Ybus formation for load flow studies

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ABSTRACT Ø Load flow is an important power system analysis component to ensure the system upgrades, future upgrades and present pr esent distribution equipment meeting the present and future requirements.

Ø Load flow study in power p ower system is the steady state solution of power system network.

Ø The information obtained from load flow solution is used for the continuous monitoring of current state of the system and for analyzing the











INTRODUCTION  Load flow studies can be used to obtain the voltage magnitudes and angles ang les at each bus in the steady state.  Once the bus voltage magnitudes and their angles are computed using the load flow, flow, the real and reactive power flow f low through each line can be computed.

 This project deals with Ybus formation using different methods for load flow analysis.

 Formation of Ybus plays a vital role in solving any load flow problem.  Ybus matrix is

matrix that is why it is preferred over Z matrix











CLAS CLASSI SIFI FICA CATI TION ON OF BUSE BUSES S Load Buses: In these buses no generators are connected and hence the generated real power P P Gi and reactive power Q power QGi are taken as zero.

Voltage Controlled Buses: These are the buses where generators are connected.

slack or swing buses : Usually this bus is numbered 1 for the load flow studies. This bus sets the angular reference for all the other o ther buses.











GAUS GAUSS S SEID SEIDEL EL METH METHOD OD ALGORITHM FOR LOAD-FLOW SOLUTION

 

With the load profile known at each bus (i.e. PDi and QDi known), allocate PGi and QGi to all generating stations Assembly of bus admittance matrix Y BUS Iterative computation of bus voltages Current at the ith bus *= I Pi-jQ / V i i i = ∑nk 1 Yik Vk











Comp Comput utat atio ion n of slac slack k bus bus powe power r Si*=Pi-jQi Comp Comput utat atio ion n of line line flow flows s

The current rent fed by bus bus i into into the line can can be express resse ed as Iik =Iik1 +Iik0 =(Vi-Vk)Yik +ViYik0 Th

f d i t

th

li

f

b

i i













Consider a set of n non-linear algebraic equations 

f i (x1, x2,……, xn) =0;

i=1,2,3, ….., n



f i (x10 +∆x10, x20 +∆x20,… …….. xn0+∆xn0) = 0;











Or in vector matrix form f 0+J 0 ∆x0=0 J0 is known as the jacobian matrix the above Eq can be written as f 0≈ [-j0 ] ∆x0











f ip =Pi (specified)-Pi(calculated)=∆Pi











Bus type

Number of buses

Qualities specified

Number of Number of δ i available |Vi| state variables equations

Slack i=1

1

δi , |Vi|

0

0











DECOU ECOUP PLED LED LOA LOAD FLOW LOW METHO ETHOD D 



The decoupled power flow method is an approximate version of Newton-Raphson procedure. The approximation of the Newton-Raphson

























The line susceptances

are many times larger than the























































































































































A=  1  1  0  0  0 

-1 0 0 0 0



A=  1  1  0 

-1 0 0

0 -1 0











A=  1  1  0  0  0 

-1 0 1 0 0

0 -1 0 0 0

-1 0 1

0 -1 -1



A=  1  1  0 











A=  1  1  0  0  0 

-1 0 1 1 0

0 -1 -1 0 0

-1 0 1

0 -1 -1



A=  1  1  0 

0 0 0











A=  1  1  0  0  0 

-1 0 1 1 0

0 -1 -1 0 1

0 0 0 -1 0

-1 0 1

0 -1 -1

0 0 0



A=  1  1  0 











 YBUS =  

3.0000 - 9.0000i -2.0000 + 6.0000i -1.0000 + 3.0000i

-2.0000 + 6.0000i 3.6667 -11.0000i -0.6667 + 2.0000i -1.0000 + 3.0000i  -1.0000 + 3.0000i -0.6667 + 2.0000i 3.6667 -11.0000i -2.0000 + 6.0000i 

0













CONCLUSION Load flow study comprises the magnitude and phase angle of load bus voltages, reactive power at generator buses, the real and reactive power flow on transmission lines, and other variable being specified. 











REFERENCES BOOKS:  Stagg,G.W and A.H.El-Abiad, A.H.El-Abiad, Computer Method in Power System analysis  Nargrath, I.J.and D.P.Kothari, D.P.Kothari, Power System Engineering  Weedy,B.M. and B.J.Cory, Electrical power Systems, 4th Ed., John Wiley, NEW



YORK,1998





















Ybus formation for load flow studies

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