Requirements for Wind Farms (WFs) Grid connection
                   Frequency and Voltage Operation Boundaries
       •   All WTGs should stay connected within the boundary 47.0 - 51.5 Hz 
       •   All WTGs should disconnect with no delay for system frequency < 47Hz 
       •   The disconnection of WTGs for system frequency > 51.5Hz takes place in 4 steps, with a 0.5sec 
           delay between each step
       •   In each step, 25% of the operating WTGs is disconnected 
       •   Applicable to all WFs
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           Requirements for Wind Farms (WFs) Grid connection
                              Active/Reactive Power Boundaries
         Upper diagram : Q-V curve
         •   Within the no-striped area (PF> 0.95) the WF 
             should operate at it’s nominal capacity
         •   Within the striped area (0.835  10 
             MW
      Requirements for Wind Farms (WFs) Grid connection
                 Voltage/Reactive Power Control
    • Upon TSO’s request, the WF should operate in 
      voltage, reactive power or PF control mode
      – Voltage regulation is applied at system connection point 
       (HV/150kV), reactive power and power factor regulation is 
       applied at the MV (20kV) side of WF step up transformer
    • The WF should be equipped with 
      voltage/reactive power regulator according a HV 
      Q–V characteristic 
      – The slope and the reference value Vset (zero reactive power 
       injection at the MV (20kV) side of WF step up transformer are 
       defined by the TSO
    • The desired value of the controlled quantity 
      should be implemented within 30sec after signal 
      receiving
    • speed of regulation response : 
      – in a voltage step change at the connection point (or a 
       step change of reactive power or power factor 
       reference value) the reactive power of the WF should 
       reach 90% of the steady state value in less than 1s
    • Applicable to WFs with installed capacity  > 10 
      MW
      Requirements for Wind Farms (WFs) Grid connection
                   Load-Frequency control
    • At TSO’s command, the WF should 
     change the active power ramp up/down 
     rate (±MW/min)
      – Min and max limits of ramp up/down rates are set 
       by the TSO
      – Active power measurement applies at the MV 
       (20kV) side of WF step up (150/20) transformer 
    • The WF should be equipped with a load-
     frequency controller (characteristic f-P) 
      – Frequency measurement precision ±10mHz 
      – Points Β and Γ define a dead zone within the WF 
       should operate with a constant percentage (% 
       P/Pmax) of the available active power
      – Table values are defined by the TSO
    • TSO’s command for reduction of the 
     production should be implemented 
     within 60s after signal receiving
    • Applicable to WFs with installed capacity  
     > 10 MW
           Requirements for Wind Farms (WFs) Grid connection
                          Low Voltage Ride Through capability
        •  Applicable to all WTGs, voltage is measured at the 
           HV connection point
        •  Disconnection is allowed in area 1 
             –  Reconnection after fault clearance, within 2sec, with a rate 
                10-20% Pmax/sec
        •  Disconnection is allowed in area 2 
             –  Disconnection in 4 steps, with 0.3sec delay between each 
                step, shed 25% of WFs WTGS at each step
             –  Reconnection when the voltage at the connection point (HV) 
                is greater than 142,5kV or 380 kV
        •  After fault clearance, WTGs not disconnected 
           should increase their production with a rate of 10-
           20% Pmax/sec  
        •  Reactive current control 
             –  WTG nominal values Ηare the reference values
             –  For a ±10% Vnom voltage change, the control is activated 
                within 20msec after fault detection
             –  Provision of reactive current ± 2% Ιnom for each ±1% ΔVnom
             –  For voltage sags 50% Vnom , provision of reactive current 
                +100 % Ιnom within 70 msec after fault detection 
             –  Provision of reactive current applies for 500 msec  after 
                voltage recovery within ±10% Vnom band