Insulation Coordination Study of 765kV GIS SUBSTATION

EMTP Virtual User Conference 2020 - N.K.Nathan - KNR Engineers

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Gas Insulated Substations provide cost effective solution due to reduced land requirements particularly in metropolitan area where power demand is registering steep growth. With the use of GIS technology, it is required to assess the risk of failure due to overvoltage. The Insulation Coordination study forms a very important aspect in design stage. This presentation deals with the IC study carried out for a large – 765/400/220kV GIS substation in a SUPER THERMAL POWER STATION in UTTAR PRADESH. Due to the decreasing ratio of lightning impulse withstand voltage to the system voltage, the difference between LIOV and VFTO decreases and this factor calls for VFTO performance analysis for 765kV GIS as well. The discussion includes modeling of Extra High Voltage GIS, Temporary Overvoltage (TOV), Lightning Impulse Overvoltage (LIOV), Switching Overvoltage (SOV) and Very fast transient Overvoltage (VFTO) performance analysis on 765kV GIS substation. TOV typically caused by fault to ground, load rejections and energization of long lines are analyzed to decide the rating of the surge arrester. LIOV simulation studies are carried out for possible onerous paths including longer and short paths to decide the location of the arrester. SOV analysis deals with the overvoltage due to switching operations during line energization, re-energization and fault occurrence and clearance. The LIOV and SOV results have been validated with reference to protective levels prescribed. The VFTO analysis is performed with various GIS disconnector operations in accordance with the methodology and guidelines as per CIGRE WG D1.03-TB 519 and the results are validated with the limits specified. Keywords: Insulation Coordination, VFTO, EHV, GIS, 765kV, Protective ratio.

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