The Method of Unambiguous Determination of the Design Electrical Load According to the Heating Condition

Abstract

A problem of checking conductors for heating condition in power supply systems in case of random electrical load is considered. A probabilistic model of current is used. The current is considered as a random process with a normal distribution law. It is shown that the existing practice of determining the design load from a ten-minute heating time constant does not provide a reliable solution. It is proposed to use the curve of the effective inertial current versus the heating time constant. Methods to obtain this dependence with a random electrical load are identified. The exact solution is found at the intersection of this curve with the curve of the long-term permissible conductor load versus the heating time constant. The calculations took into account that the scale of standard cross-sections of conductors is discrete. Errors of existing method are evaluated with example of random electrical load with exponential correlation function. It is shown that the error in determining the design electric load and the error in selecting the cross-section of the conductors are different.