1. Frankfurt (Germany), 6-9 June 2011  PV in Spain: Basically Large plants connected to MV or HV Mainly in rural areas (generation exceeds consumption) 3,000 MW in 2007 and 2008  Operational experience: Islanding behaviour during network maintenance or faults Overvoltages in PV plants, causing damages (CIRED 2009)  Field tests in large PV plants connected to Iberdrola’s networks, to reproduce both cases. F.J. Pazos – Spain – Session 4 – Paper 0184 Operational experience and field tests on islanding events caused by large photovoltaic plants

2. Frankfurt (Germany), 6-9 June 2011  Experience: Dangerous work conditions Impossibility of network operation or maintenance Failure of network automation Damaged inverters F.J. Pazos – Spain – Session 4 – Paper 0184 Islanding events

3. Frankfurt (Germany), 6-9 June 2011  Failure of anti-islanding protections during maintenance of a MV/LV substation  Safety golden rules: 1. Isolate working area 2. Lock isolation 3. Voltage verification…  Increased risk: electric arc across a switch (2) not designed for load breaking. F.J. Pazos – Spain – Session 4 – Paper 0184 Dangerous work conditions

4. Frankfurt (Germany), 6-9 June 2011  Solution for dangerous work conditions: Additional voltage absence verification, before MV switching.  Consequence: Maintenance works could not be carried out  No access to switching devices within PV plants  Dispersed PV plants, several km away from the working area F.J. Pazos – Spain – Session 4 – Paper 0184 Impossibility of network operation or maintenance

5. Frankfurt (Germany), 6-9 June 2011  Breakers with synchronism or voltage absence verification cannot close Voltage in the islanding network looses synchronism with the network Normal service cannot be restored Further actions to identify and disconnect voltage source. F.J. Pazos – Spain – Session 4 – Paper 0184 Failure of network automation

6. Frankfurt (Germany), 6-9 June 2011  Breakers without voltage verification Breakers will close although PV is still generating Overcurrent, harmful for inverter IGBT. Some cases of fatal damages, affecting up to 100% of the inverters of a large PV plant.  Frequent case: Earth fault in MV feeder (difficult to detect in LV) Followed by fast reclosing (from 0.4 to a few sec.)  Solution: Extremely fast internal overcurrent protection in inverters. F.J. Pazos – Spain – Session 4 – Paper 0184 Damaged inverters

7. Frankfurt (Germany), 6-9 June 2011  Islanding events have to do with the interaction between inverters and loads. The system tends to find a stable point, mainly by voltage adjustment (not so much by frequency) Possible with some generation-consumption imbalance (10%) They can last long time. F.J. Pazos – Spain – Session 4 – Paper 0184 Field tests Voltage & frequency during islanding

8. Frankfurt (Germany), 6-9 June 2011  Failure of anti-islanding systems due to interaction between several inverters Actual field situation is not represented by laboratory tests. Failures with several inverters of the same brand Failures with several inverters of different brands 5 inverter brands tested  From several countries  With different anti-islanding methods (passive and active) F.J. Pazos – Spain – Session 4 – Paper 0184 Field tests

9. Frankfurt (Germany), 6-9 June 2011  Coordination between protections: Included in the inverters (active or passive methods) Protections of the point of coupling (relays) Communication based protections  Fast: intertripping  Slow: based on telecontrol  New developments  Coordination of requirements from Transmission and Distribution System Operators TSO: delayed or insensitive trip to prevent instability DSO: fast and certain trip, to prevent damages or affecting power quality F.J. Pazos – Spain – Session 4 – Paper 0184 Solution: COORDINATION

10. Frankfurt (Germany), 6-9 June 2011  Coordination between inverter manufacturers (standards) Improve anti-islanding tests In more real conditions (several inverters in parallel) F.J. Pazos – Spain – Session 4 – Paper 0184 Solution: COORDINATION

11. Frankfurt (Germany), 6-9 June 2011  DER connected to MV/HV, give priority to system stability FRT capabilities Passive protections (internal or at the point of coupling) Communication based protections.  In general, telecontrol for safe maintenance works  Occasionally: intertripping.  DER connected to LV: give priority to safety and lower communication requirements Telecontrol by means of smart meters with internal switch  With FRT Fast active and multi-inverter methods when telecontrol is not available.  Without FRT F.J. Pazos – Spain – Session 4 – Paper 0184 Proposal: Segmentation

12. Frankfurt (Germany), 6-9 June 2011 F.J. Pazos – Spain – Session 4 – Paper 0184 Thank you for your attention