model of the entire Eastern Interconnection and calculates the effects of transactions on the power grid.

Transactions are prioritized according to rules set by NERC. Once the IDC system determines curtailment priorities, security coordinators in the affected control areas implement any necessary curtailments, and handle system reloading when the congestion diminishes. Marketers who are affected would have to find other means of fulfilling their contractual obligations, perhaps by arranging to send the power differential from another source.

In a new development, marketers will be able to evaluate the current congestion status of various bottleneck areas and avoid curtailment.