Load flow studies analyze the steady state operation of a power system by determining voltage magnitudes and angles, as well as active and reactive power flows. The key purposes of load flow analysis include designing, planning, and optimizing the operation of a power system. The analysis models each bus in the system where generators, transmission lines, and loads connect. Buses are classified based on which two of four parameters - voltage magnitude, voltage angle, active power, and reactive power - are specified as inputs. Load flow equations are then solved to calculate the unknown parameters.

1. By – Mr. A. L. Jamadar

2.  Load flow studies or Power flow studies is the
analysis
 of a power system in normal steady state
condition.
 Load flow studies basically comprises of the
determination of
◦ Voltage
◦ Current
◦ Active Power
◦ Reactive Power

3.  Generation supplies demand(Load) plus
losses.
 Bus voltage magnitude remain close to rated
value.
 Generation operates within specified real and
reactive power limits.
 Transmission line and transformer are not
overloaded.

4.  Designing a power system.
 Planning a power system.
 Expansion of power system.
 Providing guide lines for optimum operation
of power
 system.
 Providing guide lines for various power
system studies.

5.  A bus is a node at which many Transmission lines,
Loads
 Generators are connected.
 It is not necessary that all of them be connected to
every
 bus.
 Bus is indicated by vertical line at which no. of
 components are connected.
 In load flow study two out of four quantities
specified
 and other two quantities are to be determined by
load
 flow equation.
 Depending upon that bus are classified.

7.  A buss at which the Active power and reactive
power
 are specified.
 Magnitude(V) and phase angle(δ) of the
voltage will
 be calculated.
 This type of busses are most common,
comprising
 almost 80% of all the busses in given power
system.

8.  A bus at which the magnitude(V) of the
voltage and
 active power(P) is defined.
 Reactive power(Q) and Phase angle(δ) are to
be
 determined through load flow equation.
 It is also known as P-V bus.
 This bus is always connected to generator.
 This type of bus is comprises about 10% of
all the
 buses in power system.

9.  Voltage magnitude(V) and voltage phase angle(δ)
are
 specified and real(P) and reactive(Q) power are to
be
 obtained.
 Normally there is only one bus of this type is
given in
 power system.
 One generator bus is selected as the reference
bus.
 In slack bus voltage angle and magnitude is
normally
 considered 1+j0 p.u.

11.  The following variables are associated with
each bus:
 Magnitude of voltage(V)
 Phase angle of voltage(δ)
 Active power(P)
 Reactive power(Q)
 The load flow problem can solved with the
help of
 load flow equation(Static load flow equation).

12.  The bus admittance matrix is given by:
 In general the equation for bus-1 can be
written as:
Y11V1+Y12V2+Y13V3=I1
 For bus-2 and bus-3 we can write:
 Y21V1+Y22V2+Y23 V3=I2
 Y31V1+Y32V2+Y33 V3=I3

13.  So Ii=Σ Yik Vk where i,k=1,2,…,n
So complex power is denoted as

14.  In polar form we can write
 The equation is written as:
 Real and reactive power expressed as: