The scope of the project is to perform
1. Temporary over voltage study
2. Slow front over voltage study
3. Fast front over voltage study
The site is located 100 km northeast of Riyadh City Saudi Arabia. Saad Solar PV Park is a 300MW ground-mounted solar PV power project. The project is expected to generate 876,000MWh of electricity annually.
The Project Consists Of
A 132kV double circuit feeder is connected to the 380/132kV BSP Gas Insulated Switchgear (GIS) located at the 380kV GIS building. The 132kV GIS is connected to the 33kV AIS switchgear at the SAAD substation via the 33/132kV Power Transformers. The terminal voltage of the SAAD solar PV plant is 33kV.
Temporary Overvoltage Study
In the Temporary Overvoltage study, the following cases are simulated and analysed.
i) Ferranti effect
ii) LG & LLG fault at 132kV OHL receiving terminal
iii) LG & LLG fault at 33kV switchgear
iv) LG & LLG fault at longest collector feeder
• The continuous overvoltage observed at 132 kV OHL receiving terminal is 83.718kV during the Ferranti effect which is less than the maximum continuous operating voltage (92kV) of the surge arrester. Hence, the selected surge arrester at 132kV level is suitable for the system.
• An LG & LLG fault applied at 132kV OHL receiving terminal. The maximum voltage observed is 81.946kV which is less than the TOV rating (132kV) of the surge arrestor. An LG & LLG fault applied at 33kV AIS switchgear. The maximum voltage observed is 36.015kV which is higher than the TOV rating (34.5kV) of the surge arrestor.
• An LG & LLG fault applied at 33kV longest collector feeder. The maximum voltage observed is 35.968kV which is higher than the TOV rating (34.5kV) of the surge arrestor.
From the analysis at the 33kV level, it is concluded that the selected surge arrester is not suitable in temporary over-voltage circumstances. It is recommended to select a surge arrester rating to the rated voltage (Ur) of 36kV and continuous operating voltage (Uc) of 28.8kV.
Switching Overvoltage Study
In the Switching Overvoltage study, the following cases are simulated and analysed.
i) 132kV transmission line energization
ii) 160MVA, 132/33 kV transformer energization
iii) 33kV capacitor bank switching
iv) 33kV cable energization
• The maximum overvoltage observed during the energization of the 132kV transmission line is 124.379 kVpeak which is less than the BIL rating 650 kVpeak of 132 kV AIS.
• The maximum overvoltage observed during the energization of 160 MVA, 132/33 kV transformer is 118.448 kVpeak which is less than the BIL rating 650 kVpeak of 132 kV AIS.
• The maximum overvoltage observed during the switching of the 33kV capacitor bank is 45.478 kVpeak which is less than the BIL rating 170 kVpeak of 33 kV AIS.
• The maximum overvoltage observed during the energization of the 33kV cable is 62.254 kVpeak which is less than the BIL rating 170 kVpeak of 33 kV AIS.
From the analysis, it can be concluded that the maximum overvoltage measured in the network is within the insulation level of the equipment in the substation.
Fast Front Overvoltage Study
i) Direct Stroke – 132 kV transmission line
ii) Back Flashover – 132 kV transmission line
Based on direct lightning and back flashover studies, a class 2 surge arrester is enough to protect all the equipment at the 132 kV AIS. The maximum raise in voltage for the longest path has a protection margin of 2.025692.
From the Insulation coordination study, it is observed that the Lightning arrester at OHL and the power transformer HV side are sufficient to protect all the equipment at the 132/33kV AIS substation.
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