1. Introductions
In this assignment, a software package named ‘ERACS’ is used for diagram building of a power system, Load flow analysis, Balanced and Unbalanced Short Circuit analysis.
Calculate the short circuit level (in MVA) in balanced, the current fed into the fault and the voltages of the healthy at bus 4 of the unbalanced circuit.
Analyze and compare these two results which got by theory and analytical procedures with the system performance.

2. Procedures and Comments I. Using ERACS software package to construct the network shown below.
Figure 1.1 example network

The network diagram constructed by ERACS:
Figure 1.2 constructed network
Setting notice:
The system positive, negative and zero sequence …show more content…

* In the software performance, table 2.2 shows the voltage generated by G1 and flows to bus1 is 1.0 pu, but a voltage drop happens during the way to the other parts of the network, so it is not 1.0pu in bus2 also not in the other busbars except bus1. However, in calculation 1.0 pu voltage is default as base voltage pu. * The use of approximate value also need to be taken into account.

III. Unbalanced fault calculations
First, simplify the positive, negative and zero sequence reactances in the network.
Positive Sequence : G
0.3 0.15 0.15 0.15 0.2143 G I1

0.1 0.2 F

Z1=j0.2143 Figure 3.1

Negative Sequence : 0.2 0.15 0.15 0.15

0.1644 I2

0.1 0.12 F F

Z2=j0.1644 Figure 3.2
Zero Sequence :
Considering zero-sequence currents circulate in the delta but no in the lines on the delta side. The reactance diagram is like figure3.3

0.1 0.03

Vaild parts

0.13

I0 Z0 =j0.13 F

Figure 3.3

A. Sigle Phase to Earth Fault
Load the single phase to earth fault study on