evaluation of anti-islanding protection schemes - NPTI

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


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


4

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


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 Classification

7


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


8

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

8 % 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


% 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

9

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


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


0.075

0.08

12

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


0.075

0.076

0.077

13

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


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


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Thank you 16

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