Author(s): Carlo Alberto Nucci & Fabio Tossani
Type:Technical Presentation
Date: 2021-09-07

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

Author(s): Aboutaleb Haddadi
Type:Technical Presentation
Date: 2021-09-02

Ground Fault Overvoltage with Inverter-Based Distributed Energy Resources841

Abstract
A Ground Fault Overvoltage (GFO) can occur in situations where an ungrounded transmission line and associated ungrounded transmission equipment is energized from distribution connected Distributed En... see moreergy Resource (DER) during a transmission single-phase-to-ground (SLG) fault. The condition could result in 1.73 pu overvoltage on phase to ground connected equipment which will be sustained until the DER ceases to energize the substation distribution transformer. Transmission equipment on the isolated circuit will be subjected to the above phase to ground overvoltage, also if there is frequency shift, the isolating transmission circuit breakers could potentially see up to 2.73 pu phase to ground overvoltage. Such an overvoltage can cause damage to customer or utility equipment and must be avoided. GFO concerns are already becoming a barrier to large-scale DER deployment either by posing low hosting capacity or by necessitating installation of costly mitigation equipment. Utilities need to study GFO risks and identify low-cost mitigation options to enable large-scale DER deployment. Given the fundamental differences in mechanisms and phenomena driving a GFO under DERs, classical GFO analysis methods do not apply to inverters, and advanced simulation methods and tools are required.


This presentation highlights EPRI’s work on GFO analysis, concerns, and evaluation of mitigation options using EMTP. The objective is to determine if or when high DER penetration presents a GFO problem and how to prioritize the mitigation and equipment evaluation. This includes evaluating the impact lightning arresters can have in reducing or clamping the overvoltage, the application and performance of high voltage substation overvoltage protection, and DER on-board voltage/frequency protection. The presentation further provides modeling recommendations for such a study using EMTP. As DER deployment increases, utilities will need to perform similar analysis to identify potential overvoltage risks and develop low-cost mitigation methods. This work provides a basis for such a study.

Tag(s): gfov, tov, ibr, DER, inverter, islanding, load rejection, inverter based resources

Author(s): N.K.Nathan - KNR Engineers
Type:Technical Presentation
Downloaded: 0
Date: 2021-06-17

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.

Author(s): Diego F. Rodríguez - GERS
Type:Technical Presentation
Date: 2021-06-17

TOV for renewable, evaluating three different grounding technologies783

Abstract
Temporary overvoltages (TOV) are oscillatory overvoltages mainly caused by switching or faults, which are of relatively long duration and undamped or slightly damped. Maximum overvoltages under faulte... see mored conditions can require considerable energy magnitudes absorbed by surge arresters.
These energies may overpass maximum limits and lead to equipment damage.

This project presented a study to identify the maximum TOV at the MV equipment of a PV power plant during fault-clearing events. Two methods of TOV suppression are evaluated, including grounding transformers and fast grounding switches under two different configuraions. An electrical model was elaborated in EMTP to perform the simulation of the transient overvoltage due to the un-balanced fault clearance, considering each inverter of the PV plant. The results show that considering no grounding technologies at the feeders, the energy absorption limit is overpassed in the islanded system.

Therefore, a fast grounding switch or a system with grounding technology at each feeder is needed in order to protect the substation equipment.

Author(s): Ilhan Kocar, Polytechnique Montréal
Type:Technical Presentation
Date: 2020-11-20

The validation of field measured switching overvoltages, inclusion of statistical prestrike and corona modeling750

Abstract
<h2 class="title">EMTP USA User Conference 2019 </h2> <p class="tagline"><b>The validation of field measured... see more switching overvoltages, inclusion of statistical prestrike and corona modeling</b></p> <p id="text-intro">This presentation is on the simulation of switching overvoltages on transmission lines with trapped charge, validation of EMTP line models, modeling of prestrike in statistical simulation studies and discussion of necessary simulation practices by means of validations with field tests. On transmission lines where switching surges are not mitigated with closing resistors and/or surge arresters, high-speed reclosing on a line with trapped charge will produce high overvoltages that have been measured above 3 pu. Careful simulations of these switching events using available Electromagnetic Transient (EMT) programs consistently produce significantly higher voltages than the measurements. It is demonstrated that the transient voltage waveforms can be reproduced very well using frequency-dependent line models, but the magnitude of the maximum overvoltage is significantly overestimated unless the effect of corona is considered. In principle, once a line model is validated, it is possible to proceed with statistical simulation phase to identify the worst-case overvoltage, which is of utmost importance for transmission line and substation related issues such as the evaluation of minimum approach distance and clearance practices. However, before proceeding with statistical simulation phase, it is also necessary to tune the prestrike model in EMTP. In this presentation, we also discuss how to benefit from field tests to fine tune the generic prestrike model in EMTP and then how to proceed with statistical simulation studies while taking corona into account in an efficient manner.</p>