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.
Supercapacitor Cycle Life Equalization in a Microgrid Through Flexible Distribution of Energy and Storage Resources
Industrial microgrids functioning under islanded mode of operation are often subjected to large and fluctuating demands from loads such as crushers, excavators, and steel rolling mills. This paper studies the supercapacitor (SC) cycle life when multiple small rated but distantly located distributed energy resources are supplying a cement plant crusher-conveyor load in the islanded operation of the microgrid. Each DER consists of a fuel cell (FC) supplemented with a SC. After having carried out extensive modeling, simulation, and analysis, this paper demonstrates that the SC cycle life can be equalized by employing the cooperative framework of flexible distribution of energy and storage resources.
An empirical method for determining transient temperatures of buried cable systems [includes discussion]
This paper endeavors to describe a method for determining the temperature of a buried cable as the load cycle varies and how it is possible to determine the attainment factor for a variable load. It is not necessary to go through the detailed calculations for each case as was done for the paper in order to show that various types of systems and different load cycles follow a pattern that can be expressed in a single equation. It is recognized that this empirical method for determining the transient temperature of a buried cable is not as exact as the strict mathematical analysis, yet it gives results that can be accepted practically and as accurate as the accuracy of the thermal constants that are used.