• No results found

Investigation of Effect of Harmonics on Voltage Stability in a Grid System by SVC

N/A
N/A
Protected

Academic year: 2020

Share "Investigation of Effect of Harmonics on Voltage Stability in a Grid System by SVC"

Copied!
5
0
0

Loading.... (view fulltext now)

Full text

(1)

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)

116

Investigation of Effect of Harmonics on Voltage Stability in a

Grid System by SVC

Gaurav Shrivastava

1

, Prof. S. K.Tripathi

2

, Prof. Sunil kumar Goel

3 1M.Tech Student, Power Electronics & Drives, K.I.E.T, Ghaziabad, India 2Associate Professor, Electrical & Electronics Engineering, K.I.E.T, Ghaziabad, India 3

Professor, Electrical Engineering, Meerut Institute of Engineering &Technology, Meerut, India

Abstract—This paper investigates the role of Static Var Compensator (SVC) on stability of voltage in grid system due to the presence of harmonics..Here the design of SVC is based on the combination of Thyristor switched capacitors (TSC’s) and Thyristor controlled reactor (TCR) . TSC’s are used for switching the capacitor banks on and off while the TCR continuously controls the reactive power by varying the current amplitude flowing through the reactor.But harmonics are induced in grid system due to TCR.In this paper FACTS controller such as Static Var Compensator is used to maintain the system voltage within limit by minimizing the harmonics internally. It is proposed to develop SVC with firing angle controller for 220KV,100 MVA transmission system. Proposed work is aimed at mathematical modeling of svc,development of control strategy and investigations of the performance of control strategy using MATLAB/SIMULINK.

Keywords— {Flexible a.c.transmission system (FACTS),

Static var compensator(svc), Thyristor controlled

reactor(TCR), Thyristor switched capacitor(TSC), Power electronics, Thyristors etc}.

I. INTRODUCTION

Now a days,the power systems are very unsecure due to the voltage instability problems because of large transmission networks having many generating stations, buses and different types of load patterns and deregulaton of the electricity industries.Due to the lack of reactive power support,the power system is becoming more vulnerable and leads to voltage collapse.So reactive power compensation is very much essential to maintain the system voltage within limit.This task is accomplished by FACTS Controllers[1] that improves the overall performance of the power system.

Shunt Facts controllers such as Static Var

Compensator(SVC) controls the system voltage effectively by adjusting the reactive power output at the connection point[3].

The primary objectives of a shunt compensator in the grid system are as follows :-

*It improves the load power factor nearly unity so that current drawn from the source will be in phase with the system voltage.

*Suppression of harmonics in load so that current drawn should be sinusoidal,

*Voltage regulation for the loads that cause fluctuations in the supply voltage.

*Cancelation of the effect of unbalance loads so that the current drawn from the source should be balanced (load balancing).

II. STATIC VAR COMPENSATOR

Static var compensators, regarded as the first FACTS controllers, have been used in North American transmission systems since late 1977 in western Nebraska [6].

According to definition of IEEE PES Task Force of FACTS Working Group: [3]

Static Var Compensator: A shunt connected static var generator or absorber whose output is adjusted to exchange capacitive or inductive current so as to maintain or control specific parameters of the electrical power system (typically bus voltage).

In general, an SVC is a combination of

Thyristor-Controlled Reactor(TCR), and Thyristor-Switched

Capacitor (TSC) .

A- BASIC DESCRIPTION OF TCR AND TSC

(2)

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)

117 When the load is inductive (lagging), the TSC activates and automatically switch on the capacitor banks to provide reactive power to make system voltage high[1]. Thus in both the conditions the system voltage remains with in limit.

III. CONTROL SCHEME

The control system having different units is described as follows,

(a). Measurement system- The positive sequence voltage which is to be controlled is measured by measuring unit.A fourier based measurement system that uses a one-cycle running average is used.

(b). Voltage regulator - It is the main unit of SVC controller.This unit determines SVC susceptance B in order to keep system voltage constant.To determine the susceptance B ,the voltage regulator uses voltage error which is the difference between the measured voltage (Vmeas.) and reference voltage (Vref.).

(c). Distribution unit- The firing angle alpha for TCR is computed by this unit and it also determines number of TSC‟s that switches the capacitor banks on and off automatically.

(d).Synchronizing unit- This unit has a Phase locked loop which is synchronized at the secondary voltage level and pulses to the thyristors is sent by pulse generator.

Fig-1.Voltage regulator

Fig- 2. Distribution Unit

Figure-2, shows the distribution unit that determines the firing angle alpha for TCR by using primary susceptance Bsvc which is computed by voltage regulator.The firing

angle α as a function of TCR susceptance can be

implemented by a look-up table by the equation

,

= ……….(1)

Where is the TCR susceptance in pu of rated TCR

reactive power .

TABLE- I

The parameters taken for simulation are as follows:-

Parameter Value

TCR branch Inductance 18.7 mH

TSC branch Capacitance 308.4μF

TSC branch Inductance 1.13mH

Hysterisis- distribution unit 0.1 (pu/100MVA)

Transformer nominal power 2000MVA,50HZ

Transformer total leakage 0.15 (PU/Pnom.)

Nominal secondary voltage 11KV(rms,ph-ph)

Kp 60

Ki 1400

A- FIRING UNIT

(3)

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)

[image:3.612.321.562.110.276.2]

118 Fig- 3.Firing Unit

IV. TEST SYSTEM MODEL

In this paper a 300-Mvar Static Var Compensator system is designed that regulate voltage on a 100-MVA, 220-kV system of frequency 50 hz.. The SVC consists of a 220kV/11kV, coupling transformer, of 333-MVA,one controlled Reactor bank and three Thyristor-switched Capacitor banks that are connected on the secondary side of the transformer.The main advantage of SVC system connected on transformer‟s secondary is that it reduces the size and number of components required in the SVC system. The simulink model of the test system is shown in figure 4.For the simulation purpose the SVC is kept in the voltage control mode and its reference voltage is set to Vref =1.025 p.u..First of all in Case -1,when no harmonic is induced in the system then analysis is done in

Case-2,when 3rd harmonic is induced and Case-3,when 5th

harmonic is induced.The simulation results show the effect of harmonics injection by TCR on system voltage.

Fig -4.Simulink model of Test System

Fig -5. Measurements across SVC ,TSC’s and Load

V. SIMULATION RESULTS

[image:3.612.52.294.136.372.2]

Case- A:THD of Grid voltage when no harmonic is induced This figure shows the T.H.D analysis of grid voltage when no harmonic is induced in the system.From this analysis we conclude that SVC controller is working properly and it maintains the system voltage within limit.

Fig- 6. THD of grid voltage

Case-B: When 3rd harmonic is induced

This figure shows the waveforms when 3rd harmonic is

[image:3.612.325.570.388.558.2] [image:3.612.51.290.608.690.2]
(4)

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)

[image:4.612.60.396.97.572.2]

119 Fig -7. Waveforms of SVC when 3rd harmonic is induced

Fig -8. THD of grid voltage at 3rd harmonic

Fig -9.THD of secondary voltage at 3rd harmonic

The T.H.D waveforms shows that SVC Controller is working logically in a proper manner.

Case-C: Waveforms when 5th harmonic is induced

This figure shows the effect of 5th harmonic injection in

the system due to TCR.The waveforms shows that there is no much effect of harmonic injection on the secondary voltage.

[image:4.612.324.570.250.556.2]

Fig-10. Waveforms of SVC when 5th harmonic is induced

Fig-11. THD of grid voltage at 5th harmonics

Fig -12.THD of secondary voltage at 5th harmonic

The T.H.D analysis and waveforms shows that secondary voltage is sinusoidal in nature and there is no much effect of harmonics on secondary voltage.

VI. CONCLUSION

[image:4.612.48.296.251.567.2]
(5)

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 6, June 2014)

120 The secondary voltage is sinusoidal in nature so it proves that the svc controller is working well in all the disturbing conditions.The current across load is in phase with load voltage that makes it closer to unity power factor. So it greately improves the quality of electrical power in grid system. Also, this system has continuous control and regulation from inductive to capacitive, and the response time is faster.

REFERENCES

[1] Narain G. Hingorani and Laszlo Gyugyi, “Understanding FACTS:

Concepts and Technology of Flexible AC Transmission

Systems”,Wiley IEEE Press, December 1999.

[2] L. Gyugyi, K.K. Sen and C.D. Schauder, “The interline power flow

controller concept: a new approach to power flow management in

transmission systems”,IEEE Transactions on Power Delivery, Vol.

14, No. 3, July 1999, pp. 1115-1123.

[3] “Static Var Compensator Models for Power Flow and Dynamic

Performance Simulation”, IEEE Special Stability Controls Working Group, IEEE Trans. on Power Systems, Vol. 9, No. 1, Feb. 1994.

[4] R. Mohan Mathur and Rajiv K. Varma. Thyristor-based

FACTScontrollers for electrical transmission systems. IEEE Press, Piscataway,2002

[5] Chopade, P.; Bikdash, M.; Kateeb, I.; Kelkar, A.D., "Reactive power

management and voltage control of large Transmission System using SVC (Static VAR Compensator)," Southeastcon, 2011 Proceedings of IEEE , vol., no., pp.85,90, 17-20 March 2011.

[6] A-A. Edris, Chair, “Proposed Terms and Definitions for Flexible AC

Transmission Systems (FACTS)”, paper prepared by the FACTS Terms & Definitions Task Force of the FACTS Working Group of the DC and FACTS Subcommittee, IEEE Trans. on Power Delivery, Vol. 12, No. 4, Oct. 1997, pp. 1848-1853.

[7] Pali, B.S.; Bhowmick, S.; Kumar, N., "Power flow models of static

VAR compensator and static synchronous compensator," Power India Conference, 2012 IEEE Fifth , vol., no., pp.1,5, 19-22 Dec. 2012.

[8] M.H. Haque, “Damping improvement using facts devices”.

Electrical Power Syst. Res.Volume 76, Issues 9-10, June 2006.

[9] K.R. Padiyar, "Novel FACTS controllers for system

improvement",Transmission & Distribution in 2000 Technical Conferences February 1996. pp. 6 - 8.

BIOGRAPHIES

Gaurav Srivastava: Pursuing M.Tech in “Power Electronics & Drives” from Krishna Institute of Engineering &Technology, Ghaziabzd. His area of interest is Power electronics, FACTS and Control system.

(„gauravsri005@gmail.com‟)

Prof. S. K. Tripathi: Working as an Associate Professor in the Department of Electrical and Electronics Engineering, Krishna Institute of Engineering and Technology, Ghaziabad.His area of interest is power electronics and drives.

(„surendra.27n@gmail.com‟)

Prof. S. K. Goel: Working as a Professor in Electrical Engineering, Meerut Institute of Engineering & Technology, Meerut since 1999.He has more than 25 years of experience in Industry and Teaching. He has worked in several industries, in both public and private sector. His area of interest include Electrical machines, Power system, FACTS.

Figure

Fig- 6. THD of grid voltage
Fig -8. THD of grid voltage at 3rd harmonic

References

Related documents

It was decided that with the presence of such significant red flag signs that she should undergo advanced imaging, in this case an MRI, that revealed an underlying malignancy, which

The relatively high intake of flavonoids in the investigated population of 50−year−old inhabitants of Wrocław resulted from a high consumption of black tea (daily consumption of

in a Case Previously Reported as "Nutritional Anemia in an Infant Responding to PERNICIOUS ANEMIA IN AN EIGHT YEAR OLD GIRL: Additional

Variations in the concentration of elements in plant samples of the tunnel #504 on the sampling profi le Analysis of the results suggests that the point with the highest

In this present study, antidepressant activity and antinociceptive effects of escitalopram (ESC, 40 mg/kg) have been studied in forced swim test, tail suspension test, hot plate

Conclusions In this paper a new method for numerical solution of ordi- nary differential equations based on pseudo differential operators and Haar wavelets is proposed.. Its

Mallory tries to to disclose balance AB by routing invalid payments through M ↔ A ↔ B , using the basic BDA algorithm.. The inputs parameters for the algorithm are the target node B

We further defined quantitative trait loci (QTL) that affect the initiation of flowering in each of these species. QTL analyses were performed separately for two different