Load Flow Studie

7/29/2019 Load Flow Studie

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Load / Power flow studies


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Load-flow studies are performed to determine

the steady-state operation of an electric power

system. It calculates the voltage drop on each

feeder, the voltage at each bus, and the powerflow in all branch and feeder circuits.

To Determine if system voltages remain within

specified limits under various contingencyconditions, and whether equipment such as

transformers and conductors are overloaded.

Classical methods:

Gauss-Seidel method

Newton Raphson method

Fast Decoupled method


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Variables to be determined for each busFor bus p various parameters are calculated as


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Computational procedure for different bus types:

Slack bus/ Reference bus:

for this bus both |V| and are known and P and Q areunknown.

Computation of slack bus power:

the injected power at Slack bus is computed using

Where s- slack bus


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Load bus / PQ bus:

for this bus both P and Q are known, |V| and areunknown.

Computation of voltage magnitude and phase angle:

voltage magnitude and phase angle computed using


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Generator bus / PV bus / Voltage controlled bus:

for this bus both P and |V| are known, Q and areunknown.

Computation of Reactive power and voltage phase angle:


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Computation of line flows:

Computation of power flow on each transmissionline of network is the last step in power flow

analysis.

Consider the equivalent -model of the line

connecting the two buses p and q as

Bus p Bus q

YpqIqpIpq


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Algorithm / Procedure for obtaining load flow solution

using Gauss-seidel method:

Step:1Read the given data i.e number of buses n,

line admittances Yjk, slack bus voltage, load bus Ppand Qp,

generator bus Pp,|Vp|spec, Qpmin,Qpmax.

Step:2Form YBUS matrix by direct inspection method i.e

Yjk for j=1,2,.n and k=1,2,.n.

Step:3Assume a suitable value called convergence

criterion, here is the specified change in bus voltage i.e

used to compare | |.


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Step:4Set iteration count K=0 and assume voltage

profile of buses as (1+j0) p.u and denoted as

V10

,V20

,V30

,Vn0

except for slack bus.

Step:7Check for generator bus, if it is a generator bus

go to next Step otherwise go to Step :10

Step:5

Set bus count p=1

Step:6

Check for slack bus, if it is a slack bus then

go to Step:13 otherwise go to next Step.


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Step:10For load bus is calculated by using


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Step:13

Repeat Steps 6 to 13 until all the bus voltages have been

computed

Step:15

Calculate slack bus power and line flows using bus voltages.

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Load Flow Studie