Response of power cables to fast transient loads
The most accepted standards for ampacity of power cables consider only steady-state loads. In "Cable Sizing for Fast Transient Loads," R.E. Henry, the transient temperature response of cables is addressed when installed in tray and conduits and undergoing fast transient heating. Herein, the fast transient work is extended by presenting how power cables respond to short heavy loads. Fast heating is usually found with variable frequency drives that deliver varying amounts of occasional non-periodic high torque, or with rectifiers that deliver occasional heavy currents to equipment, like melting of scrap in an arc furnace. Transient temperature rises are calculated for four sizes of cables subjected to spikes of kiloampere currents of short durations. These peak temperature rises are tabulated in a summary. With the rms value of a transient current profile and the NEC ampacity tables, this tabulation provides the means for a rapid cable size comparison, and cable size selection. The linearity and proportional responses of these peaks rises show that they are independent of how the cables are installed. Hence, this method of sizing feeders for fast transient loads applies to all installations of cables covered in the NEC ampacity tables.
Transient nonlinear thermal stability analysis of metro cable under pulse power
The load of metro cable system varies a lot from morning rush hours to the evening closure time. With many trains hopping in the rush hours, the long term and economical short term thermal stability become a big issue as a result of the large difference between thermal time constant and the electrical time constant of cable. Based on a 10kV three-core XLPE metro power cable model, the theoretical thermal capacity was calculated according IEC standard. Then, a Finite Element Method (FEM) was employed to analyze the transient electro-thermal phenomena, taking into account various types of power loss in cable system and the non-linear electrical conductivity of the conductor. Finally, the thermal distribution inside the cable was presented as a function of time, and the maximum thermal capacity was predicted in metro cable.
The relation of food quantity to rumination behavior.
Preliminary work suggested that the quantity of food ingested by retarded individuals who usually ruminated following meals was related to the frequency and duration of ruminating responses. This possible relation was experimentally examined by systematically varying food quantity from regular portions to satiation levels for three retarded individuals who exhibited high levels of ruminating. A clear functional relation of food quantity to ruminating emerged, with satiation procedures producing rapid and large decreases in the relatively high frequencies and durations of ruminating characteristic of baseline food quantity conditions.