chapter 3 - Bentham Science

Fault Analysis in Power Systems Applications of Spreadsheets in Education The Amazing Power of a Simple Tool 5
4. Transmission lines are represented by their equivalent series reactances. Series resistances
and shunt admittances are ignored.
5. Synchronous machines are represented by constant-voltage sources behind subtransient reactances.
Armature resistance, pole saliency, and saturation effects are ignored.
To illustrate the analysis of symmetrical faults, consider the five-bus power system whose oneline
diagram is shown in Fig. (1.1). Machine, transformer, and line data are given in Table 1.1. The
data are given in per unit (p.u.) of a common base.
Eg1
Generator 1 Transformer 1
jX" d 1
jXT1 j 0.04 j 0.025
1
jX25
j 0.1
jX45
j 0.05
5 4
2
Transmission lines
j 0.125
jX24
Transformer 2 Generator 2
jXT2 jX" d 2
j 0.02
Fig. (1.1): One-line diagram of power system for symmetrical fault analysis.
Table 1.1: Synchronous machine, transformer, and transmission line data
Generator
Bus Subtransient reactance, X ′′
d (p.u.)
1 0.04
3 0.02
Transformer
Bus-to-Bus Leakage reactance, XT (p.u.)
1–5 0.025
3–4 0.02
Line
Bus-to-Bus Series reactance, XL (p.u.)
2–4 0.125
2–5 0.1
4–5 0.05
It is also assumed that the pre-fault voltage at the faulted bus is VF = 1.05e j0o p.u. Since
machine subtransient reactances are used in the analysis, the currents to be calculated are then
subtransient fault currents. The purpose of the analysis is to determine the subtransient fault currents
and phase voltages in each bus when a three-phase short circuit occurs at bus 1. The calculations
are then repeated for three-phase short circuits occurring at bus 2, 3, and so on.
3
j 0.02
Eg2