Analysis of Power Flow, Continuous Power Flow and Transient Stability of IEEE-14 Bus Integrated

Wind Farm Using PSATSatish Kumar,Ph.D.Scholar Department of Electrical Engineering NIT, Kurukshetra, Haryana, India

Ashwani Kumar, Professor Department of Electrical Engineering, NIT, Kurukshetra, Haryana, India ashwa_ks@yahoo.co.in

N K Sharma, Director Vidya college of Engineering Meerut, U.P., India drnikhlesh@gmail.com

Abstract—Renewable energy systems are becoming necessary for higher power demands to compensate for maximum demand by the consumer. Wind energy system is one of the methods to generate power in connection with the conventional power systems. But when this wind farm is integrated to the grid system, the stability of the system tends to decrease.In this paper IEEE-14 Bus system using PSAT is used to evaluate the performance of the system, integrated with wind energy system, when subjected to fault. Using PSAT we first build an IEEE-14 bus test system and analyzed the performance by simulation. We introduced a three-phase symmetrical fault at various buses and study the voltage variations in all the buses with respect to time. We have connected a wind turbine at different buses and study the effect of wind power on the transient fault behavior. Our results show that the integration of wind farm has increased the transit stability of the system.

Keywords—Voltage Stability,Voltage Instability, Transient Stability, Wind Turbine, PF,CPF

I. INTRODUCTION Power system stability has been a major concern in the

area of power system because of voltage collapse. Stability analysis is important for designing the power network & for power enhancement.so various power networks are analyzed to operate in stable region. Due to increase in power demand day by day more & more focus is being done to control the voltage profile of the system. With increase in power demand new resource of power generation is being done .wind energy is one of the renewable sources of energy which is in demand now a day, because of various advantages associated with it. When this wind farm is integrated to the conventional grid, the voltage profile of system tends to decrease .this causes voltage instability. This voltage instability is due to the decrease in the reactive power of the lines.

II. VOLTAGE STABILITY The purpose of Voltage stability analysis is to keep the power system with in the stability limits. Voltage instability includes generation, transmission and distribution. A system is said to be unstable when there is a progressive or

uncontrolled drop in voltage magnitude after a disturbance, increase in load demand or change in operating conditions [1]. Many major blackouts caused by power system instability have been studied so far, which illustrates the importance of these phenomena [2].Various types of voltage stabilities, their classification & transient stability have been studied to make voltage instability problem more confined & conceptual [3].

III. TRANSIENT STABILITY For stability analysis, problems are generally divided into two major categories

• Steady-state stability • Transient stability

The ability of the power system to regain synchronism after small and slow disturbances is called Steady-state stability .An extension of the steady-state stability is known as the dynamic stability. Transient stability studies deals with the effects of large, sudden disturbances, such as the occurrence of the fault, the sudden outage of a line.so when symmetrical fault is introduced in the system, transient stability of the system gets disturbed. Hence controlling transient stability is another challenge, especially when system is integrated with some external source. There are some methods to improve the transient stability of the integrated system [4] [5] [6].

IV. WIND FARM TECHNOLOGY Over the past two decades development of renewal energy resources has intensified. Of the various energy resources, wind energy being freely available and non-polluting, has been favored by number of users now a days as it is economically competitive with the conventional sources. from the past decade Wind power has grown annually at the rate of 20%.this growth rate is faster than any another renewal energy resource in the world. This has become possible only due to the availability of the wind power, low cost & highly reliable. It is expected that throughout the world almost 12% of the world’s electricity will be generated from wind power by 2020 [7].

978-1-4673-7492-7/15/$31.00 ©2015 IEEE

V. PSAT(POWER SYSTEM ANALYSIS TOOLBOX) PSAT is a MATLAB toolbox for electric power system analysis and control. The command line version of PSAT is also GNU Octave compatible. PSAT includes power flow, continuation power flow, optimal power flow, small signal stability analysis and time domain simulation. All operations can be assessed by means of graphical user interfaces (GUIs) and a Simulink-based library provides an user friendly tool for network design [8].PSAT core is the power flow routine, which also takes care of state variable initialization. Once the power flow has been solved, further static and/or dynamic analysis can be performed. These routines are

• Optimal power flow(OPF) • Continuation Power flow(CPF) • Small signal stability analysis • Time domain simulations

PSAT also includes a variety of utilities, as follows, • Simulink library for drawing networks • GUIs for settings system and routine parameters • User defined model construction and installation • GUI for plotting results • Filters for converting data to and from other

formats • Command logs

VI. TIME DOMAIN SIMULATION Time domain simulation is done in order to find out satisfactory performance of any system subjected to various changes in the system like, integration with some renewal resources, introduction of some faults in the system. When fault/disturbances in the system is introduces its, clearance with critical clearing time is calculated. Least critical clearing time is an indication of resuming stability in a very short span of time.

1. Power Flow(PF) A power flow study (load-flow study) is a steady-state analysis whose aim is to determine the voltages, currents, and real and reactive power flows in a system under a given load conditions. The purpose of power flow studies is to plan ahead and account for various hypothetical situations. For example, if a transmission line is be taken off line for maintenance, can the remaining lines in the system handle the required loads without exceeding their rated values.

2. Contineous Power Flow(CPF) Continuous power flow method is used to determine the voltage collapse point in the system. In this paper CPF using PSAT is performed for integrated wing farm and once the fault is introduced within the system Continuation power flow allows the load voltage to be computed even when the power flow Jacobean matrix is singular. The complete PV curve, including the nose point and the lower part of the curve, can be drawn using continuation power flow.

VIII. POWER FLOW AND CONTINUOUS POWER FLOW FOR IEEE-14 BUS SYSTEM BASE CASE

We have taken IEEE 14-bus model as the base model for stability analysis. Now using PSAT we perform power flow, continuation power flow, and time domain analysis for IEEE-1 bus test system

TABLE I. Power Flows results for IEEE-14 Bus Test System

TABLE II. Continuous Power Flows results for

IEEE-14 Bus Test System

Network Statistics Number Solution Statistics Number Buses 14 Number of Iterations 41 Lines 16 Maximum P mismatch 0 Transformers 4 Maximum Q mismatch 0 Generators 9

Power rate [MVA] 100 Load 11

Network Statistics Number Solution Statistics Number Buses 14 Number of Iterations 3

Lines 16 Maximum P mismatch 0

Transformers 4 Maximum Q mismatch 0

Generators 5 Power rate [MVA] 100

Loads 11

Fig.1 IEEE-14 Bus Test System

Fig.2 Voltage Profile of all buses for base case using PF

Fig.3 Angle Profile of all buses for base case using PF

Fig.4 Reactive Power Profile of all buses for base case

using PF

Fig.5 Real power profile of all buses for base case using PF

Fig.6 Voltage Profile of all buses for base case using CPF

Fig.7 Angle Profile of all buses for base case using CPF

Fig.8 Reactive Power Profile of all buses for base case

using CPF

Fig.9 Real Power Profile of all buses for base case using

CPF

Fig.10 Omega v/s time graph for IEEE-14 Bus system Base

Case

TABLE III. Global Summary Report CPF for IEEE-14

Bus Test System (Base Case)

TABLE IV. Power Flows results for IEEE-14 Bus Test

System (with fault)

TABLE V. Continuous Power Flows results for IEEE-

14 Bus Test System (with fault)

Power Total Generation Total Load Total

LossesReal Power [p.u.] 7.6104 7.6104 1.4672 Reactive Power [p.u.] 7.6553 7.6553 5.7246

Network Statistics Number Solution Statistics Number Buses 14 Number of Iterations 41 Lines 16 Maximum P mismatch 0 Transformers 4 Maximum Q mismatch 0 Generators 9

Power rate [MVA] 100 Load 11

Network Statistics Number Solution Statistics Number Buses 14 Number of Iterations 3

Lines 16 Maximum P mismatch 0

Transformers 4 Maximum Q mismatch 0

Generators 5 Power rate [MVA] 100

Loads 11

Fig.11 IEEE-14 Bus system with fault at Bus No-2

Fig.12 Voltage Profile of all buses using PF, when fault is

introduced

Fig.14 Reactive power Profile of all buses using PF, when

fault is introduced

Fig.13 Angle Profile of all buses using PF, when fault is

introduce

Fig.15 Real power Profile of all buses using PF, when fault is introduced

TABLE VI. Global Summary Report CPF for IEEE-14

Bus Test System (Base Case)

Power Total Generation Total Load Total

LossesReal Power [p.u.] 7.6104 6.1432 1.4672 Reactive Power [p.u.] 7.6553 1.9307 5.7246

Fig.16 Voltage Profile of all buses using CPF, when fault is introduced

Fig.17 Angle Profile of all buses using C PF, when fault is introduced

Fig.18 Reactive power Profile of all buses using CPF, when fault is

introduced

Fig.19 Real power Profile of all buses using CPF, when fault

is introduced

Fig.20 Omega v/s time graph for IEEE-14 Bus system subjected to

fault

Fig.21 IEEE-14 Bus system with wind turbine at Bus No-14

VIII. RESULT AND DISCUSSION

In this paper IEEE-14 bus sytem is used to see the effect on transient behaviour of the system when subjected to fault and when wind turbine is integrated at different locations of the said system.In the first case power flow, continuous power flow and time domain simulation of the system is studied using PSAT. Various voltage profile, angle profile of Buses, reactive power & real power of different buses have been

shown in Fig.2 to Fig.19.In the next step we have introduced the fault and analysed power flow, continuous power flow & time domain analysis. Time domain simulation in figure.20 shows that the system is under unstable region.In order to improve the transient behaviour of the system one wind turbine generator is connected to system through a transmission line at Bus No-14. Fig.22 shows that the time domain behaviourof the system is slightly improved when we introduced wind turbine at bus-14.Further we have connected the same system at Bus No-1. We can see from Fig. 23 that the time response of the system is greatly enhanced when we introduced wind turbine at Bus No -1. Hence based on the above results and discussions it is seen that transient behavior of the system depends on the location of wind turbine as well.It can also be concluded that the large amount of wind power penetration causes instability in the power system & it happens when a very large part of the synchronous generation capacity is replaced by wind power.

References

[1] P. Kundur,“Power System Stability And Control,” McGraw-Hill Inc.,New York,USA,1994

[2] G.S. Vassell, “Northeast Blachout of 1965,” IEEE Power Engineering Review,pp 4-8,jan. 1991,

[3] P. Kundur, John Pesreba “Definition & Classification Of Power System Stability,” IEEE transactions of power system, Vol-19,No-2,May-2004.

[4] Tang Fan, Liu Tian-qi,LI Xing-yuan,“Improving Transient Stability of Wind Farm Consisting of Fixed Speed Induction Generator by Series Connected Dynamic Braking Resistors,”Power System Technology 2010 34(4).

[5] Wang Xiangzhong,Wu Xiaojie,Chai Jianyun.“Characteristic analysis of wind induction generator with RCC,”.Acta Energiae Solaris Sinica 2005 26(4),pp 447-451(in Chinese).

[6] Lin Li,Sun Caixin,Wang Yongping,etal. “Calculation analysis and control strategy for voltage stability of power grid with large capacity wind farm interconnected,”.Power System Technology,2008,32(3).

[7] Dao Trung Hieu, V.K. Ramachandaramurthy, Min Min Kyaw, “Voltage Stability of Wind Farms Connected to Transmission Network Using VSC-HVDC”.PEA-AIT international conference on sustainable development:issue and strategies(ESD 2010),Thailand,2-4 June 2010.

[8] F. Milano, “An Open Source Power System Analysis Toolbox,” IEEE Transactions On Power Systems vol. 20,No.3, August 2005.

Fig.22 Omega v/s time graph for IEEE-14 Bus system integrated

with wind turbine connected at Bus No-14

Fig.23 Omega v/s time graph for IEEE-14 Bus system integrated with wind turbine connected at Bus No-14