Two-folded implementation of a 12-pulse TCR with dissimilar transformers for a ladle furnace: reactive power compensation and power system redundancy

This paper is devoted to the design and implementation of a 12-pulse thyristor controlled reactor (TCR) system, which constitutes a low-cost solution to the reactive power compensation problem of a ladle furnace in Iskenderun iron and steel plant (ISDEMIR). Design objectives and elimination of 5th and 7th harmonic current components produced by 6-pulse TCRs are met by connecting two sets of 6 kV, 6 MVAr TCRs to the 34.5 kV ladle furnace bus by the use of two separate converter transformers with delta- and wye-connected secondaries. The effects of dissimilarities between the two sets of 6-pulse TCRs on the harmonic current content of the resulting 12-pulse TCR system are also presented in this paper. Both reactive power compensation and power system redundancy objectives are met by using two separate and dissimilar transformers instead of a single transformer with identical Δ-and Y-connected secondaries for connection to 6-pulse TCRs, resulting in a two-folded design. One of these transformers is chosen as a sufficiently large unit with two identical Δ-connected secondaries to supply the ladle furnace in emergency or during maintenance periods of main transformer. In normal operation mode of the resulting ladle furnace power system, the 12-pulse TCR implemented in the project gives quite satisfactory results in reactive power compensation and nearly meets harmonic standards currently used in the country.