EVALUATION OF ANTI-ISLANDING
PROTECTION SCHEMES
INDIAN CONTEXT
Renewable Energy World India
Kona Eswararao | Gamesa R&D Chennai
New Delhi / 21 April 2012
EVALUATION OF ANTI - ISLANDING
SCHEMES
Distributed Generation
Islanding
Anti-Islanding protection
Passive schemes and NDZ
PJD applied to weak grid
Simulation results
Conclusion
Anti-Islanding Protection
2
Distributed Generation
Introduction and advantages
► Distributed Generation (DG) is utilizing the generated power at the same location where it
is produced keeping the fact in mind that RE plants are having less generation capacity
compared to conventional power plants.
► Power loss due to transmitting power to the grid is reduced
► Remote locations can be electrified with DG
3
Power
Converter
Pgrid + jQ grid
PCC
PDG + jQDG
Utility breaker
Pload + jQload
Grid
Pgrid = ∆P = PDG − Pload
Wind Turbine
Generator
Q grid = ∆Q = QDG − Qload
R
L
C
Local Load
Anti-Islanding Protection
Grid Connected RE Systems
Challenges and Issues
►Islanding
►Dynamic interaction between various generators
►Conflict in voltage control for generators in
proximity
►Power Quality
► Weak Grid situations
Anti-Islanding Protection
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Islanding
Introduction
► When loads are being fed power from DG even after the power supply is
suspended from utility - Islanding Condition at PCC
Power
Converter
Pgrid + jQ grid
PCC
PDG + jQDG
Utility breaker
5
Pload + jQload
Grid
Pgrid = ∆P = PDG − Pload
Wind Turbine
Generator
Q grid = ∆Q = QDG − Qload
R
L
C
Formation of Island
when breaker is opened
Local Load
Anti-Islanding Protection
Islanding
Issues
►Danger to maintenance and restoration personnel
►Destruction at both customer and utility side equipment
6
►Power quality of DG becomes worsen - adversely affect the
loads
►Automatic closing of utility breaker may create a condition of
asynchronous closure
Anti-Islanding Protection
Anti-Islanding
Classification
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Anti-Islanding Protection
Anti-Islanding
Passive and Active Schemes
► Passive techniques are based on measurement of instantaneous voltage,
frequency and phase deviations at PCC
► Simple and Easy to implement
► No introduction of noise or harmonic signal into network as like as Active
methods – Power Quality not disturbed
► The range of active power and reactive power change during islanding will
influence the detection time
► Passive techniques relay on certain distinct pattern or signatures at the DG
out put
► Active techniques introduce deliberate changes or disturbances into the
connected circuit and then observe the response
Anti-Islanding Protection
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Anti-Islanding
NDZ for CERC and C-WET requirements
NDZ for CERC Tolerance at 33 KV
10
At Qf = 1.63
At Qf = 2.5
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% Change in Reactive power
► Non Detection Zone (NDZ) is the range active
power and reactive power mismatch that
causes non detection of Islanding
► In this work NDZ is calculated for CERC and
CWET based on voltage and frequency
variation allowed
6
4
OF
2
-2
-4
-6
UF
-8
-10
-30
PARAMETER
CERC at 33 KV
CWET at 33 KV
Vmax
36 KV
36 KV
UV
OV
0
-20
-10
0
10
% Chnage in Active power
20
30
NDZ for CWET Tolerance at 33 KV Grid
30
Vmin
30 KV
30 KV
At Qf = 1.63
At Qf = 2.5
fmax
50.2 Hz
51.5 Hz
fmin
49.5 Hz
47.5 Hz
% change in P -15.9 % to 21% -15.9 % to 21%
% change in Q
-3.3% to 1.29 % -17.6% to 9.35%
for Qf = 1.63
% change in Q
-5.07% to 1.98% -27% to 14.34%
for Qf = 2.5
Anti-Islanding Protection
% Change in Reactive powr
20
OF
10
0
OV
UV
-10
-20
-30
-30
-20
-10
UF
0
10
% Change in Acitve power
20
30
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Phase Jump Detection (PJD)
Well known method of Anti-Islanding
► PJD is a passive protection method in which phase angle is computed by
using an algorithm, when phase angle is beyond the threshold limit then
Islanding is said to be happen
► This method do not disturb the power quality as like in active methods
► Easy implementation
10
Observes the phase difference between the inverter voltage
and current when there is an abrupt jump in the PCC voltage.
Anti-Islanding Protection
PJD Application
Stiff Grid condition
Islanding detection at stiff grid
2
1
Phase jump in radians
► MATLAB simulation model is developed to
analyse PJD method applied for stiff grid
situation
► Islanding detection time for stiff grid is
23.5 msec
Stiff grid
1.5
0.5
0
-0.5
-1
11
-1.5
-2
0
0.05
0.1
Time in sec
0.15
0.2
Islanding detection at stiff grid
Stiff Grid
1
X: 0.07355
Y: 1
DG CB status
0.8
0.6
0.4
0.2
0
Anti-Islanding Protection
0
0.02
0.04
0.06
0.08
0.1
0.12
Time in sec
0.14
0.16
0.18
0.2
PJD Application
Weak Grid condition – Voltage fluctuations
► Same PJD method is applied to various weak grid situations
► Detection time with high voltage fluctuations is 16 msec - Very QUICK
Islanding detection during high grid voltage
1
X: 0.06605
Y: 1
0.9
X: 0.07355
Y: 1
0.8
Stiff grid
Vhigh50
Vhigh20
Vhigh10
DG CB status
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.06
0.065
0.07
Time in sec
Anti-Islanding Protection
0.075
0.08
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PJD Application
Weak Grid condition – Frequency fluctuations
► Detection time same as stiff-grid, effect is negligible – Because of
frequency variation doesn’t contribute to phase angale detection
Islanding detection during high grid frequency
1
Stiff Grid
fhigh10
fhigh20
fhigh50
X: 0.07355
Y: 1
0.9
0.8
DG CB status
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.07
0.071
0.072
0.073
0.074
Time in sec
Anti-Islanding Protection
0.075
0.076
0.077
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PJD Application
Weak Grid condition – Higher THD presence
► Same Islanding detection as compared to stiff grid due to grid already
has harmonics / disturbance
► Detection time with high harmonics in the system is just 14 msec –
Faster detection
Islanding detection during 5th harmonics in grid
1
X: 0.06425
Y: 1
0.9
Islanding detection during 11th harmonics in grid
ideal
X: 0.07355
Y: 1 THD 10%
0.9
THD 20%
THD 50%
0.8
0.8
0.7
X: 0.0622
Y: 1
Stiff Grid
THD 10%
THD 20%
THD 50%
X: 0.07355
Y: 1
0.7
0.6
DG CB status
DG CB status
14
1
0.5
0.4
0.3
0.6
0.5
0.4
0.2
0.3
0.1
0.2
0
0.1
0.06
0.062
0.064
0.066
0.068
0.07
Time in sec
0.072
0.074
0.076
0
0.06
Anti-Islanding Protection
0.065
0.07
0.075
Time in sec
0.08
0.085
Conclusions
► Introduction to DG Islanding phenomenon
► Need for Islanding protection – stringent Grid codes
► Passive methods are simple, cost effective but higher values of NDZ
► PJD gives early detection of Islanding when grid is weak
Anti-Islanding Protection
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Thank you
16
Q&A
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Anti-Islanding Protection