CENTRE FOR WIND ENERGY TECHNOLOGY CHENNAI INDIAN WIND GRID CODE

Transcription

1 CHENNAI INDIAN WIND GRID CODE Rajesh Katyal Unit Chief, R&D Centre for Wind Energy Technology

2 OVERVIEW

3 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 may not have strong grids. Local impacts like voltage fluctuations, flicker, reactive power absorption when the penetration is low. With high penetration, overall power system gets affected. Grid code envisages to establish a standard operating practice for wind turbines to minimise these impacts and reap maximum benefits.

4 ELECTRICAL SYSTEM IN WIND TURBINES

5 ELECTRICAL SYSTEM IN WIND TURBINES Fixed speed wind turbine

6 ELECTRICAL SYSTEM IN WIND TURBINES Variable speed wind turbine with full-scale frequency converter

7 GRID BEHAVIOUR OF WIND TURBINES Majority of wind turbines use induction generators, unlike the conventional generators which are synchronous Induction generators need VAR support, for which capacitor banks are provided. Inadequate reactive power support will lead to drawal from grid, and affect the voltage profile at the point of interconnection. Wind turbines using synchronous generators do not need reactive power support, but may have to deal with other issues like harmonics. Grid code sets a standard operating practice for different type of generators.

8 GRID BEHAVIOUR OF WIND TURBINES Wind turbines disconnect from the grid when voltage at the point of connection drops Wind turbines can remain connected to the grid during a fault, only if adequate reactive power support is provided. Wind is variable in nature, hence wind generation cannot be scheduled.

9 WORLD SCENARIO Grid Codes have been enforced for countries like USA, Germany, Spain, Denmark, China, Nordic Countries, Canada and Ireland, which have substantial wind generation. The grid codes for wind, in general deal with the following technical requirements: Active power control Frequency Voltage and reactive power issues Fault ride through capability Protection Power quality issues like flicker, harmonics etc.

10 GRID CODE REQUIREMENTS

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

12 GRID CODE REQUIREMENTS FREQUENCY REQUIREMENTS: System frequency is a major indicator of the power balance in the system. A decrease in generation vis-a-vis the demand causes the frequency to drop below the nominal frequency and vice versa. This imbalance can be mitigated by primary control and secondary control of conventional synchronous generators. High penetration of wind turbines can have a significant impact on the frequency of the grid. Power output of the wind turbine can be regulated during high frequency.

13 GRID CODE REQUIREMENTS VOLTAGE AND REACTIVE POWER ISSUES: Wind turbines with induction generators need reactive power support. Capacitor banks are the preferred method of reactive power compensation in wind farms. Reactive power drawl from the system can cause increased losses, overheating and de- rating of the lines. Doubly fed induction generators and synchronous generator based wind turbines do not have any constraints with respect to reactive power.

14 GRID CODE REQUIREMENTS REACTIVE 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

15 GRID CODE REQUIREMENTS FAULT / LOW VOLTAGE RIDE THROUGH: Ability of the wind turbine to remain connected to the grid without tripping from the grid for a specified period of time during a voltage drop at the point of 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 capacity connected to the grid continue their operation, this aids the system in returning to normal operation. During a fault that causes a voltage drop at the wind turbine terminals, the reactive power demand of induction generators increases. Unless a reactive power support is available at the generator terminals, the reactive power will be drawn from the grid and furtherinstability.

16 GRID CODE REQUIREMENTS FAULT / LOW VOLTAGE RIDE THROUGH (AS PER IWGC): Table 3: Fault clearing time and voltage limits Nominal system voltage (kv) Fault clearin g time, T(ms) Vpf (kv) Vf (kv) V f : 15% of nominal system voltage V pf : Minimum Voltage for normal operation of the wind turbine

17 GRID CODE REQUIREMENTS WIND FARM PROTECTION: The relay protection system of the wind turbine should take in to account: Normal operation of the system and support to network during andafter 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 frequencyprotection over currentand 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 circuit breaker.

18 GRID CODE REQUIREMENTS POWER QUALITY ISSUES: Power Quality Ability of a power system to operate loads, without damaging or disturbing them, a property mainly concerned with voltage quality at points of common coupling & Ability of the loads to operate without disturbing or reducing the efficiency of the power system, a property mainly, but not exclusively, concerned withthe qualityof currentwaveform Assessment of power quality of wind farms IEC : Wind Turbine Generator Systems, Part 21: Measurement and Assessment of Power Quality Characteristics of Grid Connected Wind Turbines

19 GRID CODE REQUIREMENTS FLICKER: 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 : for voltage flicker limits. IEC :Guidelines on measurement of flicker.

20 GRID CODE REQUIREMENTS HARMONICS: Generated by variable speed turbines with power converters, like doubly fed generator and full variable speed wind turbine. IEC recommends measurement of harmonic emissions only for variable speed turbines.

21 GRID CODE REQUIREMENTS HARMONICS: Total harmonic distortion of voltage, where V n : n th harmonic of voltage V 1 : fundamental frequency (50 Hz) voltage Voltage harmonic limits System Voltage (kv) Total Harmonic Distortion (%) Individual Harmonic of any Particular frequency (%)

22 GRID CODE REQUIREMENTS HARMONICS: Harmonic content of the supply current : Current harmonic limits (IWGC) Voltage level <69 kv >69 kv ITHD 5% 2.5% Where I n : n th harmonic of current I 1 : fundamental frequency (50 Hz) current

23 GRID CODE REQUIREMENTS VOLTAGE UNBALANCE: Ratio of the deviation between the highest and lowest line voltage to the average of the three line voltages. Can cause negative sequence current to flow in the rotor of the generator and affect its performance same voltage requirements for unbalance as for conventional generators. Voltage unbalance limits for wind farms Voltage level (kv) Unbalance (%) <220 3

24 REQUIREMENTS OF IWGC Planning Code for transmission systems evacuating wind power Connection code for wind farms Operating code for wind farms

25 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

26 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.

27 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 % to -10% % to -9% % to -9% % to -12.5% % to -9% % to -10%

28 CONNECTION CODE FOR WIND FARMS Frequency tolerance range Hz. Beyond this: manufacturer specific. Wind farms shall be able to withstand change in frequency up to 0.5 Hz/sec.

29 CONNECTION CODE FOR WIND FARMS Voltage unbalance Reactive power capability Active power control Low voltage ride through Protection schemes for wind farm protection

30 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 % to -10% % to -9% % to -9% % to -12.5% % to -9% % to -10%

31 OPERATING CODE FOR WIND FARMS Frequency of operation for wind farms Shall not be started above 51.5 Hz.

32 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

33 OPERATING CODE FOR WIND FARMS Ramp rate limits Aims at regulating the active power generated from the WTG and minimizing the sudden variations in generated power due to variations in the wind. Ramp rate limits for wind farms Wind Farm installed capacity (MW) 10 min Maximum Ramp (MW) 1 min Maximum Ramp (MW) Installed Capacity/1.5 Installed Capacity/5 >

34 OPERATING CODE FOR WIND FARMS Flicker IEC : for voltage flicker limits. IEC :Guidelines on measurement of flicker. Harmonics Voltage harmonic limits : as per Indian Electricity Grid Code Current harmonic limits: IEEE STD

35 OPERATING CODE FOR WIND FARMS 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.

36 SUMMARY Grid code brings wind at par with conventional generators. Technical requirements have been appropriately recommended for small wind farms and large wind farms. Conditions like fault ride through capability and forecasting to be implemented taking into account the penetration levels of wind energy, cost of implementation, tariff structure and usefulness in terms of grid management strategies.

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