## 2 Structure and Operating Conditions of an Isolated EPS  
The analyzed isolated electrical power system consists of 330 kV open-type switchgear bus-bars and their switching devices; autotransformers, power transformers, and 330 kV open-type switchgear bus-bars, and HVDC converter stations connected to the 330 kV grid and 330 kV overhead lines. EPS part No.1:  
Generation: 1125 MW;  
Generation (inc. HVDC) 1775 MW;  
Consumption: 1630 MW;  
HVDC1: 200 MW (from neighbor to EPS No.1), (nominal value of HVDC1 is 350 MVA);  
HVDC2: 450 MW (from neighbor to EPS No.1), (nominal value of HVDC2 is 650 MVA);  
Balance excess: +200 MW;  
Exchange of electricity values are:  
from EPS No.1 to EPS No.2 (200 MW);  
from neighbor EPS to EPS No.1 (55 MW);  
Generators active power generation of EPS No.1:  
G1 TPP 80 MW (nominal value is 253 MVA), G2 TPP 270 MW (nominal value is 372 MVA), G3 TPP 80 MW (nominal value is 235 MVA), G4 TPP 165 MW (nominal value is 235 MVA), G5 TPP 80 MW (nominal value is 235 MVA), G6 TPP 150 MW (nominal value is 253 MVA);  
Wind power 300 MW (nominal value is 425 MVA);  
The 330 kV substations voltage level varies from 354 kV to 361 kV. EPS part No.2:  
Generation: 850 MW;  
Consumption: 1100 MW;  
Balance deficit: \(-250\) MW;  
Exchange of electricity values are:  
from EPS No.1 to EPS No.2 (200 MW);  
from EPS No.2 to EPS No.3 (0 MW);  
from neighbor EPS to EPS No.2 (50 MW);  
Generators active power generation of EPS No.2:  
G7 TPP 270 MW (nominal value is 531 MVA), G8 TPP 90 MW (nominal value is 105 MVA), G9 HPP 90 MW (nominal value is 105 MVA), G11 HPP 50 MW (nominal value is 150 MVA), G11 HPP 50 MW (nominal value is 150 MVA), G13 HPP 55 MW (nominal value is 75 MVA), G14 HPP 55 MW (nominal value is 75 MVA);  
Wind power 100 MW (nominal value is 210 MVA);  
The 330 kV substations voltage level varies from 355 kV to 360 kV. EPS part No.3:  
Generation: 1000 MW;  
Generation (inc. HVDC) 1400 MW;  
Consumption: 1180 MW;  
HVDC3: 600 MW (from neighbor to EPS No.3), (nominal value of HVDC3 is 700 MVA);  
HVDC4: 200 MW (from EPS No.3 to neighbor), (nominal value of HVDC4 is 500 MVA);  
Balance deficit: \(-220\) MW;  
Exchange of electricity values are:  
from EPS No.2 to EPS No.3 (0 MW);  
from neighbor EPS to EPS No.3 (220 MW);  
Generators active power generation of EPS No.3:  
G15 HPP 200 MW (nominal value is 248 MVA), G16 HPP 25 MW (nominal value is 29 MVA), G17 HPP 25 MW (nominal value is 29 MVA), G18 TPP 400 MW (nominal value is 524 MVA);  
Wind power 350 MW (nominal value is 475 MVA);  
330 kV substations voltage level varies from 356 kV to 360 kV. The scheme of the isolated power system is presented in Figure 1.  
In numerical simulation it was assumed that operating conditions of the EPS are as follows:  
1. The active power generated by the isolated system is 2975 MW of which 750 MW are from wind farm generation;
2. The isolated system's total active capacity incl. HVDC is 4025 MW. Importing power is 1250 MW, exporting power is 200 MW in the course of electricity trading through HVDC connections with neighboring EPS;  
Figure 1: Scheme of the isolated electric power system. 3. The 330 kV voltage is controlled by shunt reactors (SHR). A highly effective way to control the voltage and increase the inertia of the system is to put hydro-generators into operation, which can operate in synchronous compensator mode. The units capable of operating in synchronous condenser (SC) mode: one each for EPS parts No.2 and No.3. 4. The isolated EPS is divided into three parts, which can also operate independently;
5. The isolated EPS is connected to neighboring EPSs via eleven OHLs and four HVDCs;
6. One of the HVDCs is of the BtB type;
7. The critical frequency value of the isolated EPS is 49.20 Hz, at which the UFLS is triggered;
8. The generators are operating with continuously activated FCR function: EPS No.1 and EPS No.2;  
Isolated EPS normal voltage level 350-360 kV. The frequency stability of the electric power system is closely related to the rotor angle stability.