Permanent Design of Power Systems. The Current Impulse: A Characteristic Parameter

The design of an electrical system is permanent and a complex process that must follow the system throughout its complete life. All system components, from the installation and commissioning, are subject to a natural degradation which will lead to deterioration of the electrical and mechanical properties, leading to the end of its life. Therefore, the electrical system, to guarantee a "nominal" performance within an assigned period of time, must be monitored and managed in actual operation. The operation of each component in anomalous conditions occurs if it is affected by an overcurrent. Consequently, overcurrents must be taken into consideration and counted as increases in the natural "loss" of life. In correlation with each overcurrent event, the increase in natural aging can be evaluated. A procedure based on the Arrhenius model of the thermal aging of insulating materials allows to introduce the relative time coefficient (RTC) which evaluates the aging rate variation and to promote a simplified method for an estimate of the loss of life and the residual useful life of insulated electrical cables. As well known, in the case of transient - adiabatic events such as short circuits, the circuit conductors must be affected by a let-through energy not exceeding a specific energy tolerable value. This paper highlights how the conductor’s behavior can also be characterized analyzing the parameter impulse of current tolerable for the conductors.