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The present work is intended to investigate the influence of polymer material on arc in short circuit fault. Influence of polymer plates, made from Al 2 O 3 , PE (polyethylene), POM (polyoxymethylene), PBS (polybutylenesuccinate), PA66 (polyamide 66) installed in the vicinity of arc column, on arc properties was investigated experimentally. Voltage of arc initiated between the parallel polymer plates were measured in the range of several kA. In addition, composition of gas ablated from the polymer plates during the current interruption was analyzed. Figure 1 shows a schematic diagram of experimental equipment. Electrodes are made of Cu-W alloy and they are connected with a copper wire 0.2 mm in diameter. A short-circuit current with a frequency of 47 Hz is supplied from a 2000 µF condenser-bank through both a 4.26 mH reactor and a step-down transformer. A peak value of the prospective breaking current is 9.7 kArms.The interrupting characteristics in various materials are shown in Fig. 2. In case of POM plates, the peak value of the arc voltage is higher than any other polymer plate. The higher arc voltage leads to the higher current limiting performance, therefore, the peak value of the arc current is the smallest at POM plate. Table 1 presents the composition of the gas ablated from the polymer plates during the current interruption. These experiments were carried out in the sampling bag backfilled with N 2 to distinguish the ablated gas from the gas included in the air. The results indicate that the major composition of ablated gas was H 2 and CO.Based on these results, we consider that the arc voltage depends on the quantities of the H 2 gas. Namely, it is assumed that the electrical conductivity of arc is decreased by the cooling efficiency of H 2 , and then the arc voltage is increasing. To investigate this First, the relationship between the transport properties of ablated gas and temperature of the arc column is examined under the assumption of wall-stabilized arc. It is found that the temperature of arc column depends on the thermal diffusivity of high temperature gases. Arc column consists of H 2 and CO mixture gas, and the thermal diffusivity of H 2 is ten times as large as CO.Second, the temperature distribution of arc column is measured by the two-line method. It is found that the estimated temperature of arc column with POM plates is lower than other plates. Table 1. Analysis of ablated gas composition -1 -

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We have developed a high‐speed fault current limiting equipment for a 6 kV distribution system. The main components of this equipment are a high‐speed vacuum switch (VCB) and gate turn‐off thyristors (GTO) connected in parallel, and a current limiting impedance with low linear resistance in parallel with the switch. The usual load current is carried by the VCB. In case of a power system fault, the fault current is commutated to and interrupted by the GTO on opening the VCB. Tests confirm that the equipment can interrupt an estimated short‐circuit current of 13 kArms by limiting to less than 3.5 kAp. The interrupt time was less than 2 ms. This response is about 100 times faster than that of conventional mechanical circuit breakers. The fast interruption current limiter can protect distribution systems within a few ms of a severe short circuit fault occurrence. The primary operational benefit of this equipment is the reduction of instantaneous voltage drop at the bus or on sound lines and of current stress on power system equipment during a power failure. © 1998 Technica, Electr Eng Jpn, 125(3): 11–21, 1998