• Fire Science and Engineering
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• v.27 no.2
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• pp.1-5
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• 2013

This paper studies on an arc fault interruption control circuit (AFICC) of fault voltage sensing type. The proposed voltage sensing type AFICC (VST_AFICC) is an electrical fire prevention apparatus that operates the existing circuit breaker with sensing the instantaneous voltage drop of line voltage when occurs electrical faults. The existing Earth Leakage Circuit Breaker (ELB), Molded_case Circuit Breaker (MCCB), and Residual Current Protective Devices (RCDs) used in low voltage distributing system don't have protective capability from electric arc faults to be a major factor of electrical fire. In this paper to improve such problems, a new VST_AFICC using the distortion of voltage waveform when occurs electrical faults is proposed to prevent electrical fire. There is characteristic that the control method of proposed apparatus is different from previous current sensing type. The proposed AFICC has merit that is manufactured by small size and light weight. The practicality of a new VST_AFICC is also verified through various operation analysis.

• Fire Science and Engineering
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• v.28 no.5
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• pp.8-13
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• 2014

The purpose of this study is to analyze the damage pattern when overcurrent is applied to a thermal magnetic type molded case circuit breaker (MCCB) using a Primary Current Injection Test System (PCITS). When an overcurrent of 150 A was applied to the PCITS for 5 seconds with the trip bar of an MCCB being damaged, it was found that the surface of the temperature control device (bimetallic strip) positioned at the right was significantly carbonized. When an overcurrent of 300 A was applied to the PCITS for 5 s under the same conditions, the entire temperature control device was deteriorated, becoming flattened and in close contact with the MCCB. When an overcurrent of 450 A was applied to the PCITS for 5 s, the coil of the temperature control device was melted and disconnected. In addition, it was observed that the contacts, the enclosure and upper cover were deformed and there was a trace of carbonization on them. When approximately 3 s had elapsed after an overcurrent of 600 A was applied, white smoke occurred inside the MCCB and a flame was radiated out, after which the overcurrent supply stopped with "phutt" (whomp) sound. It was observed that when the same type of MCCB is damaged by a general flame, the surfaces of its handle, terminal, arc divider (extinguisher) and temperature control device were carbonized uniformly. In addition, it was found that the trip bar of the operating mechanism was melted down and the metal operation pin was moved while being tripped.