International Journal of Advanced Engineering, Management and Science (IJAEMS) [Vol-6, Issue-1, Jan-2020] https://dx.doi.org/10.22161/ijaems.61.10 ISSN: 2454-1311 www.ijaems.com Page | 56 Study the Line Length Impact on the Effective of Overvoltage Protection in the Low Voltage Network Ly Thi Ngoc Chi 3 , Bui Thi Mong Nhi 2 , Anh Q H 1 , Nghia LT 1 1 HCMC University of Technology and Education Email: anhqh@hcmute.edu.vn; trongnghia@hcmute.edu.vn 2 Thu Duc College of Economy and Technology Email: nhibuithimong@gmail.com 3 Cao Thang Technical College Email: lythingocchi@caothang.edu.vn Abstract—The overvoltage protection devices on low-voltage power lines (SPD) are often made using GDA and MOV technology. The selection, proper use and installation of overvoltage protective devices, taking into account the effect of line length and the types of combinations that will affect the protection efficiency, is essential. This paper builds GDA and MOV models with high similarities to the prototype. The evaluation of protection efficiency with different types of coordination and the effect of line length was investigated by simulation-modeling method in simulink environment of Matlab software. Keywords— GDA (Gas Discharge Arrester), MOV (Metal Oxide Varistor), SPD (Surge Protective Device), Protection Efficiency, Simulink, Matlab. I. INTRODUCTION Previous studies have focused on surge protection on low- voltage power lines for equipment with the assumption that lightning impulses directly affect the protective equipment [1, 2]. However, in practice it is necessary to combine protective devices manufactured under MOV technology [3], and the line with characteristics containing capacitance and inductance acting as a surge reduction filter. Therefore, it is necessary to study the impact of line length on the protection efficiency of the overvoltage protection in the low voltage distribution network under the condition of combining the installation of SPD using MOV technology and GDA technology. The results of the research were tested by the simulation modeling method in Simulink/Matlab environment. II. GDA MODEL 2.1. Electric Arc Equation between two Electrodes The GDA model that takes into account the arc appearing between the two electrodes is built as a mathematical model, describing the electrical properties of the arc. This type of model does not simulate complex physical processes within a circuit breaker, but describes the behavioral voltage of GDA. Measurement of voltage and current signals is used to extract differential parameters for differential equations that describe the non-linear resistance of the electric arc for specific measurements. According to Mayr, the differential equation describing the arc phenomenon between the electrodes of GDA is presented by the expression (1) [4, 5, 6, 7]. (1) 2 2 (1) (1) (2) (1) ln (2) 1 1 (1) x x dx u e u d g u gu dt P dt P y e u i gu                     (1) Where: x (1) is the state variable of the differential equation, and is the natural logarithm of the arc conductivity ln(g); x (0) is the initial value of the state variable, which is, the initial value of the arc conductivity: g(0); u (1) is the first input variable of the DEE block, this is the arc voltage u; u (2) is the second input variable of the DEE block, representing the circuit breaking of circuit breaker: u (2) = 0 when the contacts of the circuit breaker are closed and u (2) = 1 when the contacts of the circuit breaker are open.; y is the output variable of the DEE block, this is the arc current i; g is the conductance of the arc; u is the arc voltage; i is the arc current; τ is the arc constant of time; P is the cooling energy. 2.2. GDA model The breakdown voltage is the parameter of the control switch SC (Switch Control). When the voltage applied to the GDA (on the switch K) reaches the value of the breakdown voltage, a time delay is calculated according to