Comprehensive dynamic security assessment of Bangladesh power system

Abstract

Power system security analysis is a key to reliable operation at maximum efficiency. Security analysis in this context refers to the ability of a power system to withstand pre-specified disturbances called contingencies. A power system must be able to survive dynamic events, and hence dynamic security assessment is more computationally intensive as it requires the electro-mechanical transient stability analysis of the system which concerns the transient behavior of the power system when moving from the pre- to post- contingency operating point. Dynamic security assessment is an evaluation of the ability of a certain power system to withstand a defined set of contingencies and to survive the transition to an acceptable steady-state condition. This is dependent on the transient stability evaluation which provides information in relation to the ability of a power system to retain stable operation during major disturbances resulting from either the loss of generation or transmission facilities, sudden or sustained load changes, or momentary faults. In the event of disturbances, the electro-mechanical oscillation of synchronous generator will be used to measure the transient stability. It is determined by observing the variation of the rotor angle as a function of time throughout the duration of the fault. The transient stability depends on the magnitude of the fault, duration of the fault and the speed of the protective devices. If the system is transiently stable, the oscillation of the rotor angle will damp down to a safe operating limit. Dynamic security assessment identifies those disturbances that cause instability and the results of the transient stability analysis are used to determine the system’s security level. This thesis demonstrates a methodical approach to dynamic security assessment. The method is based on a combination of voltage and angular criterion, N-1 and N-2 contingency analysis, transient voltage dip, transient stability analysis, and use of a performance index. A combined contingency ranking based on bus phase voltage and phase angle, and stability margin for all machines in a power system is used. The method is very effective for secured planning and operation of a power system, and for protection scheme design. The method is applied to the Bangladesh power system network (BPSN) for dynamic security assessment of the system. Critical buses and the paths connecting them are identified. These forms the backbone of BPSN and the system is most vulnerable at these locations as any serious contingency involving these nodes may lead the system to partial or complete blackout. Additional protective measures should be taken for the most critical buses of the system to prevent sudden system collapse or blackout.