ABSTRACT:The article reported the flame-retardant and the mechanical properties of expandable graphite (EG), an intumescent type, and decabrominated dipheny ethane (DBDPE), a gas-phase type of flame-retardant-containing high-density rigid polyurethane foams (RPUF) with a constant density of 0.5g/cm 3 . The results indicated that both EG and DBDPE could effectively interdict the burning of RPUF, besides, the EG exhibited more effective flame retardancy than the DBDPE. When the flame-retardant loadings were 20 wt %, the LOI value of DBDPE-filled RPUF increased to 33 vol %, while, surprisingly, the EGfilled RPUF reached 41 vol %. Unfortunately, when they were both simultaneously added into RPUF, there was not any flame-retardant synergistic effect. Although EG had outstanding flame retardancy, the compressive strength and modulus of 20 wt % EG-filled RPUF dropped to only 9.1MPa and 229.7MPa respectively, which were lower than those of DBDPE (12.4 MPa and 246.8 MPa). The phenomena were ascribed to the different flame-retardant mechanisms of EG and DBDPE, which were verified by scanning electronic microscope (SEM) observation of the burned surfaces. Besides, the dynamical mechanical analysis (DMA) demonstrated that the additions of EG and DBDPE made the glass transition temperature shift to the high temperatures, and the EG-filled RPUF had the higher storage modulus.
A novel directional relay, which is based on apparent surge impedance acquired from initial travelling waves, is proposed in this paper. The phasor of initial voltage and current travelling waves extracted by the S-transform are employed to calculate the apparent surge impedance. The criteria to determine the fault direction consist of two mho circles. One is the forward mho circle which is set according to the back-side busbar surge impedance. The other one is the reverse mho circle which is set according to the forward line surge impedance. The fault direction is determined as per the relationship between the apparent surge impedance and the mho circles. The proposed algorithm was verified using the PSCAD/EMTEDC software. The simulation results allow us to draw a conclusion that the proposed algorithm has the ability of fast and reliably discriminating between the forward faults and the reverse faults under various conditions. Index Terms--Apparent surge impedance, directional relay, S-transform, transmission line, travelling wave.
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