# Ensuring Stable Operation of Wind Farms Connected to Distribution Networks
## 5 Discussion  
International experience suggests that over the past decade, different countries have gradually tightened the requirements for the connection and operation of wind farms within electric power systems.  
Mass shutdowns of wind turbines during standard disturbances in the distribution network can lead to an emergency increase in the load for the generating units of conventional power plants, power transmission lines, and power transformers, thereby causing heavy-load conditions [60; 61; 62].  
A list of standard disturbances to be analyzed to design the wind power evacuation arrangement in individual countries may differ significantly from the requirements of the grid codes of the countries where the wind turbines are designed and/or manufactured.  
Manufacturers of type IV wind turbines must adapt the LVRT characteristics to the requirements of the grid code of the country where the wind turbine is delivered or technical solutions will have to be implemented by the owner of the wind farm.  
To confirm the compliance of wind turbines with the requirements of the grid code of a particular country, it is necessary to calculate transient processes and simulate standard disturbances. The purpose of this is to compare the results of calculations of the residual voltage at the outputs of wind turbine inverters with the settings for the LVRT characteristic. The analysis should be carried out in the three operating zones discussed in the paper. The countries where the grid codes have no requirements to set the LVRT characteristic and ensure the injection of reactive current, and the rate of its rise in the event of a voltage dip at the output of wind turbine inverters, should introduce them.  
Analyzing the transient calculation results produces the following conclusions about the performance of various methods for preventing wind turbine outages:  
* The modernization of relay protection devices by the replacement of electromechanical devices with digital ones can reduce the response time of the second and third stages of backup protections to 0.9-1.0 s. In addition, the second sets of relay protection devices with absolute selectivity should be used as backup protections with automatic introduction of accelerated stepped protections.
* The activation of the wind farm reactive current injection function, which can be incorrectly set, and in some cases disabled, makes it possible to increase the residual voltage at the output of the wind turbine inverters with a short-circuit duration of up to 0.2s and prevent unnecessary shutdowns of the wind turbine.
* The application of STATCOM is ineffective for the stable operation of wind turbines under standard disturbances in the distribution network due to the narrow range of operating voltage, 80% \(U_{\text{nom}}\leq U_{\text{oper}}\leq 120\%\)\(U_{\text{nom}}\).
* The series connection of CLR in the circuit of the 35/110 kV step-up transformer of a wind farm is effective as it increases the residual voltage at the outputs of inverters of the wind turbines and prevents their excessive shutdowns. In each case of wind farm connection to the distribution network, \(X_{\text{CLR}}\) should be determined based on the results of transient calculations.
* The most effective technical solution is to make changes to the hardware of wind turbine inverters and install a block of supercapacitors and a DC-DC converter. This enables the adjustment of the operating range of the LVRT characteristic and prevents unnecessary shutdowns of the wind turbine under any type of standard disturbances. At the same time, there is no need to upgrade relay protection devices and automatic controls in the distribution network.