DISTRIBUTED GENERATION ISLANDING - IMPLICATIONS ON POWER SYSTEM DYNAMIC PERFORMANCE Sandhya P Prabhu April 19, 2006

What is islanding ? What is islanding ? Figure 1 Typical distributed system with DG’s [2]

Implications of unintentional islanding Hazard to utility line workers and publicHazard to utility line workers and public Damage to customer equipment if the voltage and frequency provided by the DG is not regulatedDamage to customer equipment if the voltage and frequency provided by the DG is not regulated Damage to the DG’s in the island when island is reconnected to the gridDamage to the DG’s in the island when island is reconnected to the grid

Out - Phase – Reclosing Out - Phase – Reclosing What is reclosing / out – of – phase reclosing?What is reclosing / out – of – phase reclosing? Produces transients which are potentially damaging to utility & customer equipmentsProduces transients which are potentially damaging to utility & customer equipments Figure 2 Phase voltages on source and DG side for a simulation of 180º out-of-phase reclosing [1] Unusually high inrush currents in transformers

Active Anti - Islanding 1)Communication based schemes 2)Local detection schemes 1a) Transfer Trip Scheme

1b) Power Line Signaling Scheme [2]

2a) Method of impedance measurement [2]

Dynamic Impact of Anti-Islanding Measures Under voltage trip sensitivity  Undervoltages due to faults can lead to unnecessary DG tripping  With extensive DG penetration, simultaneous DG tripping due a fault can cause voltage collapse in the local system (voltage regulation equipment takes time to react)

Positive sequence voltage magnitude for simulations of a system with 45% DG penetration, comparing results for sensitive DG undervoltage tripping to results with less sensitive tripping and no tripping. [1]

Active Anti-Islanding Impact  Degradation of power quality and system stability as DG penetration becomes higher  Currently the local islanding detection methods virtually guarantee that the DG will be unable to provide grid support or improve grid stability when the grid is stressed anti-islanding protection disconnects the DG when it detects voltage and frequency excursions on the grid.  Because of the reclosing practice, anti-islanding techniques must trip DG’s within about 200 milliseconds before the breaker is reclosed. Failure to do so will lead to out-of-phase re-energization of the DG. Failure to do so will lead to out-of-phase re-energization of the DG.

Conclusion  DG penetration levels are not sufficient to cause the problems discussed above.  With the growth of DG, these system issues will be confronted in the future. confronted in the future.  The dynamic performance impact needs to be addressed.  Inadvertent islanding detection schemes not having an undesirable impact on interconnected system performance would be a highly desirable development.

References [1] Distributed Generation Islanding – Implications on Power System Dynamic Performance. R. A. Walling, Senior Member, IEEE, and N. W. Miller, Fellow, IEEE [2] An Assessment of DG Islanding Detection Methods and Issues for Canada July, 2004 CETC-Varennes (TR) 411-INVERT CETC-Varennes (TR) 411-INVERT [3] Islanding Detection Method of Distributed Generation Units Connected To Power Distribution System. J.E.Kim, Member IEEE, J.S.Hwang

Questions / Comments ? Questions / Comments ?