frankfurt (germany), 6-9 june 2011 pv in spain: basically large plants connected to mv or hv mainly...
TRANSCRIPT
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
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
Frankfurt (Germany), 6-9 June 2011
Failure of anti-islanding protections during maintenance of a MV/LV substation
Safety golden rules:1. Isolate working area2. Lock isolation3. 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 conditions132/20 KV SUBSTATION
PV 2
1. Open circuit breaker
3. Voltage verification
in the working
area
PV 1
2. Open and lock switch
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
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
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
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 testsVoltage & frequency
during islanding
ISLANDING
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
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
Frankfurt (Germany), 6-9 June 2011
EUT (inverter)
1
Similar micro gen
erator
DC power source (PV)
VDC
PDC/2
DC power source (PV)
VDC
PDC/2
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
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
Frankfurt (Germany), 6-9 June 2011
F.J. Pazos – Spain – Session 4 – Paper 0184
Thank youfor your attention