# Computer Aided Power System Design and Analysis

Topics: Electrical engineering, Electric power transmission, Per-unit system Pages: 11 (2377 words) Published: January 22, 2013
NORTHUMBRIA UNIVERSITY
School of Computing, Engineering and Information Sciences

BEng (Hons) Electrical and Electronic Engineering

Computer Aided Power System Design and Analysis

Module: EN0310 Power Systems
Assignment Tutor: Dr G.A. Putrus and Dr.Z.Gao
Assignment: Value: 20% of Module
Student name: FANGFANG LU (w10024301)

Contents
1. Introduction---------------------------------------------------------------------------------------1 2. Construct the Network--------------------------------------------------------------------------2 2.1Construction of the Network Model-------------------------------------------------------2 2.2 Approximations and Assumptions Made-------------------------------------------------3 3. Computer Aided Design------------------------------------------------------------------------4 3.1 Load Flow Analysis-------------------------------------------------------------------------4 3.2 Unbalanced Fault Calculations------------------------------------------------------------5 4. Analysis of Power System---------------------------------------------------------------------7 4.1 Calculation of Short-circuit level at Bus 4 ----------------------------------------------7 4.2 Unbalanced fault Calculations ------------------------------------------------------------9 5. Active and Reactive Power Fl

ow-----------------------------------------------------------13 6. Methods of Voltage and Frequency Control-----------------------------------------------15 7. Conclusions-------------------------------------------------------------------------------------16 8. References--------------------------------------------------------------------------------------17

1. Introduction
Under normal conditions electrical transmission systems operate in their steady-state mode and the basic calculation required to determine the characteristics of this state is termed load flow (or power flow). The solution is expected to provide information of voltage magnitudes and angles, active and reactive power flows in the individual transmission units, losses and the reactive power generated or absorbed at voltage-controlled buses. In the laboratory, we can do the simulation to the complex network in the ERCAS software, and use the analytical procedure to get the data in each network components.

2. Construct the Network
2.1 Construction of the Network Model
Using ERACS software package, the network is drawn as shown in Figure 2.1.

Figure 2.1

Choosing a 100 MVA study case, construct the network given. The system positive, negative and zero sequence reactances (X1,X2 and X0, respectively) are given in p.u. on 100MVA base as follows: G1: X1=0.3, X2=0.2 and X0=0.05

G2: X1=0.2, X2=0.12 and X0=0.03
T1: X1=X2=X0=0.15 T2: X1=X2=X0=0.1
L1 and L2: X1=X2=0.15 and X0=0.3
Notice that the generator G1 id modelled as a slack generator with 1∠00 p.u. voltage. For generator G2, it is assigned active power of 50 MW and reactive power of 40MVAr.

The main object of fault analysis is to calculate fault currents and voltages for the determination of circuit-breaker capacity and protective relay performance. Early methods used in the calculation of fault levels involved the following approximations. * All voltage sources assumed a one per unit magnitude and zero relative phases, which is equivalent to neglecting the prefault load current contribution. * Transmission plant components included only inductive parameters. * Transmission line shunt capacitance and transformer magnetising impedance were ignored. Based on the above assumptions, simple equivalent sequence impedance networks were calculated and these were interconnected according to the fault specification. Conventional circuit analysis was then used to calculate the sequence voltage and currents and with them, by means of the inverse...