Technical Presentations

Insulation coordination study of 220 kV transmission line for reliability improvement against lightning-induced overvoltages877

Abstract
This presentation shows a detailed insulation coordination verification using EMTP. It includes an accurate representation of transmission line components considering actual site data such as conducto... see morer arrangement, line length, line parameters, insulator details, tower structure and location, tower grounding resistance, and lightning data.

Tag(s): Insulation Coordination, Lightning Strike, LIOV, Line Surge Arresters, Back-Flashover

LEMP and Ground Conductivity impact on the Direct Lightning Performance of a Medium-Voltage Line879

Abstract
As part of this presentation, calculations of direct lightning overvoltages are analyzed in a medium-voltage line of such type, equipped with a multi-point grounded shield wire over lossy soil, taking... see more into account the effects of electromagnetic pulses (LEMPs), which are generally ignored when direct strokes are studied.

Tag(s): Lightning Electromagnetic Pulse, Ground Conditivity, Shielding Failure, Back-Flashover, LIOV

Response of Overhead Lines to Direct Lightning Strikes: Assessment of the LEMP Effects852

Abstract
In the usual practice, the evaluation of the overvoltages due to direct lightning strikes to overhead power line conductors is focused on the representation of the effects of the lightning current inj... see moreection, whilst the effects of the coupling between the conductors and the lightning electromagnetic pulse (LEMP) is disregarded. Motivated by recent results obtained for the case of a medium voltage line configuration with a shield wire, this extends the analysis to assess the contribution of the LEMP on the lightning performance of an overhead distribution with and without periodically grounded wires and surge arresters. Moreover, the presentation deals with the LEMP effect on the occurrence probability of flashovers on different phases, which is an important information on the service continuity of networks with isolated or compensated neutral earthing. A validation of the results is obtained by comparing the overvoltages calculated by using EMTP, together with the LIOV library for the LEMP calculation, and those obtained by a three-dimensional finite difference time-domain approach.

Tag(s): lightning, pulse, LIOV, surge, arrester

Insulation Coordination Study of 765kV GIS SUBSTATION788

Abstract
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 technol... see moreogy, 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.