SECURED THIRD ZONE PROTECTION UNDER STRESSED CONDITIONS OF TRANSMISSION SYSTEM

Abstract

Transmission line protection is an essential component for the reliable and secure operation of the power transmission network. Distance Relays (DRs) are commonly used to protect transmission lines due to their benefits over the overcurrent relays. However, under severe stressed situations (such as power swing, load encroachment, and voltage instability), the distance relay may maloperate due to encroachment of the locus of the positive sequence impedance into the third zone operating characteristics. Malfunctioning of DRs can cause cascade tripping in the power transmission network, resulting in power system blackouts. In distance protection, due to balanced nature, it is difficult to distinguish symmetrical faults from severe stressed situations. In order to prevent malfunctioning of DRs, conventional power swing blocking techniques have been utilized. However, these schemes may fail to block the trip signal under fast power swing situations. Further, the timer setup is complicated and fault detection during power swing conditions is challenging. To address the limitations of conventional methods, several techniques for blocking trip signals during severe stressed conditions on various types of transmission network (uncompensated, series compensated, and wind integrated) are suggested in this thesis. The initial stage of the research is related with the development of an algorithm for preventing DR maloperation during severe stressed circumstances, as well as precise differentiation between symmetrical faults and severe stressed situations on power transmission network. The proposed scheme is based on comparison of phase angle of superimposed positive sequence component of current with a preset threshold. The threshold value is decided by performing various simulations on standard test systems along with appropriate validation through analytical analysis. The performance of the proposed scheme has been evaluated on different faults and severe stressed conditions by modeling IEEE-14 and IEEE-39 bus test systems in Real-Time Digital Simulator (RTDS/RSCAD) environment. The threshold value utilized in the presented technique remains almost same for transposed/untransposed and uncompensated/compensated transmission networks. Thereafter, a protection scheme for a series compensated transmission line, which prevents maloperation of DRs during severe stressed conditions, is presented. The suggested method depends on the calculation of the net angular difference of positive sequence phasors of voltage and current signals acquired from Phasor Measurement Units (PMUs). For fully observable power system network, the minimum number of PMUs required with a maximum number of system observability redundancy index has been identified by the suggested method using binary chemical reaction optimization technique. The validity of the suggested technique has been confirmed by generating different severe stressed conditions along with faulty situations by modelling IEEE-39 bus system using RTDS/RSCAD software. The suggested technique offers effective discrimination between severe stressed conditions (symmetrical/asymmetrical power swing, load encroachment, voltage instability) and faulty situation even against wide variation in fault type, fault resistance, fault inception angle, degree of compensation and location of the series capacitor (middle or both ends of the line). Integration of wind-based renewable energy sources into long Extra High Voltage (EHV)/Ultra High Voltage (UHV) uncompensated/compensated power transmission network poses significant problems in terms of proper detection of power swings and effective discrimination between symmetrical faults and power swing situations. As the existing protection strategies are unable to detect the said circumstances, a technique based on the difference between sending end and receiving end positive sequence current angles of the transmission line is proposed. The required data is collected with the help of PMUs placed on both sides of the line. The scheme results in effective discrimination between distinct faults and circumstances of asymmetrical/symmetrical power swing and achieves satisfactory outcome during current transformer saturation condition. The suggested algorithm has been evaluated on the wind-integrated IEEE-9 bus system by producing power swings, various cases of fault, and faults during power swing. Validation of the suggested technique was carried out by the execution of Hardware-in-Loop (HIL) simulation on RTDS. The achieved outcomes disclose higher sensitivity and better discriminating ability of the presented technique compare to the existing approaches. After that, an algorithm to discriminate between in-zone fault and out-of-zone fault conditions under power swing scenarios for wind/synchronous generator (WG/SG) integrated power transmission networks is proposed. The proposed algorithm is based on the calculation of positive sequence power loss index of the transmission line, which is obtained by taking absolute difference of calculated and measured value of positive sequence real power loss. The authentication of the suggested technique is verified by performing HIL simulation in RTDS framework along with physical PMUs, Phasor Data Concentrator (PDC) and voltage and current amplifier. Various events such as power swing, in-zone (including close-in and high resistance) fault during power swing and out-of-zone fault during power swing are simulated by modeling WG/SG integrated IEEE-9 bus power transmission system in RSCAD frame work. Impact of noise and CT saturation phenomena on the proposed algorithm is also analyzed. The proposed algorithm offers accurate discernment between in-zone and out-of-zone faults during power swing conditions. The accomplished results reveal increased sensitivity and improved distinguishing capability of the proposed algorithm in contrast with those of many other approaches proposed in the literature. The study described here is anticipated to make a substantial contribution to transmission line protection. Various approaches proposed will be especially beneficial for uncompensated/series compensated, transposed/untransposed, and wind integrated power transmission networks.