There are complex physical phenomena for the interpretation of a molded case circuit breaker (MCCB) in a distribution system. Most of the studies of MCCB interruption phenomena were conducted with numerical analysis and experiments. This traditional approach may help improve the performance of the MCCB itself, but it is difficult to find connectivity with other systems. In this paper, the circuit model is proposed and the interruption phenomenon of MCCB is analyzed. The interruption of the MCCB is divided into three sections to deal with physical phenomena occurring in each area. A simplified model is proposed considering the characteristics of each section. Based on this model, the circuit model is proposed. To implement the features of each section, the calculation of physical phenomena is carried out, and this is expressed in the circuit model with resistance and zener diode. Comparing the results of the simulation with the experimental results is as follows. For 7-plates (basic state), the error rate is −5.6% in section II and 16.8% in section III. For 1-plate, the error rate is 36.5% in section II and −17.0% in section III. This case shows much difference from the simplified model in this paper, resulting in the largest error rate. The 7-plates and 5-plates cases, which are available in the general MCCB owing to the shortest distance from the arc, represent a relatively small error rate. Using the proposed circuit model, it is expected that the entire system, including the interruption phenomenon, can be interpreted as a single circuit model.

The low-voltage circuit breakers are widely used to protect loads in the distribution system. Interruption reliability of circuit breakers is important because they are a protective device close to the customer. In particular, the re-ignition phenomenon leads to over-current blocking failure due to the arc re-formed between electrodes despite the normal trip of the circuit breaker. In this paper, in order to improve the interruption performance against re-ignition, the dielectric recovery voltage measurement system of the circuit breaker is used and the experiment of changing the splitter plate is carried out. Two experiments are carried out by changing the splitter plate, especially changing the material of splitter plate and the number of lower plates of the splitter plate. In the case of changing the material of the splitter plate, the analysis is conducted according to the thermal conductance. In the case of changing the number of lower plates of the splitter plate, the number of plates and their spacing are variables. Analyzing the results of the dielectric recovery voltage experiment, in the initial period, copper plates have the best value that shows 102.1% improvement compared to normal and Al shows 59.8% improvement compared to normal. These increases are related to the thermal conductivity of the three electrode materials. In the case of changing the number of lower plates of the splitter plate, the 8-plates and 9-plates show 84.5% and 36.1% increases compared to normal, respectively, in the initial period. It can be seen that too many plates interfere with heat dissipation. Since this study studies performance improvement during the initial period, there is not much difference in the later period. This is consistent with the experimental results. In this study, an experimental basis is provided for the dielectric recovery strength from a low-voltage circuit breaker. It is expected that this will contribute to the research to improve the dielectric recovery capability of the circuit breaker.

A molded case circuit breaker (MCCB) is one of the most important factors for safety to protect a load from overcurrent in a power distribution system. MCCB, which is mainly installed in switchboards and distribution boxes, may be affected by external temperatures and magnetic fields, but the above factors are still excluded from product standards and performance evaluation. This paper is the result of experimenting and studying the negative effects of these external temperatures and external magnetic fields on MCCB with short-circuit characteristic and dielectric recovery strength. As a result of temperature, it can be found that both short-circuit characteristic and dielectric recovery strength change linearly in accordance with the external temperature. The ratio of the values of 35 °C to 25 °C and 45 °C to 25 °C show the following results. t₁₀, t₂₁, and t₃₂ are 1.58, 1.53, and 1.79, respectively, in short-circuit characteristics and t_i, t_m, and t_l are 1.59, 1.69, and 1.53, respectively, in dielectric recovery strength. Depending on the external magnetic field, the short-circuit characteristics decreased by 8.56% only in the t₂₁ period. The dielectric recovery strength decreases by 4.92% in the initial section (t_i) and 14.45% in the later section (t_l), respectively. It has been confirmed that the external magnetic field interferes with the emission of hot gas.

Recently, as interest in eco-friendly distributed power has increased, studies on the improvement of the performance of breakers such as DC breakers and on the reliability of existing AC breakers have been actively conducted. To improve the performance and reliability of these breakers, this paper conducted the analysis of characteristics of a low voltage circuit breaker using an external magnetic field. In this experiment, before the current-zero point, the cut-off time to improve the breaker performance is shortened and after the current-zero point, re-ignition, which is associated with reliability, is suppressed. According to the experimental results, the short-circuit characteristics before current-zero show a significant difference of 0.13 ms in the t₂₁ section, and the dielectric recovery strength after current-zero shows a 13.3% performance improvement in the latter half of the DRV (dielectric recovery voltage) V-t curve. This result has significant meaning because it can be easily improved under the control of the external magnetic field. Hence, it can be applied to the interruption performance improvement of breakers through detailed research in the future.

Hybrid circuit breakers are the most promising circuit breakers among DC circuit breakers. Conventional hybrid circuit breakers complete fault current isolation by converting current to IGBT when fault current occurs. However, in this case, the fault current continues to increase, so the IGBT must be large enough to withstand this current. In addition, in the case of a method of detecting and operating a fault, a delay time of up to hundreds of microseconds occurs, and in a hybrid circuit breaker, this delay time is a very large value. To solve this problem, this paper proposes a hybrid Z-source circuit breaker that operates without delay for low-impedance faults. The proposed breaker is designed to reduce stress on IGBTs and mechanical switches by generating a current zero crossing, as well as to enable the breaker to trip quickly in high-risk cases such as low-impedance fault circuits. Due to the limited environment of the laboratory, we performed 600 V fault isolation experiments. As a result of the experiment, it was confirmed that the proposed circuit breaker successfully isolated the fault within 1.6 ms. The current limiting feature of the Z-source appears to reduce stress on the IGBTs and MOVs used, and it allows for faster fault isolation.