1. Load Flow Studies Eng. Edvan Moyo BEng, MEng, MBA www.kgrtc.org.zm

2. Expectations

3. Objective
Partcipants should be able to understand and appreciate the importance of load flow studies and the practical application of the studies.

4. Learning Outcomes
At the end of the presentation, participants will be able to:
Understand the purpose of load flow studies
Know the equations used in load flow studies
Know the practical application of load flow studies
Carry out a basic load flow simulation

5. Content Introduction Power Flow Useful Information
The Load Flow Equation
Number of Variables-Number of Equations
Power Flow Specifications: An Example
Practical Application and Simulations

6. Introduction Load flow studies are also known as power flow studies
Most common and important tool in power system analysis
Why carry out power flows?
Used for:
-operation of power systems
-controlling of power systems
-planning for future expansions
-performance of the system

7. Introduction
It allows the engineer to investigate the performance of the network under a variety of outage conditions
Numerical computation are performed by means of an iterative methods; some of the commonly used methods are:
-The Gauss-Seidel Method
-The Newton-Raphson Method
-The Fast Decoupled Load Flow

8. Power Flow Useful Information
A load flow analysis allows identification of:
-real and reactive power flow
-network losses: too high?
-Voltages: too high or too low?
-current flow
-Power factor
-Overload on lines?
In the network with arbitrary number of buses and branches, and with arbitrary topology

9. Commercially Available Software
Generation and Transmission System Simulations
PSS/E
Etap
DigSilent
Matlab Based
PSAT – open source
Matpower
Electricity Market Simulations
AMES – open source
Powerworld
Distribution Systems Simulation
DigSilent
Etap

10. The Load Flow Equations
Load Flow calculations can be made by using:
-Bus admittance matrix(BAM) or
-Bus Impedance matrix(BIM)
However, it is simpler to use BAM approach to the solution of load flow problems.
Bus: is a node at which one or many lines, or where one or more loads and generators are connected

11. Power flow eq.: Current is replaced by P/Q

12. Load Flow Eq. Are non linear
In complex form:
Real Variables, Active (P) and Reactive (Q) Power

13. Number of Variables-Number of Equations.

14. Number of variables-number of equations
n buses
2n real equations
4n variables: 4(P, Q, V, )
2n variables specified(must be known)
2n variables to be calculated from equations

15. Number of variables-number of equations
At each busbar: 2 variables are specified
2 out of 4 variables are not specified at each busbar.
There are 6 possible combinations:
P-V
P-
P-Q
Q-V
Q-
V-
Practical combinationa are 1, 3, and 6

16. Number of variables-number of equations
The following are the three special bus types for load flow studies:
Bus Type
Specified quantities
Unknown quantities
Approximate number
Load Bus or P-Q bus
P, Q
V, 
85%
Generator bus or voltage controlled bus or P-V bus
P, V
Q, 
15%
Reference bus or slack bus or swing bus
V=1, =0 1%

17. Power Flow Specifications: An Example

18. Results (Specifications Unchanged)

19. Practical Application and Simulations
Short circuit studies
Grid integration impact studies
Protection coordination and relay setting verification
Reliability studies
System security and transient stability studies

20. Thank You