26-04-2014, 03:54 PM
Power Flow Analysis
Power Flow .ppt (Size: 212.5 KB / Downloads: 10)
The Power Flow Problem
Power flow analysis is fundamental to the study of power systems.
In fact, power flow forms the core of power system analysis.
power flow study plays a key role in the planning of additions or expansions to transmission and generation facilities.
A power flow solution is often the starting point for many other types of power system analyses.
In addition, power flow analysis is at the heart of contingency analysis and the implementation of real-time monitoring systems.
Problem Statement
For a given power network, with known complex power loads and some set of specifications or restrictions on power generations and voltages, solve for any unknown bus voltages and unspecified generation and finally for the complex power flow in the network components.
Power Flow Study Steps
Determine element values for passive network components.
Determine locations and values of all complex power loads.
Determine generation specifications and constraints.
Develop a mathematical model describing power flow in the network.
Solve for the voltage profile of the network.
Solve for the power flows and losses in the network.
Check for constraint violations.
Formulation of the Bus Admittance Matrix
The first step in developing the mathematical model describing the power flow in the network is the formulation of the bus admittance matrix.
The bus admittance matrix is an n*n matrix (where n is the number of buses in the system) constructed from the admittances of the equivalent circuit elements of the segments making up the power system.
Most system segments are represented by a combination of shunt elements (connected between a bus and the reference node) and series elements (connected between two system buses).
Difficulties
Unless the generation equals the load at every bus, the complex power outputs of the generators cannot be arbitrarily selected.
In fact, the complex power output of at least one of the generators must be calculated last, since it must take up the unknown “slack” due to the uncalculated network losses.
Further, losses cannot be calculated until the voltages are known.
Also, it is not possible to solve these equations for the absolute phase angles of the phasor voltages. This simply means that the problem can only be solved to some arbitrary phase angle reference.
Guess Solution
It is important to have a good approximation to the load-flow solution, which is then used as a starting estimate (or initial guess) in the iterative procedure.
A fairly simple process can be used to evaluate a good approximation to the unknown voltages and phase angles.
The process is implemented in two stages: the first calculates the approximate angles, and the second calculates the approximate voltage magnitudes.
Power Flow .ppt (Size: 212.5 KB / Downloads: 10)
The Power Flow Problem
Power flow analysis is fundamental to the study of power systems.
In fact, power flow forms the core of power system analysis.
power flow study plays a key role in the planning of additions or expansions to transmission and generation facilities.
A power flow solution is often the starting point for many other types of power system analyses.
In addition, power flow analysis is at the heart of contingency analysis and the implementation of real-time monitoring systems.
Problem Statement
For a given power network, with known complex power loads and some set of specifications or restrictions on power generations and voltages, solve for any unknown bus voltages and unspecified generation and finally for the complex power flow in the network components.
Power Flow Study Steps
Determine element values for passive network components.
Determine locations and values of all complex power loads.
Determine generation specifications and constraints.
Develop a mathematical model describing power flow in the network.
Solve for the voltage profile of the network.
Solve for the power flows and losses in the network.
Check for constraint violations.
Formulation of the Bus Admittance Matrix
The first step in developing the mathematical model describing the power flow in the network is the formulation of the bus admittance matrix.
The bus admittance matrix is an n*n matrix (where n is the number of buses in the system) constructed from the admittances of the equivalent circuit elements of the segments making up the power system.
Most system segments are represented by a combination of shunt elements (connected between a bus and the reference node) and series elements (connected between two system buses).
Difficulties
Unless the generation equals the load at every bus, the complex power outputs of the generators cannot be arbitrarily selected.
In fact, the complex power output of at least one of the generators must be calculated last, since it must take up the unknown “slack” due to the uncalculated network losses.
Further, losses cannot be calculated until the voltages are known.
Also, it is not possible to solve these equations for the absolute phase angles of the phasor voltages. This simply means that the problem can only be solved to some arbitrary phase angle reference.
Guess Solution
It is important to have a good approximation to the load-flow solution, which is then used as a starting estimate (or initial guess) in the iterative procedure.
A fairly simple process can be used to evaluate a good approximation to the unknown voltages and phase angles.
The process is implemented in two stages: the first calculates the approximate angles, and the second calculates the approximate voltage magnitudes.