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1. Presented By:
Arshdeep Kaur
Department of Electrical Engineering
GNDEC ,Ludhiana

2. What is a Load Flow Study???
It is a steady-state analysis whose target is to determine
the
 Voltages
 Currents
 Real and Reactive power flows in a system under a
given load conditions

3.  A load flow study is done on a power system to ensure that
 Generation supplies the demand (load) plus losses.
 Bus voltage magnitudes remain close to rated values
 Generation operates within specified real and reactive
power limits
 Transmission lines and transformers are not overloaded.

4. A Load Flow Study Specifically Investigates the
Following
 Bus bar voltages
 Effect of rearranging circuits and incorporating new
circuits on system loading.
 Effect of injecting in-phase and quadrature boost
voltages on system loading.
 Optimum system running conditions and load
distribution.
 Optimum system losses.
 Optimum rating and tap range of transformers.

5. The basic equation for power-flow analysis is derived from the nodal
analysis equations for the power system.
For example, for a 4-bus system
where Yij are the elements of the bus admittance matrix,
Vi are the bus voltages
Ii are the currents injected at each node.
•The node equation at bus i can be written as

6.  Relationship between per-unit real and reactive power supplied
to the system at bus i and the per-unit current injected into the
system at that bus:
where Vi is the per-unit voltage at the bus;
Ii* - complex conjugate of the per-unit current injected at the bus;
Pi and Qi are per-unit real and reactive powers.
Therefore,

7. Power-flow Analysis Equations

8.  The starting point of a load flow problem is a single line
diagram of the power system, from which input data for
computer solutions can be obtained. Input data consist of bus
data, transmission line data and transformer data.
 A bus is a node at which one or many lines, one or many loads
and generators are connected.

9. Formulation of load-flow study
In a power system each node or bus is associated with 4
quantities, such as
1. Magnitude of voltage V
2. Phage angle of voltage δ
3. Active power P
4. Reactive power Q
In load flow problem two out of these 4 quantities are specified
and remaining 2 are required to be determined through the
solution of equation.

10. Classification Of
Buses
Slack Bus/Swing
Bus Load Bus/PQ Bus Generator Bus/PV
Bus
Depending on the quantities that have been specified, the
buses are classified into 3 categories.
Bus Classification

11. Each bus is categorized into one of the following bus types:
1. Swing bus / slack bus
Bus Defined To Defined Application
Slack bus V and δ
usually
V1= 1 d1 =0o
P and Q There is only one
bus of this type in
given power system
This is numbered as
one for convenience

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