## 5 Semiconductor Breakers and Operation Principle of the Proposed Method  
Different types of Mechanical Circuit Breakers (MCB) and short-circuit termination strategies have been implemented for DC fault-protection purposes. Whereas, due to the rapid increase of DC fault currents and a low operation speed (hundreds of ms) of MCBs, it requires distribution line and associated power electronics devices with higher capacity and size to sustain such a high current. Comparatively, SSCB-based protection methods can provide high-speed protection (few us) schemes to prevent the high initial cost and occupation of large spaces [29]. The SSCBs are embedded into two useful major categories in protection system devices: (i) semiconductor current limiters, and (ii) semiconductor breakers [30]. The SSCBs consist of semiconductor switches (IGBT, MOSFET, etc.). Due to the absence of moving mechanical parts, the SSCB has a longer lifespan than MCB [31]. Among different types of semiconductor switches, the IGBT is a good choice for low-voltage protection purposes because of its operation speed, ruggedness, commercial availability, and low power requirement to run the gate drive. For reliability, the different circuit needs to be combined with SSCB, which are mentioned as follows:  
* Resistor, Capacitor, and Diode (RCD) Snubber Circuit: The main components of the RCD circuit are the resistor, capacitor, and diode. The resistor is connected in series to prevent high inrush current while the breaker is connecting, and the shunt capacitor suppresses the voltage jump during the disconnection of SSCB. Additionally, the anti-parallel diode circuit bypasses the high transient current, which generates when the breaker interrupts the circuit;
* Metal Oxide Variator (MOV): The MOV has the sustainability of frequent huge ripple currents and temporary high energy. Also, because of the variable resistance characteristics of MOV, it is used to protect electrical circuits under a surge voltage situation. The MOV makes a short circuit in high voltage conditions and its resistance is increased when the voltage decreases, meaning that the current-dependent equipment of the system will remain safe from the sudden voltage surge;
* Freewheeling Diode: Normally, the snubber diode is not an overvoltage protective device, but helps to prevent circuit damage by providing an emergency path for high energy of the stray components when an abrupt voltage spike is happening in an electrical circuit by a sudden change of supply current or fault conditions. Due to the capability of obtaining fast-fault interruption, SSCB can meet protection requirements for the DC-microgrid. A DC system has a unique challenge like DC short-circuit identification,appropriate grounding systems, and current limiting challenges. Due to a divergence in DC short-circuit current values, traditional protection devices will face challenges in reactivity and operating speed. Therefore, developing an appropriate protection strategy is quite important to expand the DC electrical system. In this study, line-to-ground faults (\(F_{1}\), \(F_{2}\), and \(F_{3}\)) were applied to evaluate the operation of the proposed protection system. Furthermore, the proposed protection system worked based on the current-rise technique of the fault current. For specification and detection of the fault situations, we defined the a threshold current in this strategy to identify the fault area easily. As shown in Figure 5, during the normal condition of the DC microgrid, the output of the control system for the circuit breaker was one and the circuit was prolonged to its normal operation. As soon as the control system sensed a divergence in the current of the circuit, the output signal changed to zero and the circuit breaker was disconnected to separate the faulted branch. Additionally, during the operation of SSCB, because of the abrupt interruption of the fault current, a large over-voltage would occur.