# Application of Surge Arrester in Limiting Voltage Stress at Direct Current Breaker
## 1 Introduction
Despite the simple and control-free structure (with only diodes and capacitors), the proposed breaker is only effective in reducing the arc across the mechanical switches when it is placed close to the source, where the upstream path impedance is negligible. When the proposed DCCB is used in the DC power line, the upstream-line parasitic inductance prevents the backflow of the fault current to the source, causing a voltage rise at the DC breaker's input terminals and a delay in the operation of the redirecting diodes. Surge protection devices (SPDs) [12; 13; 14; 15; 16; 17], also known as surge arresters, are widely used in power systems to mitigate and absorb fault energies caused by transients, such as switching, lightning, and temporary overvoltage. Surge arresters are typically comprised of cylindrical variable resistors with various diameters and heights that are made of composites with non-linear voltage-current characteristics. These composites are made in grains with smaller interior resistivity than exterior resistivity. The nonlinear voltage-current characteristic is due to the phenomenon occurring mainly on the boundary of the grains [15]. Under low voltage across the surge arrester, voltage-current characteristics follow Ohm's law. As the voltage goes beyond the surge arrester's limit, the voltage-current characteristic becomes highly non-linear and the current increases sharply. Various reports [18; 19] \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \begin{tabular}{c} **Solid-State** \\ **Circuit Breaker** \\ \end{tabular} & \
\begin{tabular}{c} **Mechanical** \\ **Circuit Breaker** \\ \end{tabular} &
\begin{tabular}{c} **Hybrid** \\ **Circuit Breaker** \\ \end{tabular} \\ \hline \multirow{2}{*}{**Response time**} & Very fast & Slow & Fast \\  & (A few microseconds) & (Tens of milliseconds) & (A few milliseconds) \\ \hline \multirow{2}{*}{**Cost**} & High & Low & Very high \\ \hline \multirow{2}{*}{**Size**} & Compact & Large & Large \\ \hline \multirow{2}{*}{**Loss**} & Very high & Very low & Very low \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of different DCCB models [11]. highlight the application of the surge arresters in mitigating high voltages (500 kV), particularly in transient arcs over the insulators. The authors of [20] introduced a novel zonal fault-detection scheme for DC wind farms that leverages the strategic disposition of surge arresters in multipurpose grounding systems. Surge arresters have been used in mechanical and hybrid DCCBs to absorb the fault energy after it is redirected to bypassing circuits that comprise inductors or solid-state switches such as IGBTs or thyristors [21]. In this paper, a modification to the hybrid DCCB introduced in [11] is proposed, utilizing surge arresters, so that the breaker can be used anywhere along the DC power line and alleviate the shortcoming of the original hybrid DCCB proposed in [11]. In this work, the surge arrester plays two important roles, namely up-/downstream fault energy absorption and providing a reverse voltage for faster current decay in part of the fault disruption period. High-current hardware tests (900 A) are performed to address practical issues pertaining to high-current disruption under voltages under 500 V. The hybrid DCCB mathematical model is also discussed, and detailed simulation studies are performed. For low-voltage applications, this paper proposes a modified bipolar hybrid DC breaker based on the authors' previous work [11; 22], which is applicable to high-voltage DC line/load inductances, by using surge arresters. The proposed DC breaker can potentially be used at higher voltage levels such as in medium-voltage applications. The following is the organization of the rest of the paper: Section 2 proposes the hybrid DCCB mechanism. Section 3 presents the mathematical model. Section 4 includes the experimental results. Section 5 presents the conclusion and perspectives for future research. Figure 1: (a) Proposed DCCB design; (b) DC system circuit diagram.