|Title:||Reactive power and security studies in an open power market|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Reactive power (Electrical engineering)
|Department:||Department of Electrical Engineering|
|Pages:||xix, 161 leaves : ill. ; 31 cm|
|Abstract:||The traditional regulated and monopoly structure of power supply industry throughout the world is eroding into an open-access and competitive environment. Integrated generation, transmission and distribution functions in the power supply chain are unbundled. Responsibility of maintaining reliability and security has been transferred to an organization generally referred as independent system operator, which is independent of different businesses entities. Delay of transmission facility construction, unpredictable pattern of load increase and economic incentives have made system operation conditions more stressed than ever before. Various stability problems have been recognized as the main threats to secure system operation. Security, especially transient security, constrained system operation is a difficult task facing a system operator in the electricity market environment. It is the first major topic discussed in the thesis. A systematic approach for transient security enhancement with single and multiple contingencies under the electricity market environment is developed. The proposed corrected hybrid method is an effective transient stability assessment method. The stability index called the corrected transient energy margin given by the method bears a linear relationship, within a useable range, with important control variables such as generation exchanges. An optimal rescheduling scheme taking generator bids into account to enhance transient security for single potential unstable contingency is proposed. The methodology also responds to price signals since it is important in the deregulated environment. Difficulties arise when several unstable contingency have to be enhanced. Different candidate contingencies may motivate different rescheduling strategies because the critical generator group is different in each case, or the sensitivity of the stability margin to power exchanges between generators is different. A global index, which reflects the global transient security enhancement and deals with trade-off between contingencies, is proposed in the thesis. Using this index and generator bid information, a transient security enhancement approach for multi-contingencies is also developed.|
The second major topic investigated in the thesis is reactive power management in the electricity market environment. Reactive power support services are crucial for secure operation of electric power systems. To improve competition and efficiency of provision of reactive power support and voltage control services, procurement and charge of reactive power support and voltage control services should be unbundled from electricity service and transmission service. Costs of different suppliers should be precisely identified and properly compensated for and different users should only be charged exactly that part of the requirement caused by them. Different from active power, the objective of reactive power support procurement is not unique. In different power systems, the objectives could be different and are dependent on the structures and operating characteristics of the systems concerned. Subsequently, methods used to allocate reactive power support costs to consumers are different. Three approaches have been developed in this thesis to solve the problem of procurement and charge of reactive power services. Regarding cost allocation, one approach considers that some reactive power support costs should be the responsibility of generators while the other two assume all should be allocated to the loads. The latter two approaches use the Aumann-Shapley cost allocation method to make the allocation process more economically efficient and equitable. Reactive power optimization taking voltage instability into account is also investigated in the thesis. Increased loading and exploitation of power transmission networks appear to have created a special voltage security problem, namely voltage stability. Traditional voltage profile criteria are not sufficient for electric power systems concerning the voltage stability problem. A reactive optimal power flow formulation is proposed to minimize reactive power support costs while respecting the voltage stability margin requirement.
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