LOAD FLOWS

General introduction & importance of load flows

Solution of load flow equations

Internet sites: Sparsity Technology

Load flow programs,Voltage stability phenomenon

Objective type questions

Sparsity Technology - for power systems

PFLOW: a "commercial-grade" continuation power flow program, that can be used to research static voltage stability phenomena in detailed AC-HVDC-FACTS power system models. The program is written in C and C++, and two versions for WINDOWS 95 and UNIX are available, including examples and a brief tutorial.

PCFLO and PCFLOH PCFLO is a load flow program which also includes short circuit and harmonics capabilities. PCFLOH is a harmonics-only version of PCFLO, with special user interface for harmonic studies. PCFLO contains some features not found in many load flow programs. For example, it lists the power loss on each line and transformer. It allows the user to control the transition point from Gauss-Seidel to Newton-Raphson. Also, it lists the optimal bus order for selected method 1, 2, or 3 in a
separate output file, which is helpful to students who are learning how to properly order busses. (for Windows 95/98/NT)

PowerWorld™ Simulator: (12 bus version) solves the power flow and economic dispatch problems. It is an interactive power system simulation package designed to simulate high voltage power system operation on a time frame ranging from several minutes to several days. Powerful visualization techniques are used on an interactive basis, resulting in an extremely intuitive and easy to use graphical user interface (GUI). The GUI includes animated one-line diagrams with support for panning, zooming and conditional display of objects. The software runs under Microsoft Windows 95/98/NT.

Matlab Power Flow Program

Internet based full AC power flow, please see at: www.InteractWithPower.com .Free (for testing and educational purposes) full AC power flow version. Only standard internet browser needed. No additional SW installation needed at your own computer. Steps: Click on "Create account ..."; Specify your data including your correct Email (mandatory) address, accept usage conditions, then choose AC power flow (ready for various "standard" IEEE power flow networks (14, 57,118, 300 IEEE bus systems); you can also feed your own IEEE cdf data sets!). A great opportunity for academics (and professionals ?) to share great power applications with the power system community.

Objective type questions

Fig.1 represents a sample power network. The reactances of the lines are marked in the figure, in ohms. The Ybus(2,2) entry is

Ans. a

The real or reactive power balance equations in a power system network consist of

Linear algebraic equations

Non-linear algebraic equations

Linear differential equations

Ans. b

The presence of phase-shifting transformers in a power system will affect its load flow solution in the following way

Only the diagonal elements of Ybus will change

Ybus will not be symmetrical

Load flow solution cannot be obtained.

General introduction & importance of load flows

Concept of power balance at each node in the power network. Real & reactive power flows. State vector and utility of the information contained in the state vector for various studies (such as planning & operation) in the power system.

Buses, injected power at each bus, real & reactive power balance equations. Properties & formulation of Ybus. Formulation of Ybus by observation. The impedance matrix.

Classification of buses. Specification of variables at different buses. Definition & need of slack bus. Physical interpretation of the power flow equations. The nature of power flow equations.

Solution of load flow equations

Emphasise the difficulty in obtaining a closed form solution of the power flow equations. The need for iterative solution methods. Gauss iterative method. Steps in the iterative solution. Convergence criterion. Acceleration factors.

Gauss-Seidel method of solution. Steps in the iterative solution. Introduction to the Newton -Raphson method.