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.
6.
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.
10.
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: