International Journal of Advance Engineering and Research Development (IJAERD) ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406 Modelling of Reactive Power & Unity Power Factor Control of Inductive Load Nirvisha V. Vyas1, Nitin H. Adroja2, Ashish Doorwar3 1 PG student, 2,3Asst. Professor, Electrical Engineering Department, Atmiya Institute of Technology & Science, Rajkot 1 nirvisha.vyas@gmail.com 2 nhadroja@aits.edu.in 3 ashish.doorwar@gmail.com Abstract— TSC-TCR (SVC) is applied to control power factor of system at unity & effectively regulate load voltage. Unity power factor controller uses SVC technique, whose output is adjusted to exchange capacitive or inductive current so as to maintain or control specific power factor. In this proposed scheme simple circuit model of thyristor switched capacitor & thyristor controlled reactor is modeled. The number of capacitors to be turned-on is decided according to the reactive power requirement of load. The current delivered by the capacitor depends on the reactive power requirement. that cosᴓ2 is greater than cosᴓ1 and hence power factor of the load is improved [1]. This is shown in the following phasor diagram. Keywords - firing angle, reactive power, SVC, TSC-TCR. I. INTRODUCTION This paper deals with the description of power factor, analysis and counter measures of power factor and mitigation techniques are also explained. Modern power system is complex and it is essential to fulfil the demand with better power quality. Advanced technologies are now a day being used for improving power system reliability, security and profitability and due to this power quality is improved. Voltage stability, voltage security and power profile improvement are essential for power quality improvement. Low power factor produces large copper losses, poor voltage regulation and reduce handling capacity of the system. At low power factor KVA rating of the equipment has to be made more, making the equipment larger and expensive [1]. Power factor improvement is important because at high, medium and low power factor the current distortion levels tends to fall into low THD≤20%, medium (20%<THD≤50%) and high (THD>50%) respectively [2]. Low power factor can be improved by static capacitors [4], synchronous condenser, and phase advancers [1]. In this paper power factor has been improved automatically by using microcontroller with static capacitors & reactor. II. POWER FACTOR IMPROVEMENT THEORY The low power factor is mainly due to the fact that most of the power loads are inductive and therefore, take lagging currents, so capacitors are connected in shunt at the load end for injecting leading power. It draws current I c which leads the supply voltage by 90ᵒ. The resulting line current I1 is the phasor sum of I and IC and at an angle of ᴓ2 as shown in fig. 1(c). It is clear that ᴓ2 is less than ᴓ1 from phasor diagram. So @IJAERD-2014, All rights Reserved Fig. 1 (a)-Inductive load (b)-Capacitor with load (c)-phasor diagram A. Available Devices for Power Factor Correction To achieve optimum performance of power system it is required to control reactive power flow in the network. Voltage collapse occurs in power system when system is faulted, heavily loaded and there is a sudden increase in the demand of reactive power. Reactive power balance can be regained by connecting a device with the transmission line which can inject or absorb reactive power based on system requirement. FACTS are a family of devices which can be inserted into power grids series, in shunt, and in some cases, both in shunt and series for reactive power compensation & hence for unity power factor control. Available facts devices are: 1) Shunt Device Static VAR Compensator Static Synchronous Compensator (STATCOM) 2) Series Device Thyristor Controlled Series Compensator (TCSC) Static Synchronous Series Compensator (SSSC) B. Different Methods for power Factor Correction There are mainly three types of techniques for power factor correction. 1) Synchronous Alternators 2) Static VAR Compensators (SVC) 1 International Journal of Advance Engineering and Research Development (IJAERD) ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406 3) Banks of Static Capacitors Distributed power factor correction Group power factor correction Automatic power factor correction In TSC capacitor is connected in series with anti-parallel connected thyristor. By controlling turning ON & turning OFF of the thyristor control reactive power delivered. This is shown in fig 3. III. PROPOSED SCHEME Zero crossing of voltage & current of the system is measured & it is given to micro-controller to generate appropriate gate pulses as shown in fig.2. According to the generated gate pulses, number of capacitor is on. To provide proper compensation reactor is on after turning on number of capacitor so that power factor can be maintain at unity [5]. Fig. 3 Switching of capacitor Fig. 2 Basic unity power factor system A. Switched capacitor 1) Switching Technique: To avoid transients at the moments of connecting capacitors, their voltage as well as sign must be equal to that of the line. Moreover, the slope of variations of line voltage must be equal to zero; that is, dVL(t)/d(t) = ic(t)/c = o , where VL (t) is the line voltage (the series low impedance inductor is ignored) and c is the capacity of a TSC branch. To disconnect a capacitor from the line, sending firing signals to the relevant thyristor gate will stop. When the current value through a capacitor passes by zero, the thyristor turns off and leaves the capacitor charged to the line peak voltage. To avoid the capacitor to discharge in long periods of time due to its own and also its peripheral circuit leakage, firing pulses are sometime employed to the thyristor gate around the voltage peak time. Fig. 4 Voltage & Current waveforms of switched capacitor B. Firing of Reactor Firing of thyristor can be done according to the load requirement & reactive power absorbed by the capacitor. Here reactor is connected in series with anti-parallel thyristor as shown in fig. 5[6]. 2) Change of Polarity: Technically and also economically considering, the best capacitors for use in switching are AC capacitors. However such capacitors cannot tolerate large DC voltages for a long period of time [2]. In a TSC system, those capacitors that are not connected to the line have fixed voltages and having changed their polarity periodically, and therefore, put them under a low frequency AC voltage. To achieve this, as shown in fig. 3, connect the capacitor to the AC voltage line for only half a cycle. Here inductor is connected in series with capacitor to control high inrush current. @IJAERD-2014, All rights Reserved Fig. 5 Firing of reactor IV. CONTROL STRATEGY Basic scheme for power factor correction is shown in fig.6. Here AC supply of load is fed to the transformer; this will step down the voltage. Zero crossing of voltage & current is 2 International Journal of Advance Engineering and Research Development (IJAERD) ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406 sensed by zero crossing voltage & current detector respectively .This phase difference decide firing angle of thyristor switched capacitor. This signal is generated by the microcontroller. Reactor firing depends on the number of capacitor to be on & reactive power required by the load. Control scheme for generating switching signal & maintaining power factor at unity. Power Supply 1) Simulation Results Load Voltage Sensor Current Sensor Control circuit Zero Crossing Detector Micro Controller Gate driver Circuit Capacitor and Inductor Bank Anti-parallel Thyristor Fig. 8 Waveforms of open loop system The reactive power required to compensate the reactive power & make power factor at unity can be calculated by using the following equation [5]. Fig. 6 Control scheme for unity power factor V. OPEN LOOP CONTROL Inductive load is connected with power supply of 230 volt is shown in fig.7. Due to this inductive load power factor of the system is 0.91 lagging and active power & reactive power is 10000 watt & 4300 VAR. A. Without TSC-TCR + -i Vac Cu Continuous powergui Voltage Measurement P,Q pf +v - Scope5 Subsystem V 1 PQ pf I Scope2 Active & Reactive Power .........................................(1) Where, VAR = capacitor unit VAR rating C = capacitor (farads) f = frequency (cycles/second) Vr = capacitor unit rated voltage From this equation, calculate the reactive power of capacitor to compensate the lagging power factor of inductive load. According to the theory of power factor controller the capacitor add leading current to the lagging current and resultant current phase is less than the phase angle of previous inductive current. As power factor is cosine of this angle, power factor is also increases. To correct power factor at unity, capacitor of appropriate reactive power is fed using in eq. (1). By calculation the value of capacitor is 4280 VAR. B. Power Factor Correction With TSC Power factor correction by placing capacitor in shunt with load is shown in fig. 9. Scope4 Fig. 7 Open loop control of power factor controller @IJAERD-2014, All rights Reserved 3 International Journal of Advance Engineering and Research Development (IJAERD) ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406 + -i + -i Cu2 Cu2 Scope1 Scope2 Scope2 V V PQ PQ Scope1 I a g Sequence Thy5 k k k a Active & Reactive Power2 Thy4 Repeating Thy3 g k Thy2 a g k a g k g Vac a a Thy1 Thy5 k a Thy3 g Active & Reactive Power2 a g Repeating Thy4 Sequence g Thy2 k a g Thy1 AC Voltage Source1 k a k g I P,Q pf P,Q pf Scope4 Subsystem4 Scope4 Subsystem4 +v - +v - Voltage Measurement1 Voltage Measurement1 Continuous C1 C1 powergui Subsystem3 Continuous Subsystem3 Logical Operator1 Logical Operator1 powergui Fig. 9 Open loop system with capacitor Fig. 11 Open loop system with capacitor & reactor 1) Simulation Results for Power Factor Corrector: 1) Simulation Results for Power Factor Corrector & Reactive Power Controller: Fig.10 Waveform of close loop system For variable load, reactive power requirement changes to compensate the low power factor problem. So this circuit can not be usefull for variable inductive load. For that continous measurement & calculation of reactive power is required. This is the limitation of this sheme. fig. 10 shows the waveforms of corrected supply voltage and current & reactive power when capacitor is connected in shunt with load. C. Power factor & Reactive Power Correction With TSCTCR @IJAERD-2014, All rights Reserved Fig.12 Waveform of close loop system with reactive power 4 International Journal of Advance Engineering and Research Development (IJAERD) ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406 VI. CLOSED LOOP CONTROL For close loop system, continuous measurement of the reactive power requirement of variable load is required. As shown in fig. 12, power factor corrector that can supply reactive power up to 6000 VAR is presented. Each capacitor provides power of 2000 VAR System is designed for variable load. According to the requirement of the load number of capacitors is on. Here working flow of the scheme is present for each capacitor having capacity of providing 2000 VAR. reactive power control shunt inductor is required. By using TSC-TCR technique power factor & reactive power consumption of load can be improved. REFERENCES [1]. [2]. [3]. [4]. [5]. [6]. V.K Metha and Rohit Mehata,“ Principles of power system”,S. Chand & Company Ltd, Ramnagar, Newdelhi-110055,4th Edition,Chapter,6. W.Mack Grady and Robert J. Gilleskie, “Harmonics and how they relate to power factor”, Proc.Of the EPRI power quality issues & opportunities conference (PQA’93), San Diego,CA,November 1993. Coso, “Calculation of reactive power needed for the power factor of given system.” a precise catalogue, published by khawaja electronics pvt. ltd. manufacturing of fuji capacitors in lahore, pakistan, 1994. Technical Application Paper No: 8, “Power FactorCorrection and Harmonic Filtering in Electrical Plants”, ABB, Bangalore, 2010 Nader Barsoum,“Programming of pic microcontroller for power factor correction.” School of Engineering, Curtin University of Technology, Sarawak, Malaysia 2007 Md. Shohel Rana, Md. Naim Miah & Habibur Rahman, “Automatic Power Factor Improvement by using Microcontroller” Double Blind Peer Reviewed International Research Journal, Global Journals Inc. (USA), Volume 13 Issue 6 Version 1.0 Year2013. Fig. 13 Flow chart of proposed scheme VII. CONCLUSION This paper shows an efficient & economic technique to control power factor of the load. To improve power factor of load, only shunt capacitor or static capacitor are used. But for @IJAERD-2014, All rights Reserved 5