Basics of load flow study

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: