Protective system enhancement using optimization technique in power grid

Abstract

Nowadays, Phasor measurement units (PMU) may be used to enhance power grid protection due to their flexibility, security and dependability properties. The decision of the digital protective relay highly depends on the digital signal filtering computing the fundamental phasors of line voltages and currents. However, during a transient condition, line current and voltage may include unwanted components such as dc exponentially decaying associated with the harmonics and sub-harmonics especially in the smart grid. The used digital algorithms always need few cycles for obtaining the accurate fundamental phasors which are undesirable in the protection field. The first approach proposed in this research work for reliable phasor estimation algorithm is to remove disturbance signals using optimized digital filter (ODF) and DFT algorithm. The obtained phasor algorithm has the required characteristics to remove the dc component and dump the sub-harmonic as well as harmonic components. The performance of the developed digital relay is tested using estimated disturbance test signals or generated signal obtained from the power system network simulator with thyristor-controlled switched capacitor (TCSC) compensator that has been developed for this purpose. In this research thesis, Root Cause Analysis based on fault tree technique is used to identify disturbances first and root cause of false trips of a protective relay which may lead in cascading to blackout. Once the critical root causes are identified, conventional mitigation measures have been used first and then blocking and unblocking functions and digital filters in view of increasing the reliability of the considered protection system are proposed. The placement of phasor measurement units (PMUs) in electric transmission systems has also gained much attention for enhancing the control as well as the protection scheme. In this research work, a binary teaching learning based optimization (BTLBO) algorithm for the optimal placement of phasor measurement units (PMUs) is proposed. The optimal PMU placement problem is formulated to minimize the number of PMUs installation subject to full network fault observability at the power system buses. The effectiveness of the proposed method is verified by the simulation of the IEEE14-bus