# Ensuring Stable Operation of Wind Farms Connected to Distribution Networks
## 1 Introduction  
The growing number of generation facilities based on renewable energy sources (RESs) and their increasing total capacity in the structure of generating capacities have set new goals for the global energy community to ensure their stable operation and manage electric power systems [1, 2]. The intensive development of generation based on renewable energy sources is due to its high energy and environmental efficiency; the intention to reduce dependence on gas, oil, and coal imports from other countries; and a decrease in specific capital costs for their construction [3, 4]. The reports by Bloomberg NEF and the United Nations Environment Program note that over the past 10 years, the number of generating capacities commissioned at windfarms and solar power plants has exceeded the number of those at any other energy sources [5]. Forecasts of the development rates of electricity generation based on renewable energy sources show that their share in electricity generation will increase to 27.1% by 2030 and to 48.8% by 2050. In 2030, wind farms will prevail in the generation mix based on renewables and will make up 70%, but by 2050 their share will go down to 47% due to a rise in the share of solar power plants with highly efficient photovoltaic modules [6]. Some countries of the world are planning to complete the transition of the electricity supply of consumers to renewable energy generation, for example, in Sweden by 2040 [7] and in Canada by 2050 [8]. The connection of type IV wind turbines to the wind farm collection network is carried out through inverters. They implement all the functions of automatic control and protection of wind turbines from unacceptable emergency and abnormal conditions. According to practical experience, the inverter protection settings comply with the requirements of the grid codes of the countries where they are designed and/or manufactured [9; 10]. An analysis of the causes of wind turbine shutdowns suggests that they occur in case of short circuits (SCs) in the distribution network, which are cleared by the action of backup protections with time delays of 1-2 s and are accompanied by voltage dips. This decreases the power generated by wind farms to \"zero\", increases the load of the generating units of conventional power plants, power transmission lines (TLs), and power transformers, and causes the disconnection of electricity to consumers [11; 12; 13]. The grid codes of different countries contain a requirement to ensure the stable operation of wind turbines during short-term voltage dips on any or all phases in accordance with the voltage-time low voltage ride through (LVRT) characteristic. This can prevent unnecessary shutdowns of wind turbines with the correct operation of relay protection devices in distribution networks [14; 15]. The distribution networks in this article include electric networks with a voltage up to 220 kV inclusive. The regulations in some countries lack the approved form of the voltage-time LVRT characteristic for wind turbines. In this case, when designing a wind farm, it is impossible to perform a simple comparison of the voltage-time LVRT characteristic given by the current grid code with the voltage-time LVRT characteristic set by the manufacturer for a wind turbine. At the same time, the grid codes of some countries have a requirement that wind turbines should not be disconnected from the distribution network during standard disturbances accompanied by voltage sags. The lists of typical disturbances however are country-specific and the parameters of voltage dips (duration and depth) depend on the topology of the distribution network; the high-voltage circuit breakers used; and relay protection devices, their operation algorithms, and settings. This study aims to analyze the causes of excessive shutdowns of wind turbines during standard disturbances in distribution networks and to present a methodology for checking the settings of the LVRT characteristic for compliance with the requirements for wind turbines.