Operation experience of solar power plants connected to the Russian distributed grid

The islanding condition of grid-tied solar power plant with hydro power plant of commensurable power is considered in this article. Based on the results of the article, the relevant conclusions were drawn.


Introduction
The world's power generation trend based on the renewable energy sources keeps on growing year after year [1][2][3][4]: in 2016, the value of the world's investments into renewable energy sources keeps reached 242 BUSD [5]. Keeping in mind wind power and solar power station, by the end of 2016 the global capacity indicators amounted up to 487 GW and 303 GW, respectively [5]. The share of the wind and solar power plant in the world's electric generation output constitutes 4.0% and 1.5%, respectively. By 2020, many countries are planning to increase the renewable energy sources keeps value in terms of the countries power balance up to 15-20%. In accordance with the Russian Federation Government Decree №.1-p dated January 8 th , 2009 and the Russian Federation Government Decree №.449 dated May 28 th 2013, there is an ongoing competitive selection of investment projects purposed for construction of the power generation facilities operated by the renewable energy source [6][7][8][9][10][11][12][13][14][15][16]. Following the results of selecting renewable energy sources keeps projects in 2017 up to 2022, 4.2765 GW electrical power stations should be constructed [17] (Fig.1).

Fig. 1. Renewable energy sources keeps Projects distribution diagram, till 2022
It is obvious that renewable energy sources keeps capacities are expanding year by year, thus increasing its impact on unified electrical grid. The installed generating capacity under renewable energy sources keeps projects ranges within the following figures: wind power plant -Pmax=200.97MW, Pmin=15MW; solar power plant -Pmax=60MW, Pmin=5MW; hydro power plant (hereinafter -hydro power plant) -Pmax=24.9MW, Pmin=5.04MW [17].
At the stage of the Russian renewable energy sources keeps development, the solar power plants are put into operation constructed and operated promptly. The total capacity of the solar power plant commissioned in Russia as of Quarter III 2017 is 460.22 MW that is 0.19% of the installed capacity of Russia [18]. The renewable energy sources keeps impact on the unified electrical grid under normal operating conditions is insignificant due to the incommensurability of solar power plant and unified electrical grid capacities, however, under the normal operating conditions, in some cases, solar power plant has some impact on the electrical regimes.

Solar power plant in isolated operation with hydro power plant
The capacity of Block 1 of Buribaevskaya solar power plant is 10MW. Total of 5 inverter stations are located at the Buribaevskaya solar power plant, each of it has 2 voltage inverters. The voltage inverter unit capacity is 875 kVA with overload capacity up to 1050 kVA. Buribaevskaya solar power plant is connected at the voltage of 10kV using two feeders №2 and №16 substation Buribay. Buribaevskaya solar power plant is not used for primary frequency control.
The capacity of Iriklinskaya hydro power plant is 30 MW. Total of 4x7.5MW generators are located at Iriklinskaya hydro power plant. The Iriklinskaya hydro power plant generators are not used for primary frequency control.
Due to the single-phase short circuit caused by the construction equipment touching the 110 kV transmission lines on 14.07.2016, Iriklinskaya hydro power plant and Buribaevskaya solar power plant were in an isolated operation with the local load was distributed to Stroitelnaya and Buribay substations (Fig.2).  Table 1.  5 Hz, t=0 s Consumption of the local load before the emergency and set off of the automatic emergency response system was ≈23MW. The type of local load was mixed. The major facilities are "Bashkirskaya med" LLC and "Buribaevskiy GOK" LLC that are the largest facilities with 24/7 operation cycle.  b) Due to decrease of frequency down to 48.133Hz, the consumption of the local load of Buribay substation dropped down to ≈6MW, and the consumption dropped by Byzavlyk substation and Ubileynaya substation in the overall amount of ≈5MW. c) Because of the total decrease of the consumed power on ≈11MW and generated power on 6.8MW at 1,700-1,800 ms (Fig.4), frequency got reinstated and stabilized at 50.5-51.1Hz. Because of the reduced frequency, the load of "Bashkirskaya med" LLC decreased to ≈6 MW, the total consumption of the islanding district was ≈12MW. c) The power excess of the Iriklinskaya hydro power plant ≈3MW. d) The frequency increased for three minutes due to the power excess. The frequency ranged up to value of 54.4Hz (Fig.6). 1. The power generation based on renewable energy sources keeps worldwide and in Russia has some positive trends. Every year the production technologies for PV solar modules, inverter equipment and other solar power plant materials improve which results in efficiency growth and prime cost decrease. 2. To study the processes, solar power plant operation with the grid under various regimes shall be modelled. The simulation should take into account the function of voltage inverters: voltage ride through, frequency ride through, reactive current injection during symmetric/asymmetric voltage ride through, reactive current at voltage ride through onset and recovery, active power ramping, reactive power droop function, powerfrequency droop function.