H. Radmanesh, M. Rostami,
Volume 7, Issue 4 (12-2011)
Abstract
this work studies the effect of neutral earth resistance on the controlling ferroresonance oscillation in the power transformer including MOV surge arrester. A simple case of ferroresonance circuit in a three phase transformer is used to show this phenomenon and the three-phase transformer core structures including nonlinear core losses are discussed. The effect of MOV surge arrester and neutral earth resistance on the onset of chaotic ferroresonance and controlling chaotic transient in a power transformer including nonlinear core losses has been studied. It is expected that these resistances generally cause into ferroresonance control. Simulation has been done on a power transformer rated 50 MVA, 635.1 kV with one open phase. The magnetization characteristic of the transformer is modelled by a single-value two-term polynomial with q=7, 11. The core losses are modelled by third order in terms of voltage. The simulation results reveal that connecting the MOV arrester and neutral resistance to the transformer, exhibits a great impact on ferroresonance over voltages.
Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved.
F. Amanifard, N. Ramezani,
Volume 12, Issue 3 (9-2016)
Abstract
The article presents the transients analysis of the substation grounding systems and transmission line tower footing resistances which can affect to the back-flashover (BF) or overvoltage across insulator chain in an HV power systems by using EMTP-RV software. The related transient modeling of the grounding systems is based on a transmission line (TL) model with considering the soil ionization. In addition, different configuration of grounding system have been simulated to calculated the BF, including number of vertical grounding rod, length of rod, point of lightning current injection into the grounding grid and using two depth design of grounding system where the surface of substation under consideration is very small orit is necessary to bury the grounding grid in the rocky media, occasionally. The simulation results have shown that how the mentioned parameters can considerably affect inception of BF, and suitable design of grounding system can reduce damages caused by lightning.
