Energy and Power Engineering, 2013, 5, 225-235 http://dx.doi.org/10.4236/epe.2013.53022 Published Online May 2013 (http://www.scirp.org/journal/epe) Influence of dc Component during Inadvertent Operation of the High Voltage Generator Circuit Breaker during Mis-Synchronization Kadri Kadriu 1,2 , Ali Gashi 2 , Ibrahim Gashi 1,2 , Ali Hamiti 2 , Gazmend Kabashi 1,2 1 KOSTT—Kosovo Transmission System and Market Operator, Prishtina, Kosovo 2 Faculty of Electric Engineering and Computer Sciences, University of Prishtina, Prishtina, Kosovo Email: kadri.kadriu@kostt.com Received January 22, 2013; revised February 24, 2013; accepted March 8, 2013 Copyright © 2013 Kadri Kadriu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT This paper analyses the synchronization problem of a generator onto power system without satisfying synchronization condition. The main focus of the paper is on the impact of the dc component of the current in the high voltage circuit breaker during its close-open operating cycle. Using real time measurements of currents/voltages and angles during the close-opening cycle of high voltage generator circuit breaker and the impact of the dc component of current in context of interrupting large magnitude of current from the circuit breaker. In addition, the paper describes a study case model and the results of simulations performed using the software EMTP-ATP of an actual incident that occurred during the inadvertent synchronization of a large 339 MW, 24 kV generator to the grid. Keywords: High Voltage Generator Circuit Breaker; dc Component of Current; Asynchronous Connection; Delay Current Zero 1. Introduction The synchronising of large generators into power sys- tems results in electrical and mechanical transient proc- esses such as voltage, rotor angle, frequency and torque. These electromechanical transient processes, cause an extreme oscillation between generator and-power sys- tems, during an out-of-step condition which impose very high electromechanical stress on the generator. According to the operations experience, the tolerances of those parameters between generator and power system have to be strictly satisfied in order that the process of synchronization can be carried out without excessively high stress. During synchronization of the generator, it can happen that the generator could be connected to the network without meeting all of the synchronization conditions. This can happen for several reasons such a fault in the control systems, errors in synchronizing apparatus, de- fects of control cables, and human error. This paper de- scribes the response of electromechanical quantities dur- ing synchronization of generator to the power system (asynchronous mode). The main focus of the paper is on the impact of the dc component of the current in the high voltage circuit breaker during its close-open operating cycle. The analyses of problem is based on real time measurements of quantities currents/voltages and angles during the close-opening cycle of high voltage generator circuit breaker and the impact of the dc component of current in context of interrupting large magnitude of cur- rent from circuit breaker. In addition, the paper describes a study case model and the results of simulations per- formed using the software EMTP-ATP of an actual inci- dent that occurred during the inadvertent synchronization of a large 339 MW, 24 kV generator to the grid in which the synchronizing conditions were not met. The time elapsed from asynchronous connection mode until the opening of the circuit breaker, is 150 ms. Prior to connection with the power system, the generator was operating under no-load conditions and waiting to meet the synchronisation condition. As a consequence, due to this asynchronous connection and the wide voltage an- gles between the generator and the power system, ex- tremely high transient currents comparable to fault cur- rents occurred. Under those circumstances, the protection relays in the generator and in the connecting circuit de- tect high magnitude transient currents and send a tripping Copyright © 2013 SciRes. EPE