Analysis of Harmonic Characteristics in the Electrical System of Combined Cycle Power Plant (CCPP) at Tambak Lorok Block 2

Abstract

Non-linear loads are extensively utilized in various industries, including power generation. The use of non-linear loads is favored due to their high energy efficiency, but it leads to the emergence of harmonics in the power system source. One such example is the Gas and Steam Power Plant (PLTGU) at Tambak Lorok Block 2, located in Semarang, Central Java, Indonesia, which employs a three-phase full-wave AC/DC converter for the DC power system as the primary power source for DC generation equipment. Due to the high demand for DC power supply, a large-capacity three-phase full-wave AC/DC converter is required. The harmonics generated exhibit different characteristics depending on the type of non-linear load used. Therefore, a study is needed to model the electrical system and non-linear loads to understand the harmonic characteristics and values in the power generation electrical system. These results will be compared with the IEEE 519-1992 standard.

The equivalent approach results indicate that the use of the converter generates odd-order harmonics on the source side, in addition to multiples of three, with significant magnitudes of harmonic current. Furthermore, based on the equivalent electrical system approach using Matlab simulation, the Total Harmonic Distortion Index (THDI) at the 400V Essential Service PDC 4 busbar as the point of common coupling is found to be 16.65%, while the Psim simulation yields a THDI of 21.47%. Additionally, the THDI at the 400V Auxiliary Power Panel 11B busbar, according to Matlab, is 41.25%, and 42.23% according to Psim. These simulation results exceed the permissible harmonic percentage set by the IEEE 519-1992 standard. These harmonics have negative impacts, such as increased loading on induction motors, cables, and transformers, resulting in excessive equipment temperature and reduced lifetime. Furthermore, the effects of harmonic current also result in power losses in the auxiliary power equipment of the plant, which are dissipated as heat.