We are happy to announce that we have completed an Insulation Co-ordination study for 220/33kV for one of the Reliance group of companies in Maharashtra using PSCAD software.
The scope of the project is to perform
1. Temporary over voltage study
2. Fast front over voltage study
3. Transformer Energization Study
The Project Consists Of
🔸220 kV GIS with two incomer line.
🔸Two nos. of 220 / 33 kV, 25/31.5 MVA Power transformer.
Temporary Overvoltage Study
In Temporary Overvoltage study, the following cases are simulated and analysed.
i) Ferranti effect
ii) Load rejection
iii) Fault (LG & LLG) with Load rejection
iv) Fault (LG, LLG)
From the analysis, it can be concluded that the continuous overvoltage measured in the network during Ferranti effect case is less than the maximum continuous operating voltage of Outdoor and GIS surge arrester.
The maximum voltage at 220kV GIS is 197.50kV (For a LLG fault at 220kV GIS bus) which is less than the TOV capability of surge arrestor. From the study, it is concluded that the surge arrester will not operate in temporary over voltage circumstances.
Fast Front Overvoltage Study
For Fast Front Overvoltage study, Direct stroke & Back flashover on the 220 kV line cases are simulated and analysed.
Based on Direct lightning and Back flashover studies performed, surge arrestor are enough to protect all the equipment’s at the 220 kV GIS. Maximum raise in voltage for the longest path has protection margin of 1.85 and shortest path has protection margin of 1.84 against the required protection margin of 1.2.
From the Insulation co-ordination study, it is observed that Lightning arrester at outdoor GIS, surge arrester at indoor GIS and arrester near Power transformer HV side is needed to protect all the equipment at the 220kV GIS substation.
Transformer Energization Study
For Transformer energization study, the following cases are simulated and analysed.
i) Energizing transformer with Maximum Grid Short Circuit Current & with residual flux
ii) Energizing transformer with Maximum Grid Short Circuit Current & without residual flux
iii) Energizing transformer with Minimum Grid Short Circuit Current & with residual flux
iv) Energizing transformer with Minimum Grid Short Circuit Current & without residual flux
During the Energizing of transformer, the inrush current is 1.014kA peak. The maximum voltage dip observed during the Energization of 25/31.5 MVA, 220/33 kV transformer is 4.26% which is well within the limits as per Working Group C4.307.
Congratulations to Selvakumar and Ajith G for bagging the project, and Congratulations to Kishore for the successful execution of the project.
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