Figure 10.6.5-7 Power Flow Diagram (Thermal Maximum Night Peak in 2025, Generating Operation, Connected to Kotmale and New Polpitiya,Loggal Unit Capacity 200MW)
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Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report Loggal PSPP (Source: JICA Study Team) Figure 10.6.5-7 Power Flow Diagram (Thermal Maximum Night Peak in 2025, Generating Operation, Connected to Kotmale and New Polpitiya,Loggal Unit Capacity 200MW) Electric Power Development Co., Ltd. 10-165 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report Loggal PSPP (Source: JICA Study Team) Figure 10.6.5-8 Power Flow Diagram (Thermal Maximum Night Peak in 2025, Generating Operation, Connected to Kotmale and New Polpitiya, Loggal Unit Capacity 150MW) Electric Power Development Co., Ltd. 10-167 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report Loggal PSPP (Source: JICA Study Team) Figure 10.6.5-9 Power Flow Diagram (Off Peak in 2025, Pumping Operation, Connected to Kotmale,Loggal Unit Capacity 200MW) Electric Power Development Co., Ltd. 10-169 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report Loggal PSPP (Source: JICA Study Team) Figure 10.6.5-10 Power Flow Diagram (Off Peak in 2025, Pumping Operation, Connected to Kotmale,Loggal Unit Capacity 150MW) Electric Power Development Co., Ltd. 10-171 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report Loggal PSPP (Source: JICA Study Team) Figure 10.6.5-11 Power Flow Diagram (Off Peak in 2025, Pumping Operation, Connected to Kotmale and New Polpitiya, Loggal Unit Capacity 200MW) Electric Power Development Co., Ltd. 10-173 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report Loggal PSPP (Source: JICA Study Team) Figure 10.6.5-12 Power Flow Diagram (Off Peak in 2025, Pumping Operation, Connected to Kotmale and New Polpitiya, Loggal Unit Capacity 150MW) Electric Power Development Co., Ltd. 10-175 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report (2) Short Circuit Current Analysis The three phase fault current analyses at bus conductors of Loggal PSPP, Kotmale P/S, and New Polpitiya are carried out for Hydro Maximum Night Peak cases and Thermal Maximum Night Peak cases, as the most severe loading cases. As shown in Table 10.6.5-1, it is confirmed that the currents satisfies the criteria for all cases. Table 10.6.5-1 The Three Phase Short Circuit Currents (in 2025) Loading Unit Capacity of T/L P/S, S/S Current Scenario PSPP Kotmale 220kV 25.3kA 200MW Loggal 220kV 9.2kA To Kotmale P/S Kotmale 220kV 25.3kA 150MW Loggal 220kV 9.1kA Hydro Kotmale 220kV 24.0kA Maximum 200MW Loggal 220kV 18.7kA Night Peak New Polpitiya 220kV 20.1kA PI Connection Kotmale 220kV 23.9kA 150MW Loggal 220kV 18.4kA New Polpitiya 220kV 20.0kA Kotmale 220kV 21.3kA 200MW Loggal 220kV 8.8kA To Kotmale P/S Kotmale 220kV 21.2kA 150MW Loggal 220kV 8.7kA Termal Kotmale 220kV 20.7kA Maximum 200MW Loggal 220kV 17.8kA Night Peak New Polpitiya 220kV 18.2kA PI Connection Kotmale 220kV 20.6kA 150MW Loggal 220kV 17.5kA New Polpitiya 220kV 18.1kA (Source: JICA Study Team) (3) Transient Stability Analysis 1) Three phase line fault at Loggal PSPP In case that T/L from Loggal PSPP is connected to T/L between Kotmale P/S and New Polpitiya S/S with PI connection, it is set that three phase line fault occurs at a point in T/L shown below since the power flow is heavier than the other sections. Peak: Loggal- New Polpitiya, Off-peak: Loggal- Kotmale The results of transient stability analysis of three phase line fault are shown in Figure 10.6.5-13 to Figure 10.6.5-24. The results in cases for pumping operation (Figure 10.6.5-21, Figure 10.6.5-22) show that the network becomes unstable and steps out occurs in case that Loggal PSPP is connected to Kotmale P/S. The cause is assumed that length of T/L is longer than that of Maha PSPP to Kotmale P/S and from Halgran PSPP to Kotmale P/S. In order to keep Power system stable, the conductor of the transmission line from Loggal PSPP to Kotmale should be reconsidered so that Electric Power Development Co., Ltd. 10-177 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report the impedance of T/L can be reduced. The other results of transient stability analysis show that network can be in stable. However, the weak damping phenomena are observed within around initial 10 seconds. From the results of these, it is suggested that the power system stabilizer is to be equipped with large size units to be developed in the future. 2) One Unit Tripping at Loggal PSPP a) Frequency drop followed by loss of generator The results of the dynamic simulation for one unit tripping Loggal PSPP are shown in Figure 10.6.5-25 to Figure 10.6.5-32. The results of the study show in all cases that the system frequency drops to 48.75Hz which is the criteria; the load shedding is taken place. In this regard, it is calculated that the system frequency dropping in Thermal maximum scenario is larger than that in Hydro maximum scenario. This is because there is difference of the number of power plants operated with free governor mode in Hydro Maximum cases (HMNP) and in Thermal Maximum cases (TMNP). HMNP: Samanalawewa, Bowathenna, Kotmale, Upper Kotmale, Victoria, Puttalam, Ambalangoda, Sampoor TMNP: Victoria, Kotmale, Kelanitissa Considered the above-mentioned calculation results, it is assumed that the mumber of power plants with governor free mode has considerable impact on the power system stability. Therefore, it is suggested that free governor operation system should be considered for relatively large plants to be constructed in the future. b) Frequency rise by loss of generator of pumping operation The results of the dynamic simulation for one unit tripping Loggal PSPP are shown in Figure 10.6.5-33 to Figure 10.6.5-36. The results show that in very case, the system frequency does not excess 51.5Hz which is the criteria; the alarm of thermal power plants occurs for the system frequency rise. In this regard, in the simulation, it is set that the coal power plants in the power grid (Puttalam, Ambalangoda, and Sampoor) are operated with free governor mode in the same manner as “a) Frequency drop followed by loss of generator”. Therefore, it is suggested that free governor operation system should be considered for relatively large plants to be constructed in the future. Electric Power Development Co., Ltd. 10-178 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report 60 50 40 30 20 10 Rotor Angle (deg) Angle Rotor 0 -10 0 5 10 15 20 25 30 Time (seconds) 300 250 200 150 100 50 Bus Voltage (kV) Bus Voltage 0 -50 0 5 10 15 20 25 30 Time (seconds) (Hydro Maximum Night Peak in 2025,Generating Operation, Connected to Kotmale, Loggal Unit Capacity 200MW) (Source: JICA Study Team) Figure 10.6.5-13 Three-phase Fault at Loggal end of Loggal-Kotmale 220kV Line-USR 60 50 40 30 20 10 Rotor Angle (deg) Angle Rotor 0 -10 0 5 10 15 20 25 30 Time (seconds) 300 250 200 150 100 50 Bus Voltage (kV) Bus Voltage 0 -50 0 5 10 15 20 25 30 Time (seconds) (Hydro Maximum Night Peak in 2025,Generating Operation, Connected to Kotmale, Loggal Unit Capacity 150MW) (Source: JICA Study Team) Figure 10.6.5-14 Three-phase Fault at Loggal end of Loggal-Kotmale 220kV Line-USR Electric Power Development Co., Ltd. 10-179 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report 60 50 40 30 20 10 Rotor Angle (deg) Angle Rotor 0 -10 0 5 10 15 20 25 30 Time (seconds) 300 200 100 0 Bus Voltage (kV) Bus Voltage 0 5 10 15 20 25 30 -100 Time (seconds) (Hydro Maximum Night Peak in 2025,Generating Operation, Connected to Kotmale and New Polpitiya, Loggal Unit Capacity 200MW) (Source: JICA Study Team) Figure 10.6.5-15 Three-phase Fault at Loggal end of Loggal-New Polpitiya 220kV Line-USR 300 200 100 0 0 5 10 15 20 25 30 Bus Voltage (kV) Bus Voltage -100 Time (seconds) 50 40 30 20 10 0 -10 0 5 10 15 20 25 30 Rotor Angle (deg) Angle Rotor -20 Time (seconds) (Hydro Maximum Night Peak in 2025,Generating Operation, Connected to Kotmale and New Polpitiya, Loggal Unit Capacity 150MW) (Source: JICA Study Team) Figure 10.6.5-16 Three-phase Fault at Loggal end of Loggal- New Polpitiya 220kV Line-USR Electric Power Development Co., Ltd. 10-180 Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka Final Report 50 40 30 20 10 0 Rotor Angle (deg) Angle Rotor -10 0 5 10 15 20 25 30 -20 Time (seconds) 300 250 200 150 100 50 Bus (kV) Volateg 0 -50 0 5 10 15 20 25 30 Time (seconds) (Thermal Maximum Night Peak in 2025,Generating Operation, Connected to Kotmale, Loggal Unit Capacity 200MW) (Source: JICA Study Team) Figure 10.6.5-17 Three-phase Fault at Loggal end of Loggal-Kotmale 220kV Line-USR 50 40 30 20 10 0 Rotor Angle (deg) Angle Rotor -10 0 5 10 15 20 25 30 -20 Time (seconds) 300 250 200 150 100 50 Bus (kV) Volateg 0 -50 0 5 10 15 20 25 30 Time (seconds) (Thermal Maximum Night Peak in 2025,Generating Operation, Connected to Kotmale, Loggal Unit Capacity 150MW) (Source: JICA Study Team) Figure 10.6.5-18 Three-phase Fault at Loggal end of Loggal-Kotmale 220kV Line-USR Electric Power Development Co., Ltd.