Designing of Phase Angle control and ON-OFF Triggering circuit for SVC reactive Power Compensator.

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1 International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) Designing of Phase Angle control and ON-OFF Triggering circuit for SVC reactive Power Compensator. Mohammed Imran Assistant Professor [FACTS] EED Dept Muffakham Jah College of Engineering &Technology Hyderabad, India imraneed@mjcollege.ac.in Mohammed abdul khader aziz biabani [Power Electronics & systems] EED Dept Muffakham Jah College of Engineering &Technology Hyderabad, India azizbiabani009@gmail.com Abstract In this paper, to control the reactive power svc (Static Var Compensator) is used. The operation of SVC is depends upon two strategies. One is TCR (Thyristor control reactor) and other one is TSC (Thyristor switch capacitor). This two strategies is controlled by designing triggering circuit using single IC TCA 785. Depending upon varying load demand the svc can operates in both modes either TCR or TSC using same IC TCA 785 based triggering scheme. For the optimum solution for reactive power compensation the strategy control is adopted by using IC TCA 785. Both the control schemes is control by using one IC TCA 785, by this cost of the system will be reduced at domestic consumer level. Comparative and experimental results for the proposed SVC have been shown. Keywords Phase angle control, on-off triggering,svc compensator and IC TCA 785. I. INTRODUCTION The capacitors generate and reactors (inductors) absorb reactive power when connected to an ac power source. They have been used with mechanical switches for controlled var generation and absorption since the early days of ac power transmission. Continuously variable var generation or absorption for dynamic system compensation was originally provided by over-or under-excited rotating synchronous machines and, later by saturating reactors in conjunction with fixed capacitor. Since the high power, line-commutated thyristors in conjunction with capacitors and reactors have been employed in various circuit configurations to produce variable reactive output. These in effect provide a variable shunt impedance by synchronously switching shunt capacitors and/or reactors in and out of the network. Using appropriate switch control, the var output can be controlled continuously from maximum capacitive to maximum inductive output at a given bus voltage. More recently gate turn-off thyristors and other power semiconductors with internal turn-off capability have been used in switching converter circuits to generate and absorb reactive power without the use of ac capacitors or reactors. These perform as ideal synchronous compensators (condensers), in which the magnitude of the internally generated ac voltage is varied to control the var output. All of the different semiconductor power circuits, with their internal control enabling them to produce var output proportional to an input reference. A static var generator whose output is varied so as to maintain or control specific parameters (e.g. voltage, frequency) of the electric power system. Modern static var generators are based on high-power semiconductor switching circuits. These switching circuits inherently determine some of the important operating characteristics, such as the applied voltage versus obtainable reactive output current harmonic generation, loss versus var output, and attainable response time, setting limits for the achievable performance of the var generator and, independent of the external controls used, ultimately also that of the static var compensator. II. THYRISTOR-CONTROLLED REACTOR (TCR) An elementary single-phase thyristor-controlled reactor (TCR), it consists of a fixed (usually air-core) reactor of inductance L, and a bidirectional thyristor valve (or switch). Currently available large thyristors can block voltage up to 4000 to 9000 volts and conduct current up to 3000 to 6000 amperes. Thus, in a practical valve many thyristors (typically 10 to 20) are connected in series to meet the required blocking voltage levels at a given power rating. A thyristor valve can be brought into conduction by simultaneous application of a gate pulse to all thyristors of the same polarity. The valve will automatically block immediately after the ac current crosses zero, unless the gate signal is reapplied. III. THYRISTOR-SWITCHED CAPACITOR (TSC) A single-phase thyristor-switched capacitor (TSC) is consist of a capacitor, a bidirectional thyristor valve, and a relatively small surge current limiting reactor. This reactor is needed primarily to limit the surge current in the thyristor valve under abnormal operating conditions (e.g., control malfunction causing capacitor switching at a wrong time, when transient free switching conditions are not satisfied); it may also be used to avoid resonances with the ac system impedance at particular frequencies /16/$ IEEE 1

2 IV. AC PHASE ANGLE CONTROL AND BURST OR ON/OFF FIRING A. Working of Logic chip as AC Phase Angle Control: The operation and working of logic chip component for phase control application is One input is the short duration pulses of 30 micro sec (comparator output). To make the IC work as a Phase control firing circuit, the other input is the High frequency oscillation pulses from 555 astable multivibrator output. This input is connected to pin 6 of TCA 785. Thus, when the two inputs of logic are high the output goes high and it results in high pulsed pulses at pin 14 and pin 15 of TCA 785 IC and this circuit arrangement works as an AC phase control circuit. 3 QU Output U 4 Q2 Output 1 inverted 5 VSYNC Synchronous voltage 6 I Inhibit 7 QZ Output Z 8 V REF Stabilized voltage 9 R9 Ramp resistance 10 C10 Ramp capacitance 11 V11 Control voltage 12 C12 Pulse extension 13 L Long pulse 14 Q1 Output 1 15 Q2 Output 2 16 VS Supply voltage B. Working of Logic chip as Burst or ON/OFF Firing: The operation and working of logic chip component for ON/OFF firing application is One input is the short duration pulses of 30 micro sec (comparator output). To make the IC work as ON/OFF firing circuit, the other input is the low frequency oscillation pulses from 555 astable multivibrator output. This input is connected to pin 6 of TCA 785. Thus, when one inputs of logic is high and the other is low, the output goes low and it results in low pulsed pulses at pin 14 and pin 15 of TCA 785 IC and this circuit arrangement works as ON/OFF firing circuit. V. SIMULATION RESULTS The design and simulation results of reactive power compensation for AC phase angle control, Burst or ON/OFF firing and IC TCA 785 are presented in this paper. Design of Thyristor Gate firing circuit: IC TCA 785 pin description: TABLE 1 PIN SYMBOL FUNCTION 1 GND Ground 2 Q2 Output 2 inverted Fig.1 Designed Gate Friring Circuit Fig 1 shows the triggering circuit for 1-Ф AC voltage controller using IC TCA 785. The AC input signal v s is stepped down by the transformer and applied to pin 5. This signal serves as synchronization signal. The ramp voltage at pin 10 and the control and the control voltage at pin 11. In that pin 12 is connected to ground. Hence the firing pulses α to π is generated. Pin 6 is fed with inhibit pulses from 555 timer in astable mode. These pulses are applied at about 2kHz. Therefore the triggering signals generated on pins 14 and 15 are pulsed. The pulse pin 14 and pin 15 are passed only when 555 timer output is high. This results in pulse based drives for pulse amplifiers T 1 and T 2. The pulse amplifier T 1 generates firing pulses for SCR 2 firing pulses. The ramp resistor on pin 9 can be varied to vary firing angle(α). 2

3 Internal Description of IC TCA 785: C 12 V SYNC V S Fig.5 Generated Ramp Voltage at Pin 10 V 11 R9 V stab C10 Fig.2 Intetnal structure of IC TCA 785 Fig.6 Short duration Triggering pulses at pin 14 Fig.3 Pin 5 arrangements Fig.7 Short duration Triggering pulses at pin 15 AC Phase Control Firing Scheme Results: Fig.4 Input to Pin 5 3

4 Fig.8 Triggering pulses at α=90 for TCR. Fig.11 Expected waveform of astable 555 multivibrator Fig.12 Output at pin 3 of 555 timer circuit Burst or ON/OFF Firing Scheme Results: Fig.9 Triggering pulses at α=135 for TCR Astable 555 multivibrator: V CC R A V CC RB V 0 Fig. 10 Circuit of astable 555 multivibrator Fig.13 Triggering pulses from ON /OFF circuit 4

5 Observation for the Working model of SVC: capacitor value in µf Voltage (V) in volts TABLE 2 Current(I) in Amps Real power (MW) Reactive power(mvar) Fig 14 Firing angle equal to 90 degree with maximum conduction Firing angle (α) Voltage (V) TABLE 3 Current(I) Real power (MW) Reactive power(mvar) Fig 15 Firing angle equal to 120 degrees Experimental results for TCR: The following graphs obtained when oscilloscope was connected to the circuit when the TCR was fired at different angles. Channel one (CH1) is the voltage waveform across the thyristor. Channel two (CH2) is the reactor current waveform. Channel 3 (CH3) is the supply voltage waveform and channel four (CH4) is the thyristor current waveform. Fig 16 Firing angle equal to 165 degrees VI. CONCLUSION Depending upon the two modes of operation of SVC using single IC TCA 785, the simulations have been performed. In the AC phase angle control, the output results at different firing angle α are shown. And the burst or ON/OFF firing scheme of output waveforms are presented. Using one IC TCA 785, both the operations have performed. The best control strategy or scheme which is applicable for SVC reactive power compensation is used. References [1] B. Somanathan Nair. Digital Electronics And Logic Design, sixth printing September 2006.ISBN [2] Rajiv K. Varm R. Mohan Mathur. Thyristor-Based FACTS Controllers for Electrical Transmission Systems, volume 1. John Wiley and Sons, USA, febraury ISBN [3] Allan T Johns Yong Hua Song. Flexible AC Transmission Systems. The institution of Electrical Engineers, London, 199. ISBN

6 [4] N. G. Hingorani and L. Gyugyi. understanding FACTS Concepts and Technology of Flexible AC Transmission Systems, volume ISBN [5] Abhijit Chakrabarti and Sunita Halder. Power system analysis operation and control, 3rd edition New delhi, ISBN [6] Miller. Reactive power Control in Electric Systems. USA, ISBN [7] Hingroani Lasezlo Gyugyi Naraing G. Understanding facts. IEEE press, USA,2000. ISBN [8] U.A. Bakshi and V.U.Bakshi. Basic Electrical Engineering, 2nd revised edition SBN AUTHORS Mohammed Imran received his Bachelors in Electrical and Electronics Engineering from JNTU Hyderabad, AP, India in 2009 and Master s Degree M.Sc in Electrical Engineering from Staffordshire University, Stafford, England in 2011 respectively. He is working as an Professor teaching courses Electrical Machines, Industrial Electronic Systems, Power Electronics, Linear IC Applications in the Department of Electrical & Electronics Engineering, Muffakham Jah College of Engineering and Technology, Banjara Hills, Hyderabad, India, His research area of interests includes FACTS, Power Electronic Converters, Reactive power compensation techniques, and generations, power electronic, and Automation based Industrial Welding applications. Mohammed Abdul Khader Aziz Biabani is a Research student, [Power Electronic &Systems] of Electrical & Electronics Engineering department, from Muffakham Jah College Of Engineering & Technology, Affiliated to Osmania University Hyderabad, Telangana, India. Received his B.Tech degree in Electrical & Electronics Engineering from Jawaharlal Nehru Technological University Hyderabad, Telangana, India in His research interests include Power Electronic Systems, Power Systems, and Industrial Electronic Systems. 6