Development of Grid Code for Wind Power Generation in India Powerpoint

INDIAN WIND GRID CODE

Rajesh KatyalUnit Chief, R&D

Centre for Wind Energy Technology

CENTRE FOR WIND ENERGY TECHNOLOGYCHENNAI

OVERVIEW

CENTRE FOR WIND ENERGY TECHNOLOGY

NEED FOR INDIAN WIND GRID CODE Wind energy constitutes 6% of the installed capacity

in the power scenario in India.

Wind turbines are installed in windy sites, which maynot have strong grids.

Local impacts like voltage fluctuations, flicker,reactive power absorption when the penetration islow.

With high penetration, overall power system getsaffected.

Grid code envisages to establish a standard operatingpractice for wind turbines to minimise these impactsand reap maximum benefits.


ELECTRICAL SYSTEM IN WIND TURBINES



Fixed speed wind turbine



Variable speed wind turbine with full-scale frequencyconverter


GRID BEHAVIOUR OF WIND TURBINES

Majority of wind turbines use induction generators, unlikethe conventional generators which are synchronous

Induction generators need VAR support, for which capacitorbanks are provided.

Inadequate reactive power support will lead to drawal fromgrid, and affect the voltage profile at the point ofinterconnection.

Wind turbines using synchronous generators do not needreactive power support, but may have to deal with otherissues like harmonics.

Grid code sets a standard operating practice for differenttype of generators.


GRID BEHAVIOUR OF WIND TURBINES

Wind turbines disconnect from the grid whenvoltage at the point of connection drops

Wind turbines can remain connected to the gridduring a fault, only if adequate reactive powersupport is provided.

Wind is variable in nature, hence wind generationcannot be scheduled.


WORLD SCENARIO

Grid Codes have been enforced for countries likeUSA, Germany, Spain, Denmark, China, NordicCountries, Canada and Ireland, which havesubstantial wind generation.

The grid codes for wind, in general deal with thefollowing technical requirements: Active power control Frequency Voltage and reactive power issues Fault ride through capability Protection Power quality issues like flicker, harmonics etc.


GRID CODE REQUIREMENTS


GRID CODE REQUIREMENTS


Variation of active power output of wind farms with respect to frequency (as proposed in Grid Code)

GRID CODE REQUIREMENTSFREQUENCY REQUIREMENTS: System frequency is a major indicator of the power balance

in the system.

A decrease in generation vis-a-vis the demand causes thefrequency to drop below the nominal frequency and viceversa.

This imbalance can be mitigated by primary control andsecondary control of conventional synchronous generators.

High penetration of wind turbines can have a significantimpact on the frequency of the grid.

Power output of the wind turbine can be regulated duringhigh frequency.


GRID CODE REQUIREMENTSVOLTAGE AND REACTIVE POWER ISSUES:

Wind turbines with induction generators needreactive power support.

Capacitor banks are the preferred method ofreactive power compensation in wind farms.

Reactive power drawl from the system can causeincreased losses, overheating and de- rating ofthe lines.

Doubly fed induction generators and synchronousgenerator based wind turbines do not have anyconstraints with respect to reactive power.


GRID CODE REQUIREMENTSREACTIVE POWER ISSUES:The wind farm should maintain a power factor of 0.95 lagging to 0.95 leading

Voltage Vs Power factor characteristics of wind farms connected above 66 kV


GRID CODE REQUIREMENTSFAULT / LOW VOLTAGE RIDE THROUGH:

Ability of the wind turbine to remain connected to the grid without trippingfrom the grid for a specified period of time during a voltage drop at the pointof connection.

period of fault ride through depends on

magnitude of voltage drop at the Point of Common Coupling (PCC)during the fault

time taken by the grid system to recover to the normal state.

During system disturbances, if generators of large generating capacityconnected to the grid continue their operation, this aids the system inreturning to normal operation.

During a fault that causes a voltage drop at the wind turbine terminals, thereactive power demand of induction generators increases. Unless a reactivepower support is available at the generator terminals, the reactive power willbe drawn from the grid and further instability.


GRID CODE REQUIREMENTSFAULT / LOW VOLTAGE RIDE THROUGH (AS PER IWGC):

Vf : 15% of nominal system voltageVpf : Minimum Voltage for normal operation of the wind turbine

Nominal system voltage (kV)

Fault clearing time, T(ms)

Vpf (kV)

Vf(kV)

400 100 360 60.0

220 160 200 33.0

132 160 120 19.8

110 160 96.25 16.5

66 300 60 9.9

Table 3: Fault clearing time and voltage limits


GRID CODE REQUIREMENTSWIND FARM PROTECTION:

The relay protection system of the wind turbine should take in to account: Normal operation of the system and support to network duringand after the fault. Secure wind farms from damage originating from faults in the

network.

Minimum requirement with respect to wind farm protection (IWGC): under/over voltage protection under/over frequency protection over current and earth fault protection load unbalance (negative sequence) protection differential protection for the grid connecting transformer capacitor bank protection tele-protection channels (for use with distance protection) between the

grid connection point circuit breaker and user connection point circuitbreaker.


GRID CODE REQUIREMENTSPOWER QUALITY ISSUES:

Power Quality

Ability of a power system to operate loads, without damaging ordisturbing them, a property mainly concerned with voltage quality at pointsof common coupling & Ability of the loads to operate without disturbing orreducing the efficiency of the power system, a property mainly, but notexclusively, concerned with the quality of current waveform

Assessment of power quality of wind farms IEC 61400-21: Wind TurbineGenerator Systems, Part 21: Measurement and Assessment of PowerQuality Characteristics of Grid Connected Wind Turbines


GRID CODE REQUIREMENTSFLICKER:

Visual fluctuations in the light intensity as a result of voltage fluctuations (1-10Hz)

Caused during continuous operation: by tower

shadow of wind turbine (1 2 Hz) Switching operation : by power

fluctuations (both active and reactive power)

Not a main concern for variable speed turbines.

IWGC requirement : IEC 61000-3-7 : for voltage flicker

limits. IEC 61000-4-15 :Guidelines on

measurement of flicker.


GRID CODE REQUIREMENTSHARMONICS:

Generated by variable speed turbines with powerconverters, like doubly fed generator and full variablespeed wind turbine.

IEC 61400-21 recommends measurement of harmonicemissions only for variable speed turbines.



Total harmonic distortion of voltage,

where Vn: nth harmonic of voltageV1: fundamental frequency

(50 Hz) voltage

SystemVoltage(kV)

TotalHarmonicDistortion

(%)

Individual Harmonic of any Particular frequency (%)

765 1.5 1.0

400 2.0 1.5

220 2.5 2.0

132 3.0 2.0

Voltage harmonic limits



Harmonic content of the supply current :

Where In: nth harmonic of currentI1: fundamental frequency

(50 Hz) current

Current harmonic limits (IWGC)

Voltage level

69 kV

ITHD 5% 2.5%


GRID CODE REQUIREMENTSVOLTAGE UNBALANCE:

Ratio of the deviationbetween the highest andlowest line voltage to theaverage of the three linevoltages.

Can cause negative sequencecurrent to flow in the rotor ofthe generator and affect itsperformance

same voltage requirementsfor unbalance as forconventional generators.

Voltage level (kV)

Unbalance (%)

400 1.5

220 2

REQUIREMENTS OF IWGC

Planning Code for transmission systems evacuating wind power

Connection code for wind farms

Operating code for wind farms


PLANNING CODE FOR TRANSMISSION SYSTEMS EVACUATING WIND POWER

Wind power evacuation should be a part of the overall grid planning.

Planning criterion for wind: System peak load with high wind generation System light load with high wind generation Local light load with high wind generation


PLANNING CODE FOR TRANSMISSION SYSTEMS EVACUATING WIND POWER

N-1 contingency criteria :Wind farms connected above 220 kV or of capacity 100 MW and above at 220 kV levels.

The Wind power addition plan for every five years issued by the Ministry of New and Renewable Energy to be considered for planning of transmission lines.


CONNECTION CODE FOR WIND FARMS

Minimum technical standards to be adopted for wind turbines

Voltage withstand limits for wind farms

Voltage (kV)

Nominal % Limit of variation Maximum Minimum

400 +5% to -10% 420 360220 +11% to -9% 245 200132 +10% to -9% 145 120110 +10% to -12.5% 121 96.2566 +10% to -9% 72.5 6033 +5% to -10% 34.65 29.7



Frequency tolerance range47.5 51.5 Hz. Beyond this: manufacturer specific.

Wind farms shall be able to withstand change in frequency up to 0.5 Hz/sec.



Voltage unbalance

Reactive power capability

Active power control

Low voltage ride through

Protection schemes for wind farm protection


OPERATING CODE FOR WIND FARMS For safe and reliable operation of grid

Operating voltage limits for wind farms

Voltage (kV)

Nominal % Limit of variation Maximum Minimum

400 +5% to -10% 420 360220 +11% to -9% 245 200132 +10% to -9% 145 120110 +10% to -12.5% 121 96.2566 +10% to -9% 72.5 6033 +5% to -10% 34.65 29.7


OPERATING CODE FOR WIND FARMSFrequency of operation for wind farms

Shall not be started above 51.5 Hz.


OPERATING CODE FOR WIND FARMS

Reactive power and voltage control VAR drawl from the grid at voltages below 97 % of

nominal will be penalized.

VAR injection into the grid at voltages below 97 % of nominal will be given incentive.

VAR drawl from the grid at voltages above 103 % of nominal will be given incentive.

VAR injection into the grid at voltages above 103 % of nominal will be penalized


OPERATING CODE FOR WIND FARMSRamp rate limits Aims at regulating the active power generated from the WTG and

minimizing the sudden variations in generated power due tovariations in the wind.

Wind Farm installed capacity (MW)

10 min Maximum Ramp (MW)

1 min Maximum Ramp (MW)

50-150 Installed Capacity/1.5

Installed Capacity/5

>150 100 30

Ramp rate limits for wind farms



Flicker IEC 61000-3-7 : for voltage flicker limits. IEC 61000-4-15 :Guidelines on measurement of flicker.

Harmonics Voltage harmonic limits : as per Indian Electricity Grid

Code

Current harmonic limits: IEEE STD-519-1992



Operation during transmission congestion As per instructions of system operator. Wind shall be considered like overflowing reservoir in Merit Order

Dispatch

Demand estimation Wind Energy Forecasting-

Day ahead forecast: for assessing the probable wind energy that can be scheduled for the next day.

Hourly forecast :To minimize the forecasting error that can occur in the day ahead forecasting.


SUMMARY

Grid code brings wind at par with conventionalgenerators.

Technical requirements have been appropriatelyrecommended for small wind farms and large windfarms.

Conditions like fault ride through capability andforecasting to be implemented taking into accountthe penetration levels of wind energy, cost ofimplementation, tariff structure and usefulness interms of grid management strategies.


Indian Wind Grid CodeOverviewNeed for Indian Wind Grid CodeElectrical system in wind turbinesElectrical system in wind turbinesElectrical system in wind turbinesGrid behaviour of Wind TurbinesGrid behaviour of Wind TurbinesWorld ScenarioGrid Code RequirementsGrid Code RequirementsGrid Code RequirementsFrequency requirements:Grid Code RequirementsVoltage and reactive power issues:Grid Code RequirementsReactive power issues:Grid Code RequirementsFault / low voltage ride through:Grid Code RequirementsFault / low voltage ride through (as per IWGC):Grid Code RequirementsWind farm protection:Grid Code Requirements Power quality issues:Grid Code RequirementsFlicker:Grid Code RequirementsHarmonics:Grid Code RequirementsHarmonics:Grid Code RequirementsHarmonics:Grid Code RequirementsVoltage unbalance:Requirements of IWGCPlanning Code for transmission systems evacuating wind power Planning Code for transmission systems evacuating wind power Connection code for wind farmsConnection code for wind farmsConnection code for wind farmsOperating code for wind farmsOperating code for wind farmsOperating code for wind farmsOperating code for wind farmsOperating code for wind farmsOperating code for wind farmsSummarySlide Number 37

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Development of Grid Code for Wind Power Generation in India Powerpoint