SOURCE:

Faculty: Engineering
Department: Electrical Engineering

CONTRIBUTORS:

Ezendiokwelu, C.E;
Ezechukwu, O.A;

ABSTRACT:

The Flexible Alternating Current Transmission System (FACTS) devices affect the performance of the pre-existing protective distance relays on the transmission line. These devices make the distance relay to either under reach or over reach their protection zone and trip boundaries especially when they are located within the fault loop. This dissertation dealt on the mitigation of the effects of a series FACTS device, Thyristor Controlled Series Capacitor (TCSC), on the distance relays used in the protection of transmission lines. The simulation model of the Thyristor Controlled Series Capacitor, a series FACTS device was implemented in the Nigeria power system using MATLAB/ Simulink software tool so as to bring to fore the impact of these compensation devices on the performance of distance relays on the transmission line. The apparent impedance of the Nigeria 330kV transmission network was calculated based on the symmetrical components of voltage and current. The results from the case system for different fault types at various locations were generated from system modelling and simulations for conditions without TCSC, with TCSC and with Metal Oxide Varistor (MOV) protection. For the case without TCSC, the relay tripped a 50km fault at 50.03km for relay A and 229.47km for relay B indicating zone 1 and zone 2 protection zone respectively. For a 100km fault, the relay tripped at 100.1km for relay A and 181.9km for relay B indicating zone 1 protection for both relays. Also for a 250km fault, the relay tripped the fault at 250.17km for relay A and 29.15km for relay B indicating zone 2 and zone 1 protection zone respectively. This base case without TCSC indicates that the distance relay operated accurately and tripped the fault at the correct protection zones. When TCSC was incorporated in the system under different fault conditions, the relay overreached its protection zone; for a 50km fault, the relay tripped the fault at 51.15km for relay A and 117.6km for relay B indicating both relays tripping in protection zone 1. For a 100km fault, the relay tripped at 100.1km for relay A and 67.46km for relay B. Also for a 250km fault, relay A tripped at 138.2km and relay B tripped at 30.02km indicating both relays tripping in zone 1. These tripping zones for TCSC incorporation show inaccurate relay zone coordination. The introduction of protective MOV with TCSC considering line distributed parameters resulted to further relay mal-operation. Implementing the developed adaptive relay algorithm, a 50km fault tripped correctly at 50.01km for relay A and 229.77km for relay B, 100km fault tripped at 100.1km for relay A and 180.01km for relay B also 250km fault tripped at 250.10km for relay A and 29.50km for relay B. These indicate correct and accurate protection zone tripping. Thus, the results from the developed adaptive relay algorithm proved very effective in adjusting the settings of the relay to accurately trip with respect to the location and direction of faults in the Nigeria power system.