Zbus fault analysis example
Define units:
Present this in terms of a series of examples. Use the system below (from the midterm exam).
System Description:
Set bases:
Use the line voltage as the reference
Change of Base Calculations:
Generator 1:
Transformer 1:
Transmisson Line:
Transformer 2:
Generator 2:
Positive Sequence Network (unreduced):
Calculate reduced equivalent for each fault location
Parallel impedance branches: general equation as a function of location on line 1:
Fault at Bus 2:
Fault at Bus 3:
Fault at Bus M (midpoint of line):
Negative Sequence Network (unreduced):
Calculate reduced equivalent for each fault location
Parallel impedance branches: general equation as a function of location on line 1
Fault at Bus 2:
Fault at Bus 3:
Fault at Bus M (midpoint of line):
Zero Sequence Network (unreduced):
Calculate reduced equivalent for each fault location
Parallel impedance branches: general equation as a function of location on line 1
Fault at Bus 2:
Fault at Bus 3:
Fault at Bus M (midpoint of line):
Create Ybus Matrices for Positive, Negative and Zero Sequences
Note that Z_1 is no longer a sparse matrix.....
Negative sequence:
The zero sequence matrix will be different, since there are more open connections
and shorts to ground.
So for a SLG fault at bus 2, with prefault voltage of 1.0pu:
For comparison, if we had done the normal circuit reduction for this fault point we would have:
And for a SLG fault at bus 3, with prefault voltage of 1.0pu:
For comparison, if we had done the normal circuit reduction for this fault point we would have:
So we're consistent
SLG current for a fault at bus 2: