Torsional Resonance Identification in Turbine-Generator Shaft Due to the Operation of Electric Arc Furnaces at Steel Mills in Bangladesh Power System

Abstract

Many steel mills in Bangladesh use electric arc furnaces (EAFs) that can impact the generating units of the country's power system. The EAFs can cause power quality problems, such as the injection of the sub-synchronous frequencies (SSFs), which may be close to the torsional resonance (TR) frequency of the turbine generator shaft. As a result, the torsional oscillating torques may be amplified and pose a potential threat to the rotating shaft systems. This paper comprehensively investigates the torsional resonance caused by the operation of EAFs in the power grid. It simulates the power system of the Chittagong region with two steel mills with alternating current (AC) EAFs where the large power plants are represented with an equivalent generation at the Comilla-North point. The MATLAB simulation tools are used to model the threephase EAFs. To produce realistic characteristics of the EAFs, the resistances are modulated deterministically in the range of 1.20 to 45.5 Hz. Torsional mode frequencies in the turbine generator shafts are calculated using the Fast Fourier Transform (FFT) technique. The results show that the EAF operation amplifies the torsional oscillating torques in the turbine generator shaft. The turbine generator shaft in Raozan and Sikalbaha power plants exhibits a higher potential to be damaged because they are vulnerable to the potential threat of amplified torsional torques.