KNR has done over 20 assignments of insulation coordination study for gas insulated substations up to 400kV for national and overseas clients.
Using EMTP package EMTP-RV from Powersys, insulation co-ordination study for lightning and switching over voltage performance is being carried out adopting the following methodology.
Steps involved are summarized below:
Step 1: Select most onerous path configuration of the system for the study.
Step 2: Collect, compile and validate data as per data questionnaire.
Step 3: Model the components of the system - Power Transformer, GIS section - OHL section, Surge arresters, cable, etc. & Develop network diagrams for the modeled system for EMTP analysis.
Step 4: Study the specific requirements with respect to operational philosophy and practice and select Lightning current stroke peak and shape for carrying out Lightning impulse overvoltage performance under shielding failure and BFO conditions.
Step 5: Decide the number of cases to be studied for Insulation Coordination exercise.
Step 6: Run EMTP-RV analysis with MicroTran version 3.25 to assess voltage stresses at surge impedance transition boundaries.
Step 7: If the nominal system voltage is above 300kV, carryout SOV studies for various conditions to validate the Insulation Coordination achieved based on LIOV performance.
Step 8: Study the Alternatives of the configuration satisfying Insulation Coordination protective ratios and choose the best.
Step 9: Construct the waveforms of the voltage stresses at surge impedance transition boundaries for the conditions studied.
Step 10: Study the controlling effect required and location to select type and characteristics of the surge arresters & specify the class and energy capacity required.