Determination of real-time available transfer capability in deregulated power systems

Abstract

In the past, power industry in many countries is monopolized by government or state enterprises. These utilities typically own generation, transmission and distribution systems for the whole country or a wide geographical area. Under this structure, each system usually has more than one control centers and divisions taking care of necessary responsibilites for power industry such as load flow analysis, load forecasting, system planning, automatic generation control, unit commitment or security analysis. Obviously, this is not an efficient structure and may cause corordination problem. In contrast, under the pool structure, all resources in the system are combined in order to increase reserve margins and increase the robustness of the system. Under the deregulated structure, single control center operates the system based on the policy provided by the board of governance. It is accepted that size of the system under the new structure is much larger and more complicated due to the increasing number of transactions. This may lead to the congestion and voltage problems that must be carefully concerned. In addition, it is reasonable to conclude that transmission system under the new structure may carry more load than the past since utilities have more options to purchase power from other areas than produce it by themselves similarly to the customers. This outcome of the deregulation has created to issue that, under this situation, what is the maximum transmission capability to deliver power from one area to another area (Total Transfer Capability- TTC) and what is the available power can be transferred over transmission facilities relative to the current operation conditions. Obviously, Available Transfer Capability (ATC), the optimum value between security level and commercial viability, is a premier answer for this situation. Currently, ATC values between selected pairs of transactions are calculated and posted for participants in hourly, daily, weekly and annually basis. However, this dissertation will concentrate mainly on real-time ATC determination. The technical challenge of the real time ATC calculation is how to calculate ATC values for a large-scale power system when time constraint is a limited resource. A good solution should consider all of security requirements that ensure the security of the system. This dissertation proposes an algorithm that is reliable and fast enough to handle with these problems. Thermal limits, voltage limits and stability limits are considered in this algorithm in both normal and ท-1 contingency conditions according ATC framework defined by North American Reliability Council (NERC).