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PV in Spain: Basically Large plants connected to MV or HV

Operational experience and field tests on islanding events caused by large photovoltaic plants. 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:

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PV in Spain: Basically Large plants connected to MV or HV

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  1. Operational experience and field tests on islanding events caused by large photovoltaic plants • 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

  2. Islanding events • Experience: • Dangerous work conditions • Impossibility of network operation or maintenance • Failure of network automation • Damaged inverters F.J. Pazos – Spain – Session 4 – Paper 0184

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

  4. Impossibility of network operation or maintenance • 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

  5. Failure of network automation • 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

  6. Damaged inverters • 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

  7. Field tests Voltage & frequency during islanding • 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

  8. Field tests • 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

  9. Solution: COORDINATION • 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

  10. Solution: COORDINATION • 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

  11. Proposal: Segmentation • 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

  12. Thank you • for your attention F.J. Pazos – Spain – Session 4 – Paper 0184

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