The document presents an overview of a load flow study in power systems, focusing on determining voltages, currents, and power flows under specific load conditions. It discusses the importance of such studies for ensuring generation meets demand, maintaining bus voltage levels, and preventing overloads in transmission lines. Additionally, it outlines the basic equations and classifications of buses involved in the study.

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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