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EFFECT OF HORIZONTAL WIND SHEAR ON FLICKER
EMISSION SEVERITY IN WIND FARM.

EFFECT OF VERTICAL WIND SHEAR ON FLICKER IN WIND FARM
Wednesday, December 11, 2013

1

Power Quality Parameters associated with wind energy …..
Continuity of service
Variation in voltage magnitude.
Short duration variation.
Instantaneous interruption, sag, swell.
Momentary interruption, sag, swell.
Temporary interruption, sag, swell.
Long duration variation.
Interruption.
Under Voltage.
Overvoltage.
Transient voltages and currents.
Voltage unbalance.
Waveform distortion.
DC offset.
Harmonics.
Inter-harmonics.
Notching.
Noise.
Flicker or voltage fluctuations.
Power frequency variations.
Power failure or blackout.

EFFECT OF VERTICAL WIND SHEAR
ON FLICKER IN WIND FARM

2

Input parameters.
Type of generator used for the wind turbine.
Squirrel cage induction generator (SQIG).
Doubly fed induction generator (DFIG).
generator.

Slip ring induction generator (SRIG).
Permanent magnet synchronous generator (PMSG).

DC

Type of the turbine according to the axis of rotation. Horizontal axis.
Vertical axis.
Horizontal axis - Up-Wind Turbines Down-Wind Turbines Shrouded Wind Turbines
Vertical axis wind turbines.
1.Windmill With Rotational Sails ( VAWT ) 2.Neo-Aerodynamic ( VAWT )
3. Darrieus Wind Turbine ( VAWT ) 4. Giromill ( VAWT )
5. Savonius Wind ( VAWT ) continuous and split blade 6. Windstar Turbines ( VAWT )
7. Giromill Wind Turbine( VAWT ) 8. Flapping Panel Wind Turbine( VAWT )
9. The Persian windmill 10. A cup anemometer is a drag-type vertical axis wind turbine
Number of blades of the turbine rotor. One. Two. Three. Six.
Types of blades and Length of blades
Type of turbine according to location of blades - Upwind turbine
Downwind turbine.
Materials of the blades
wood - sensitivity to moisture, high processing costs, low density, low stiffness
glass fiber reinforced plastic (GFRP) - moderate stiffness, high strength, and moderate density.
carbon fiber reinforced plastic (CFRP) - very high stiffness, high strength, light weight& low density.
Aramid fibers - excellent environmental and thermal stability, static and dynamic fatigue resistance
steel aluminum - density about a third that of steel, lightweight, weaker and less stiff than steel.
nickel alloy steels- good corrosion and oxidation resistance.
Types of tower - Steel tubular tower , Lattice tower, Guy wire tower and Height of Tower
Speed of the wind
5 m/s.
10m/s.
15m/s
20m/s
25m/s
Type of load. - Resistive.
Inductive.
Capacitive.
3

INFLUENCE OF HORIZONTAL WIND SHEAR ON
FLICKER EMISSION SEVERITY IN WIND FARM.

Indian Institute of technology Bombay conference
presentation


4

Horizontal wind shear



Horizontal wind shear is a micro scale

meteorological phenomenon, in which there is a swift,
sweeping alteration or disparity in the wind speed,
across the rotor disc, over a comparatively petite
horizontal distance, in the atmosphere in a squat span
of time


Indian Institute of technology Bombay
conference presentation

5

Parameters stirring flicker emission
severity
Tower wake effect

Type of load
Short circuit capacity ratio
Grid parameters
Grid or network impedance phase angle

Dynamics of generator and grid

Tower shadow effect
Blade pitching
. Turbine parameters
Wind turbine type
or characteristics.

Vertical wind shear
Vshr,
Wind parameters

Parameters
stirring flicker
emission
severity

Mean wind speed

Horizontal wind shear

Wind turbulence
intensity



6

Origins of horizontal wind shear.
Low level temperature inversion
Shallow lows

Thunderstorms

Sea breeze

Frontal surfaces
Microbursts


Strong surface winds.
Turbulent air

Snow showers

Mountain waves

Jet streams

Origins of
horizontal
wind shear.

Convective storms


7

Flicker



Tao sun et al. , defined flicker as an imprint of unsteadiness

of visual sensation, induced by a light stimulus, whose
luminance or spectral distribution fluctuates with time, which
can cause clientele’s exasperation.



Flicker is also defined as the measure of voltage deviation,

which may cause brouhaha to consumer.



8

 A typical 600 kW wind turbine has a rotor diameter of 43-44 meters,
i.e. a rotor area of some 1,500 square meters.

 The rotor area determines how much energy a wind turbine is able to
harvest from the wind.
 Since the rotor area increases with the square of the rotor diameter, a
turbine which is twice as large will receive 2 2 = 2 x 2 = four times as
much energy.
 To be considered a good location for
wind energy, an area needs to have
average annual wind speeds of at least 12
miles per hour.

Effect of Flickers…..
Disturbance to photosensitive person.
Light flicker and malfunction of electrical equipment and devices.
Affect the production environment.
Lower work concentration levels.
Detrimental effect on electrical and electronic equipment.
Nuisance tripping due to mis-operation of relays and contactors.
Unwanted triggering of UPS units to switch to battery mode.
Affect industrial processes relying on constant electrical power



10



11

Vertical Wind Shear

Ground


12

Horizontal Wind Shear
Horizontal Wind Shear

╞
Wind
turbine
Wind currents
from top view


13

Type of Wind shear
Wind shear per
second
0-3

Type of wind
shear
Weak

4-5

Moderate

6-7

Large

Above 8

Extreme



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ESTIMATION OF SHORT TERMFLICKER ( PST) AND LONG
TERM FLICKER (PLT) BY POWER QUALITY TEST.







POWER QUALITY TESTS OF WIND TURBINES EXPRESS FLICKER

COEFFICIENT.
FOR EACH WIND TURBINE.
FOR DIFFERENT NETWORK PHASE ANGLE CONDITIONS.
FOR DIFFERENT ANNUAL MEAN WIND SPEEDS
FOR A WIND FARM.



15

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SHORT-TERM FLICKER EMISSION ( PST ) AND LONG TERM
FLICKER EMMISSION (PLT) ARE ASSUMED SAME
PST

AND

PLT

ARE

ASSUMED

SAME

BECAUSE IT IS ASSUMED THAT MEAN
WIND SPEED AND TURBULENCE WILL BE
SAME IN 10 MINUTES AND IN 120 MINUTES.


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SHORT-TERM FLICKER EMISSION ( PST ) AND LONG
TERM FLICKER EMMISSION (PLT)
Wind parameters affecting
Grid parameters affecting
flicker
flicker
Deterministic parameters Short circuit capacity ratio
Mean wind speed / wind (SCR).
speed variation.

Turbine parameters affecting
flicker
Blade pitching.

Wind shear or gradient.
(horizontal and vertical wind
shear)., Tower shadow effect,
tower wake effect.
Stochastic parameters - Wind
turbulence intensity.

Grid / network impedance
angle.

Physical dynamics of wind
turbine

Electrical dynamics of
generator and grid , type of
load

Wind turbine type /
characteristics.


17

17

Wind tunnel for testing



18

WORK DONE - DEVELOPMENT OF MATHRMATICAL
MODEL FOR FLICKER EMMISSION


19

19


SK
Ci
(ΨK)
Va

---

SHORT CIRCUIT CAPACITY.

------

FLICKER COEFFICIENT OF WIND TURBINE i.

----- SPECIFIC NETWORK IMPEDANCE PHASE ANGLE.
----- ANNUAL AVERAGE WIND SPEED FROM SITE.

Sn,i

----

RATED POWER OF WIND TURBINE i.

Nwt

----

NUMBER OF WIND TURBINES IN WIND FARM.



20

20


SK
Ci
(ΨK)
Va

---


------



Sn,i

----


Nwt

----




21

21


SK
Ci
(ΨK)
Va

---


------



Sn,i

----


Nwt

----




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22

SHORT-TERM FLICKER
t
s )

0.1

0.08

0.06

P
(
k
lic
f
m
e
t
r
o
h
S

0.04

Mean wind speed V ( m/s )

0.02

0
0

5

10

Short term flicker ( pst )

15

20

25

Poly. (Short term flicker ( pst ))

30


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23

Proposed Model
Abbreviation

Parameter

N

Number of blades

Nsd

Product of number of turbine blades and multiplying factor

Pst

Short term flicker emission severity (%)

Rbt

Ratio of twice turbine blade length to tower height.

Hshr

Horizontal wind shear ( per second )



24

Assumptions in Model
 The tower is a tubular type of tower as for larger turbines
lattice tower is not favored. Wind turbine considered is of
large size ranging from 1 MW to 7 MW.
 Wind speed variation is in between cut in and cut out
speed. Normally cut in speed is 3 m/s, cut out speed is 25
m/s and rated speed is 11 m/s.
 Turbine is upwind turbine fixed speed turbine . Majority
of the turbines are upwind turbines and downwind
turbines are rarely incorporated.
 Temperature is 25 deg. C. The experiment conducted is a
t 25 deg. C..


25

Variation of flicker due to Horizontal wind shear
Flicker by empirical model for hilly topography and
turbine with 2 blades
Site Saswad ( India)
Flicker by empirical model for flat topography with
grass and turbine with 2 blades
Site : - Nimgaon Mhalungi ( India)
Flicker by empirical model for city region and turbine
with 3 blades
Site : - Lohagaon ( India)
Recorded flicker at hilly topography and turbine with
2 blades
Site :- Saswad ( India)
Recorded flicker at flat topography with grass and
turbine with 2 blades
Site :- Nimgaon Mhalungi ( India)
Recorded flicker at city region and turbine with 3
blades
Site : - Lohagaon ( India)

Hor



26

Conclusion
FLICKER IS NOT A LINEAR SUM OF ALL FLICKERS.



EQUATION TAKES INTO ACCOUNT THE “CANCELLATION” EFFECTS,

WHICH COMES FROM WIND DYNAMICS IN WIND FARM THAT IS NOT
CORRELATED, SO FLICKER IS NOT A LINEAR SUM OF ALL FLICKER
PRODUCED FROM EACH WIND TURBINE.



BECAUSE 3P IS MAIN FLICKER CONTRIBUTION AND THESE

RELATIVELY HIGH FREQUENCIES ARE APPROXIMATELY


UNCORRELATED.

27

27

Mitigations Methods of Flicker elimination Power System
Reactive power compensation equipment and energy
storage equipment.
The Static VAR Compensator (SVC).
Static compensator (STATCOM).
Unified Power Flow Controller (UPFC).



28

References
Pedro Rosas, “Dynamic influences of wind power on
the power system”, Ph.D. Dissertation, Section of
Electric Power Engineering, Orsted Institute,
Technical University of Denmark,. Mar. 2003.
IEC 61400-21, Measurement and assessment of
power quality characteristics of grid connected wind
turbines, International Electrotechnical Commission,
2001


29

THANK YOU.


30

30

LARGE-SCALE INTEGRATION.



LARGE-SCALE INTEGRATION MEANS RELATIVELY

HIGH WIND POWER COMPARED TO LOCAL POWER
SYSTEM (ABOVE 10 % ).



LARGE-SCALE INTEGRATION PROBLEMS ARE

BASED ON SMALL-SCALE ONES.


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TYPES OF LARGE-SCALE INTEGRATION.



LARGE WIND FARMS CONNECTED TO



SEVERAL SMALL WIND FARMS CONNECTED

TRANSMISSION SYSTEM .

TO DISTRIBUTION SYSTEMS.


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POWER QUALITY AND STABILITY ASSESSMENT IN
LARGE-SCALE INTEGRATION OF WIND ENERGY.



DEPENDING ON SIZES, THEY DEMAND SPECIAL

INVESTIGATIONS OF VOLTAGE AND FREQUENCY VARIATIONS
FOR ASSESSMENT OF VOLTAGE STABILITY AND POWER
QUALITY.



IN SMALL-SCALE INTEGRATION, FREQUENCY IS ASSUMED

CONSTANT.


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EFFECTS OF LARGE-SCALE INTEGRATION.



WITH HIGH WIND POWER CAPACITY INSTALLED, LARGE ACTIVE

POWER VARIATIONS CAN INTERACT WITH FREQUENCY CONTROLLERS
IN THE CONVENTIONAL POWER STATIONS, SO FREQUENCY VARIATIONS
CAN OCCUR.



IN ADDITION, LARGE REACTIVE POWER DEMANDED BY WIND FARMS

CAN REDUCE REACTIVE POWER SUPPLY.




HENCE VOLTAGE STABILITY LIMITS CAN BE REDUCED.


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FOCUS- VOLTAGE STABILITY AND
DYNAMIC POWER OSCILLATION.



HERE FOCUS IS ON VOLTAGE STABILITY



DYNAMIC POWER OSCILLATIONS DURING

AND

NORMAL OPERATION OF POWER SYSTEM.


35

35

SINGLE LINE DIAGRAM OF BASIC STRUCTURE
OF POWER SYSTEM.


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EFFECTR OF MEAN WIND SPEED ON
FLICKER FOR FIXED WIND TURBINES .




IN FIXED SPEED WIND TURBINE FLICKER

INCREASES WITH INCREAING WIND SPEED
FLICKER LEVEL INCREASES THREE TIMES

FROM LOWER TO HIGHER WIND SPEEDS.

EFFECT OF VERTICAL WIND SHEAR ON FLICKER IN WIND
FARM

37

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EFFECT WIND SPEED VARIATION ON
POWER



VARIATION IN WIND SPEED OF +/- 1 % GIVE

POWER FLUCTUATION OF +/-20 %

FARM

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FLICKER FOR FIXED AND VARIABLE
SPEED WIND TURBINE



FLICKER IN FIXED SPEED WIND TURBINE IS

MORE FLICKER THAN FOR VARIABLE SPEED
WIND TURBINE.

FARM

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EFFECT OF GRID IMPEDANCE ANGLE ON
FLICKER FOR FIXED WIND TURBINE




FLICKER IN FIXED SPEED IS MORE SENSITIVE TO

GRID ANGLE THAN FOR VARIABLE SPEED
FOR FIXED SPEED WIND TURBINE FLICKER IS MORE

FOR HIGH GRID ANGLES THAN FOR VARIABLE SPEED
VARIABLE SPEED WIND TURBINE
FARM

40

40



ACCEPTABLE FLICKER FOR
TRANSMISION NETWORK
FOR WIND TURBINES CONNECTED TO

TRANSMISSION NETWORK THE FLICKER
CONTRIBUTION FROM WIND TURBINE SHALL BE
LIMITED TO Pst = 0.3 AND BELOW.

FARM

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

ACCEPTABLE FLICKER FOR
DISTRIBUTION NETWORK
FOR WIND TURBINES CONNECTED TO

TRANSMISSION NETWORK THE FLICKER
CONTRIBUTION FROM WIND TURBINE SHALL BE
LIMITED TO Pst = 0.35 AND BELOW.

FARM

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WAYS OF ANALYSIS OF FLICKER




CUMULATIVE PROBABILITY P(l) FUNCTION OF

INSTANTANEOUS FLICKER LEVEL.
SHORT TERM FLICKER SEVERITY VALUE / LONG

TERM FLICKER SEVERITY VALUE.

FARM

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WHY SHORT TERM AND LONG
TERM FLICKER AR SAME







FLICKER IS A FUNCTION OF WIND SPEED.
LOND TERM FLICKER IS MEASURED FOR 2 HOURS I.E. FOR 120

MINUTES.
SHORT TERM FLICKER IS MEASURED FOR 10 MINUTES.
CALCULATIONS OF 12 CONTINUOUS SHORT TERM FLICKER

VALUE IS VERY CLOSE IN 2 HOURS.
SO PLT AND PST ARE SAME


FARM

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INNOVATION IN WORK DONE





FOR FINDING FLICKER FOLLOWING NEW PARAMETER is INTRODUCED
VERTICAL WIND SHEAR/ HORIZONTAL WIND SHEAR.

FLICKER IS ONE OF THE WAY TO EVALUATE THE DYNAMIC PERFORMANCE OF

WIND TURBINE.

FARM

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FLICKER VARIATION WITH
MEAN WIND SPEED

FARM

46

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TURBULENCE INTENSITY

FARM

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47


FARM

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48

GRID IMPEDANCE ANGLE.

FARM

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49

FLICKER VARIATION
TURBULENCE INTENSITY

FARM

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50

THANK YOU.


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