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LOAD FLOW ANALYSIS - I : SOLUTION OF LOAD FLOW AND RELATED PROBLEMS USING GAUSS-SEIDEL METHOD

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OBJECTIVES

i. To write a computer program to solve the set of non-linear load flow equations using

Gauss-Seidel Load Flow (GSLF) algorithm and present the results in the format

required for system studies.

ii. To investigate the convergence characteristics of GSLF algorithm for normally

loaded small system for different acceleration factors.

iii. To investigate the effects on the load flow results, load bus voltages and line /

transformer loadings, due to the following control actions:

a. Variation of voltage settings of P-V buses

b. Variation of shunt compensation at P-Q buses

c. Variation of tap settings of transformer

d. Generation shifting or rescheduling.

SOFTWARE REQUIRED

GAUSS – SEIDEL METHOD module of AU Powerlab or equivalent

THEORETICAL BACKGROUND

Need For Load Flow Analysis

Load Flow analysis, is the most frequently performed system study by electric utilities. This analysis is performed on a symmetrical steady-state operating condition of a power system under “normal” mode of operation and aims at obtaining bus voltages and line / transformer flows for a given load condition. This information is essential both for long term planning and next day operational planning. In long term planning, load flow analysis, helps in investigating the effectiveness of alternative plans and choosing the “best” plan for system expansion to meet the projected operating state. In operational planning, it helps in choosing the “best” unit commitment plan and generation schedules to run the system efficiently for the next day’s load condition without violating the bus voltage and line flow operating limits.

Description of Load Flow Problem

In the load flow analysis, the system is considered to be operating under steady state balanced condition and per phase analysis is used. With reasonable assumptions and approximations, a power system under this condition may be represented by a power network as shown by the single-line diagram in Annexure 3.1.

The network consists of a number of buses (nodes) representing either generating stations or bulk power substations, switching stations interconnected by means of transmission lines or power transformers. The bus generation and demand are characterized by complex powers flowing into and out of the buses respectively. Each transmission line is characterized by its π equivalent circuit. The transformer with off-nominal tap ratio is characterized by their ‘π’ equivalent circuit. Shunt compensating capacitors or reactors are represented as shunt susceptance.

Load Flow analysis is essentially concerned with the determination of complex bus voltages at all buses, given the network configuration and the bus demands. Let the given system demand (sum of all the bus demands) be met by a specific generation schedule. A generation schedule is nothing but a combination of MW generation (chosen within their ratings) of the various spinning generators the total of which should match the given system demand plus the transmission losses. It should be noted that there are many generation schedules available to match the given system demand and one such schedule is chosen for load flow analysis.