Analysis and Simulation of Filters for Reduction of Harmonics in Large Electrical Network

Abstract

Nowadays, the concern about power quality is continuously increasing due to the automation in industry and extensive use of non-linear devices in power system. These non-linear control devices or non linear loads are the major sources of harmonics. The operation of non linear devices or non linear loads distort to the current waveform. Such distortion affect the quality of power and this will cause malfunction to the sensitive devices such as metering instruments, online process analyzers and measuring devices then false readings may be displayed. These false readings are going to affect the operation of the plant and may cause shut down and large monetary losses. This will result into poor quality of the product. This project covers the harmonic analysis of 220MW IOCL petrochemical plant. This 220 MW Petrochemical plant with a captive grid has sixteen processing units. In this plant, generation of electric power is at 11 KV and distribution is at 33kV/ 6.6kV/415V. It has various loads having voltage rating of 11kV/6.6kV/415V. The plant consists of large number of semiconductor equipments viz uninterruptable power supplies, variable frequency drives, battery chargers, etc. These non linear loads generate harmonics which result into distortion of source current. The work includes the modeling of whole plant and its harmonic analysis in ETAP software. The selection of filter topology and its design is based on the outcome of modeling and analysis. This output report identifies the harmonic generating points, total harmonic distortion at that point, the load connected to that point etc. The simulation of filters to mitigate the harmonics is done using MATLAB software. The work also include variable hysteresis band current controlled active power filter topology to mitigate the variation of switching frequency problems that encountered in fixed hysteresis band current controlled active power filter. From the simulation results the selected filters are successively able to mitigate the harmonics generated in the plant and improve the power quality as well as the product quality.