APPLICATION OF AN OPTIMAL TUNING TECHNIQUE OF ON-LOAD TAPCHANGING TRANSFORMER FOR POWER QUALITY IMPROVEMENT IN TRANSMISSION LINE NETWORK

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Department of Engineering

ABSTRACT
For reliable and efficient operation of power system, voltage level and reactive power flow along transmission lines has to be adequately regulated. To control reactive power flow over transmission lines and compensate for varying voltage drops, tap changing transformers are required. By altering the voltage magnitudes at the windings of the transformers through winding tap adjustment, reactive power flow can be controlled. The transformers can be off-loaded or on-line tap changer. In the latter, the transformers are disconnected from the system when the tap setting is to be adjusted, while in the former, the tap adjustment is carried out with the transformers connected. In this research work, Grey Wolf Optimization (GWO) algorithm is applied to determine the optimal On-Line Tap Changer (OLTC) of the available transformers in the system in order to improve the voltage profile and regulate reactive power. The constraints considered in the formulation of the problem are demand-generation balance, bus voltage limits, line thermal overloading limits and tap-changer adjustment limits according to IEEE C57.131 2012 requirement. To verify the effectiveness of the developed technique, it is implemented on IEEE 14-bus, IEEE 30-bus and 57-bus Nigerian Transmission systems. The performances of the proposed technique is compared with those obtained using Particle Swarm Optimization (PSO). From the simulation carried out in MATLAB environment, it is observed there is significant reductions in the overall voltage deviation (VD) as well as the reactive power loss (RPL) when the OLTCs are optimized. For instance, in the IEEE 14-bus system, the VD was reduced from 2.0892pu (base case) to 1.0153pu due to the optimal tuning of the OLCTs using GWO and 1.4783pu when PSO was applied. This represents 51.40% improvement in the case of the developed GWO over that of the base case and 31.32% improvement over the case of the PSO. Similarly, the RPL was reduced from 277.298MVar of the base case value to 156.542MVar due to the optimal tuning of the OLCTs using GWO and 206.591MVar when PSO was applied representing 43.54% and 25.49% improvements respectively. These have demonstrated the applicability of the GWO and its superiority over PSO in optimizing the OLTCs in the IEEE 14-bus and 30-bus systems. In the Nigerian 57-bus system, by applying the GWO, the total VD was reduced from 6.7808pu (base case) to 4.4519pu representing 34.35% improvement. Finally, the value of RPL was reduced by 36.56% from its original value of 185.4685Mvar.