Vol.:(0123456789) 1 3 Journal of Electrical Engineering & Technology (2020) 15:2017–2026 https://doi.org/10.1007/s42835-020-00478-7 ORIGINAL ARTICLE Sub-synchronous Resonance Constrained OPF Using Reconciled Pack Dominance Based Grey Wolf Optimisation Devesh  Raj Mani 1  · Somasundaram Periasamy 2 Received: 3 January 2020 / Revised: 24 May 2020 / Accepted: 26 June 2020 / Published online: 3 July 2020 © The Korean Institute of Electrical Engineers 2020 Abstract In this paper, the Sub-synchronous Resonance Constrained Optimal Power Flow (SSRCOPF) problem is articulated, for stable and economic operation of series compensated power system. Further, Reconciled Pack Dominance based Grey Wolf Optimisation (RPD-GWO) is proposed to solve SSRCOPF problem. Due to the colossal increase in demand, transmission lines are stressed by overloading. To alleviate this stress, often series compensation by Thyristor Controlled Series Capacitor (TCSC) is used. However, due to unintended operation of TCSC there is a possibility of Sub-synchronous Resonance (SSR). Hence, SSR constraint is infused into Optimal Power Flow (OPF) and termed as SSRCOPF. The proposed SSRCOPF ensures optimal system operation, while circumventing the entrapment into SSR condition. To solve the SSRCOPF problem the proposed RPD-GWO algorithm is employed and analysed with Particle Swarm Optimisation (PSO). The comparative analysis of proposed RPD-GWO algorithm reveals its swiftness in convergence. Keywords Grey wolf optimisation · Optimal power fow · Sub-synchronous resonance · Thyristor controlled series capacitor 1 Introduction The primary motives of Energy Management System (EMS) are to provide an economic schedule to generating units along with stable power system operation. This is achieved by solving the Optimal Power Flow (OPF) [1], which mini- mizes the cumulative fuel cost along with due consideration of bus voltage and line fow limits. In the state-of-art, power system encounters massive increase in power demand, thus provoking added challenges to EMS. One such challenge is to transfer excess power to load centres from generating units using the existing transmission system (with inade- quate power transfer capacity). This challenge is efectively resolved by series compensation in lines using Thyristor Controlled Series Capacitor (TCSC). Thus the placement of TCSC in transmission line, enhances load carrying capacity, improves system stability and controls load sharing between lines [2]. Under transient conditions, TCSC compensated line in the vicinity of steam turbine-generator is vulnerable to torsional oscillations [3, 4] due to energy exchange in electro-mechanical systems. The rotor in a steam turbine- generator is a complex structure with diferent masses con- nected to a shaft. When the system is perturbed, torsional oscillations occur in rotor shaft between the masses. These torsional oscillations are characterized by natural frequen- cies (below synchronous range). This torsional oscillation attain intolerable value, if the natural frequency of TCSC compensated line is equal to any one of the tortional fre- quencies. This critical stability issue is termed as Sub-syn- chronous Resonance (SSR) [5]. This immense oscillation (due to SSR) leads to permanent shaft damage. Thus to avoid the possibility of SSR occurrence there is a need to incorporate adequate constraint in OPF. Hence, in this paper OPF is incorporated with SSR constraint, thus appropriately termed as Sub-synchronous Resonance Constrained Optimal Power Flow (SSRCOPF). In the SSRCOPF, TCSC is mod- elled as a variable series reactance [2, 3] and the degree of compensation in TCSC incorporated line is considered as additional control parameter. Eigen value analysis [3, 4] is used to identify the SSR occurrence. The SSR condition is * Devesh Raj Mani deveshraj.m@gmail.com 1 Department of Electrical and Electronics Engineering, SSN College of Engineering, Chennai, Tamil Nadu, India 2 Department of Electrical and Electronics Engineering, College of Engineering Guindy, Anna University, Chennai, Tamil Nadu, India