Control Theory and Informatics www.iiste.org ISSN 2224-5774 (Paper) ISSN 2225-0492 (Online) Vol.4, No.7, 2014 15 Fuzzy Controlled SVC for Reactive Power Control of Long Transmission Lines Rekha 1 , Manmohan Kumar 2 , A.K.Singh 3 1. Assistant Professor, Dept. of EEE, NIT Jamshedpur, Jamshedpur, Jharkhand, India 1 2. PG Student [Power System], Dept. of EEE, NIT Jamshedpur, Jamshedpur, Jharkhand, India 2 3. Professor, Dept. of EEE, NIT Jamshedpur, Jamshedpur, Jharkhand, India 3 * E-mail of the corresponding author: rchy72@gmail.com Abstract Flexible AC transmission system (FACTS) devices are used to improve the existing transmission capabilities of the transmission system by making it more flexible and independent operating. The technology is used to achieve complete deregulation of power systems i.e generation, transmission and distribution. The loading capability of transmission system can also be enhanced nearer to the thermal limits without affecting the stability. The closed loop smooth control of reactive power can be achieved by using shunt connected FACTS devices. Static VAR Compensator (SVC) is one of the shunt connected FACTS device which is to be utilized here for the purpose of reactive power compensation. This paper attempts to design and simulate the Fuzzy logic control which is used to regulate the firing angle of SVC. With this scheme, it is seen that a better, smooth and adaptive control of reactive power has been achieved. The modelling and simulations are carried out for 750km long Transmission line and the compensation is placed at the receiving end (load end). Keywords: Flexible AC transmission system (FACTS); Static VAR Compensator (SVC); Fuzzy Logic Controller (FLC). 1. Introduction In power system, the reactive power generation and absorption is essential since the reactive power plays a vital role in keeping the voltage of power system stable. The main elements for generation and absorption of reactive power are transmission line, transformers and alternators. The transmission lines have distributed parameters throughout the line. On the light loads or at no loads, parameters become predominant and consequently the line supplies charging VAR (generates reactive power). In order to maintain the terminal voltage at the load bus adequate, reactive reserves are needed. FACTS devices like SVC can be used which helps in achieving better economy in power transfer. In this paper transmission line (λ /8) is simulated using 4π line segments by keeping the sending end voltage constant. The receiving end voltage fluctuations were observed for different loads. In order to maintain the receiving end voltage constant, shunt inductor and capacitor are added for different loading conditions. SVC is simulated by means of Fixed Capacitor and Thyristor Controlled Reactor (FC-TCR) which is placed at the receiving end. The firing angle control circuit is designed and the firing angles are varied for various loading conditions to make the receiving end voltage equal to sending end voltage. Fuzzy Logic Controller (FLC) is designed to achieve the firing angles for SVC such that it maintains a flat voltage profile. All the results thus obtained, were verified and were utilized in framing of fuzzy rule base in order to achieve better reactive power compensation for the transmission line (λ/8). Based on observed results for load voltage variations for different values of load resistance, inductance and capacitance; a FLC is designed which controls the firing angle of SVC in order to automatically maintain the receiving end voltage constant. 2. Modeling of SVC An elementary single phase thyristor controlled reactor [4] (TCR) shown in Fig.1 consists of a fixed (usually air core) reactor of inductance L and a two anti-parallel SCRs. The device brought into conduction by simultaneous application of gate pulses to SCRs of the same polarity. In addition, it will automatically block immediately after the ac current crosses zero, unless the gate signal is reapplied. The current in the reactor can be controlled from maximum (SCR closed) to zero (SCR open) by the method of firing delay angle control. That is, the SCR conduction delayed with respect to the peak of the applied voltage in each half-cycle, and thus the duration of the current conduction interval is controlled. This method of current control is illustrated separately for the positive and negative current cycles in Fig.2 where the applied voltage V and the reactor current i L (α) at zero delay angle (switch fully closed) and at an arbitrary α delay angle are shown. When α =0, the SCR closes at the crest of the applied voltage and evidently the resulting current in the reactor will be the same as that obtained