Download DISTRIBUTED GENERATION ISLANDING

DISTRIBUTED GENERATION ISLANDING - IMPLICATIONS ON
POWER SYSTEM DYNAMIC PERFORMANCE
Sandhya P Prabhu
April 19, 2006
What is islanding ?
Figure 1 Typical distributed system with DG’s [2]
Figure 1 Typical distributed system with DG’s [2]
Implications of unintentional islanding
• Hazard to utility line workers and public
• Damage 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 grid
Out - Phase – Reclosing
• What is reclosing / out – of – phase reclosing?
• Produces 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.
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.
 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 2004-074 (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 ?