Transcript Operational experience and field tests on islanding events caused

Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
Dangerous work conditions



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
132/20 KV SUBSTATION
1. Open circuit breaker
2. Open and lock switch
PV 1
PV 2
3. Voltage
verification
in the
working
area
Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
Damaged inverters

Breakers without voltage verification




Frequent case:



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.
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
Frankfurt (Germany), 6-9 June 2011
Voltage & frequency
during islanding
Field tests

ISLANDING
F.J. Pazos – Spain – Session 4 – Paper 0184
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.
Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
Solution: COORDINATION

Coordination between inverter manufacturers (standards)
 Improve anti-islanding tests
 In more real conditions (several inverters in parallel)
DC power
source
(PV)
DC power
source
(PV)
VDC
PDC/2
VDC
PDC/2
EUT
(inverter)
1
Similar
micro gen
erator
F.J. Pazos – Spain – Session 4 – Paper 0184
Frankfurt (Germany), 6-9 June 2011
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
Frankfurt (Germany), 6-9 June 2011
Thank you
for your attention
F.J. Pazos – Spain – Session 4 – Paper 0184