Download Distributed Generation at Clemson University

Impact of Distributed Generation on
Fault Induced Transients: A Case Study
Sukumar Brahma
Adly Girgis
Clemson University Electric Power Research Association
Clemson University
Clemson SC 29634
Introduction
• This presentation analyzes following transients in a
distribution system with/without the presence of DG
in an actual 22 bus system:
Transients due to Single Phase Faults
Transients due to Three Phase Faults
• Effect of Grounding of DG is Observed
• Effect of Distance of fault from DG is observed
Modeling
• 22 bus distribution feeder modeled on
PSCAD
• DG is modeled as a synchronous
generator with exciter and governor
• Interconnecting transformer assumed Y
connected on system side
• System loads modeled as constant
power loads
• Lines modeled as coupled PI circuit
Distribution Feeder Considered for Analysis
1550
1549
SUBSTATION
1644
16
16
46
1551
1647
BUS 0
45
1552
16
48
1553
16
4
ALL LINE SECTIONS 3 (ABC)
UNLESS OTHERWISE NOTED.
9
1653
1651 1650
1554
1555
1556
2
165
1668
A
1667
AB
16
66
1569
16
5
6
1560
1
60 658
6
1
1563
16
1558
1657
1570
1571
DG connected to this bus
1559
16
55
61
65
1568
16
1566
1561
1659
1572
1654
1573
1562
DG Capacity 30% of
Feeder Load
Single Phase Fault Without DG
3565 A
25% Increase
Three Phase Fault Without DG
5635 kV
25% Overshoot
Single Phase Fault With DG
188% more than
without DG
25% Increase after
DG is
Disconnected
• Worse in terms of current
• Better in terms of voltage
Three Phase Fault With DG
75% more than without DG
25% Overshoot
Same as without DG
Single Phase Fault With DG Reactance- Grounded
101% more than without DG
Voltage profile worsens
Single Phase Fault Away From DG
Decreases
No Perceptible Change
Three Phase Fault Away From DG
Increases for this case
High frequency transient
more, but overshoot reduces
Conclusion
• Without DG, single phase faults can be more severe in terms of
voltage and three phase faults in terms of current.
• Due to DG, transient fault current peaks increase for both types of
fault.
• Transient voltage rise when fault clears is same with/without DG
• If DG is solidly grounded, voltage rise of healthy phases for
single-phase faults can be less severe, but single-phase currents
can increase drastically.
• If DG is grounded through impedance, single-phase fault currents
would get less severe, but voltage rise of healthy phases can get
worse.
• For single-phase faults away from DG, currents reduce, but the
same cannot be said for three-phase fault currents. There is a
decrease in overshoot when three phase fault is cleared.
• High frequency transients introduced in voltage waveform takes
about the same time to die down with or without DG. The time
taken in the case studied here was around half a cycle.