Contents lists available at ScienceDirect Electric Power Systems Research journal homepage: www.elsevier.com/locate/epsr Comparative research into transients by switching of high voltage shunt reactor Srećko Bojić a, ⁎ , Boris Babić a , Ivo Uglešić b a Energy Institute Inc., HR-10000 Zagreb, Croatia b University of Zagreb, Faculty of Electrical Engineering and Computing, HR-10000 Zagreb, Croatia ARTICLE INFO Keywords: Controlled switching Shunt reactor Circuit breaker Arc-reignition Inrush current EMTP-ATP ABSTRACT This article deals with results of performed studies of transient phenomena in application of controlled switching technique by switching high voltage 123 kV, 100 MVAr shunt reactor. First, for switching a single-pole hy- draulically operated SF 6 circuit breaker has been selected and after that, one with electric motor-drive. In preparing of experimental part of studies the EMTP-ATP software has been used in computer simulations, further for analyses the cases of optimal controlled switching and switching within time deviation limits. For simulation of uncontrolled switching with current chopping and arc-reignition dynamic model of arc behavior has been implemented. The field tests with both circuit breakers have been repeated in similar network conditions for further statistical analyses. During some tests, the transient phenomena of uncontrolled switching have been observed. The achieved experimental results were compared with the computer simulations. 1. Introduction Transients phenomena by switching-off a high voltage (HV) shunt reactor in general terms are the well known problem [1,2,4]. In the overvoltage domain they are connected with the breaking of small in- ductive currents, related to the switching devices, to his mechanics and type of extinguishing media [1–4]. When current chopping or arc reignition or both phenomena have occurred, they usually lead to sig- nificant switching overvoltages. Contrary, during the process of switching-on, very high inrush currents as the transients can be ob- served if the moment of switching is not optimal. Because of that they can be potentially very stressful for insulation and mechanical system of shunt reactor as well for other equipment [5]. Therefore they have to be prevented or mitigated. As an effective measure in prevention of such transients the controlled switching technique is in use [6,7]. Ad- ditionally, for overvoltage protection of insulation system, metal oxide (MO) arresters are generally used [8]. This article deals with and compares the part of results of performed transient phenomena studies by switching of HV 123 kV, 100 MVAr shunt reactor with two different types of SF 6 circuit breaker (CB) in one 400/110 kV substation, first with single-pole hydraulically operated (CB1) [9], and second one with electric motor-drive system (CB2), the both equipped with the proper switching controller. 2. Case studies description First, for switching of HV shunt reactor a single-pole hydraulically operated CB has been installed. After installation, very soon some problems with instability of its mechanics have been observed resulting in the periodical incapability for switching of shunt reactor. For illus- tration, Fig. 1 shows the typical recorded “closing” and “opening” time of CB during some field tests. Fig. 2 depicts much more details of re- corded long term deviation in the switch-time operation of the CB1, and also shows the periods of incapability for switching [9]. It was pretty clear that this time deviation in CB mechanics, more than ± 2 ms, can lead to serious cases of uncontrolled switching in despite of implemented CB controller with adaptive feedback. Therefore, the hydraulically operated CB1 has been replaced with the new one (CB2) with electric motor-drive system in order to provide much more reliable controlled switching. Prior to replacement, first experimental study (case I) of transients has been performed, in order to collect and compare the real measured data before and after the re- placement. The switching of shunt reactor has been carried out in controlled and uncontrolled conditions, within different time margins. Some of the first collected data were analyzed and compared to the results of performed EMTP/ATP computer simulation and were pre- sented in Ref. [9]. In several cases of shunt reactor switching-off the arc-reignition has been recorded with significant transient phenomena. Also, by switching-on in time out of optimal margins for controlled https://doi.org/10.1016/j.epsr.2018.04.018 Received 8 December 2017; Received in revised form 23 April 2018; Accepted 25 April 2018 ⁎ Corresponding author. E-mail address: srecko.bojic@ie-zagreb.hr (S. Bojić). Electric Power Systems Research 162 (2018) 74–82 0378-7796/ © 2018 Elsevier B.V. All rights reserved. T