%0 Journal Article
%T Interrupting Short-Circuit Direct Current Using an AC Circuit Breaker in Series with a Reactor
%A Saurabh Kulkarni
%A Surya Santoso
%J Advances in Power Electronics
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/805958
%X This paper describes and demonstrates the principle and efficacy of a novel direct current fault interruption scheme using a reactor in series with a controlled rectifier and a conventional AC circuit breaker. The presence of the series reactor limits the capacitive discharge current from the DC filter capacitor at the output terminals of the phase-controlled rectifier. In addition, the series reactor along with the filter capacitor forms an underdamped series RLC circuit which forces the fault current to oscillate about zero. This synthetic alternating current can then be interrupted using a conventional AC circuit breaker. The selection criteria for the series reactor and overcurrent protection are presented as well. Using the proposed scheme for an example case, a DC fault current magnitude is reduced from 56£¿kA to 14£¿kA, while the interruption time is reduced from 44£¿ms to 25£¿ms. 1. Introduction Medium voltage DC or MVDC system architectures are being considered in distribution systems of electric ships as well as electric vehicles [1, 2]. Such systems are generally fed by phase-controlled rectifiers or simply controlled rectifiers. They are constructed using thyristors as the switch element in the bridge. The firing pulses of the thyristors can be controlled to change the DC voltage at the output terminals of the rectifier. However, a fault at the terminals of a controlled rectifier results in a large magnitude fault current. Without current zero crossings, clearing such faults is challenging. Furthermore, for faults with low fault resistance (or even bolted faults) the transient DC fault current has a high magnitude impulse component with a very short rise time. This can have detrimental effects on the equipment. Existing and proposed techniques for interrupting DC fault current utilize electromechanical interrupters, solid-state switches, and combinations of both technologies [2, 3]. In order to utilize electromechanical circuit breakers (EMCBs) in DC systems, it is proposed to generate artificial current zeros in the arc by superimposing a counter flow of current, typically from an oscillating circuit evoked only during circuit breaking. On the other hand, solid-state circuit breakers (SSCBs) make use of power electronic switches for interrupting the current without arcing [4¨C6]. Disadvantages of SSCBs include the absence of galvanic isolation and generally lack of the same withstand against transient overvoltages. Power semiconductor switches have high conduction losses due to on-state resistance and forward voltage drop discouraging their use.
%U http://www.hindawi.com/journals/ape/2012/805958/