faraday.ee.emu.edu.trfaraday.ee.emu.edu.tr/eeng457/unsymmetrical faults.pdffault analysis • fault...
TRANSCRIPT
2
3
4
5
6
7
8
9
10
Zabc
11
12
13
Key point: generators only produce positive sequence voltages ; therefore only the positive sequence has a voltage source. 14
15
� The positive and negative sequence diagrams for transformers are similar to those for transmission lines.
� The zero sequence network depends upon both how the transformer is grounded and its type of connection. The easiest to understand is a double grounded wye-wye
16
17
� The first step in the analysis of unbalanced faults is to assemble the three sequence networks.
� To do further analysis we first need to calculate the thevenin equivalents as seen from the fault location.
18
With a SLG fault only one phase has non-zero fault current we’ll assume it is phase a.
19
With the sequence networks in series we can solve for the fault currents
20
Example : In the following power system the value of fault impedance is j0.03 pu. Generators are running at no-load at rated voltage and in phase. All network data is expressed on a 100 MVA base. Find the fault current for SLG.
21
Positive Sequence Network
22
Negative Sequence Network
23
Zero Sequence Network
24
25