1. 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

2. 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 Introduction

3. 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 Modeling

4. Distribution Feeder Considered for Analysis DG connected to this bus DG Capacity 30% of Feeder Load

5. Single Phase Fault Without DG 25% Increase 3565 A

6. Three Phase Fault Without DG 25% Overshoot 5635 kV

7. 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

8. Three Phase Fault With DG 75% more than without DG25% Overshoot Same as without DG

9. 101% more than without DG Voltage profile worsens Single Phase Fault With DG Reactance- Grounded

10. Single Phase Fault Away From DG Decreases No Perceptible Change

11. Three Phase Fault Away From DG Increases for this case High frequency transient more, but overshoot reduces

12. 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. Conclusion