Electrical component ignition in a closed enclosure adjacent to a controlled fire

Abstract

Summary Electrical cabinet fires are one of the main fire hazards in nuclear power plants (NPPs). The electrical cabinets are often arranged in rows of adjacent cabinets (ACs) in NPPs. So the ability of a cabinet fire to spread to ACs is a major concern for fire safety. This work aims to investigate the impact on the fire spread of the air gap between two electrical cabinets, the electrical component type contained in the AC, and its ventilation mode. For that purpose, a test device composed of two adjacent steel enclosures was designed in order to reproduce at reduced‐scale adjacent electrical cabinets. This study first reveals that the studied electrical component types spontaneously ignited when their temperature and the incident heat flux reach critical ignition values. These ignition criteria are assessed for each component type. The tests also show that the air gap increase slows down the rise of the side wall temperature of the two enclosures, which delays the ignition time of the electrical components. This work finally highlights that the mechanical ventilation of the adjacent enclosure (AE) has an impact on the ignition conditions. In contrast, the natural ventilation as implemented in the AE has a small effect on these conditions.

Experimental study at reduced-scale of fire spread between electrical cabinets located opposite each other

“…The expanded relative uncertainty for the two HFS was estimated in this study to be ± 15 %. This is consistent with the evaluations given in other fire test conditions [9] and [12] for the same type of sensor. Three cameras were used for these tests.…”

“…The back wall contribution is indeed negligible. Previous research [9] showed that maximum wall temperatures of the BE, for the same fire power of 300 kW, did not exceed 850 K at 300 s. Thus, considering this temperature in Eq. ( 1), as well as a maximum view factor of 0.145 (SD of 0.4 m) for dA to the back wall FdA-BW (see appendix A) and a steel wall emissivity of 0.8, this gives a maximum contribution of 3 kW/m2 to q0, before taking into account the flame absorption.…”

“…The absence of target ignition for T4 was unexpected since the maximum heat flux measured closest to the target, qbil (36 kW/m2, see Fig. 10A) was higher than the critical heat flux, qc,ig (31 ± 3 kW/m2) assessed for the spontaneous ignition of this target type [9]. The video analysis for this test indeed revealed that the sets of TB partially melted and then fell to the bottom of the raised floor before qi),l reached previous qc,ig.…”

“…This allowed to obtain the same maximum fire power per unit volume for the reduced and real-scales. Details of the design study of the BE are given in [9], which used this enclosure for a previous work on fire spread between two adjacent enclosures. In addition, as with the open-door cabinet [8], one panel of the BE, located opposite the right-hand enclosure, was removed (Fig.…”

“…The electrical cabinets in NPPs can commonly be laid out in multiple parallel rows, as found for example in control or switchgear rooms [3]. Several studies [4]- [9] investigated the fire spread between adjacent electrical cabinets. In contrast, little research has addressed a scenario in which electrical cabinets are located opposite each other.…”