P.D. Bourkas

Electrical contact overheating under short-circuit currents

Abstract In this paper, a method is proposed, concerning the temperature rise estimation at stationary electrical contacts, operating in the power supply network, during short-circuit. The method consists in the formation of a mathematical model, which simulates the operation of the contact/conductors system under heavy fault currents. The model comprises analytical mathematical expressions that enable temperature estimations lengthwise the aforementioned system. From the analysis results, it can be concluded that the conductor (bar) cross-section is of primary importance as far as overheating is concerned. It is convincingly shown that the equipment deterioration can be delayed by lowering the maximum contact temperature during short-circuit transient phenomena. An approximate equation is also proposed as an extra calculating test for the contact and bar overheating under short-circuit conditions. The proposed model could be a criterion for the selection of conductors and switchgear components.

A model for calculating the temperature of aluminium particles ejected from overhead low-voltage lines owing to a short-circuit

Wildfires, which are uncontrolled fires spreading readily over vast areas, are usually the result of human negligence, arson or lightning. There are cases of fires close to electrical distribution lines for which the network has been blamed. In the present paper, the risk of a wildfire breaking out owing to the temperature of molten metal particles that are possibly created on bare conductors of low-voltage networks in short-circuit faults (unless they are interrupted by the protection systems) is examined. Thus, a mathematical model is proposed for the estimated temperature rise of those molten metal particles ejected from bare conductors of low-voltage overhead lines. Moreover, this model can be applied to medium- or high-voltage networks. The model takes into account the weather conditions and particles’ height above the ground. Further, an arithmetic example for an incandescent particle ejected from aluminium conductors of a low-voltage network is given. According to this example, there is no risk of dead leaves or wood catching fire owing to this particle.

Abruption Cross-Section and Bending Change of ACSR Energy Lines in Fire Environment

An ACSR (Aluminum Conductors Steel Reinforced) power line, when it lies in a fire environment, can manifest a permanent elongation and change in bending, as when the conductors attain a temperature of over 500°C, a drastic fall of the mechanical strength of the steel core is caused. This work is a study about the conductor cross-section at the position of the abruption, in case it occurs. This cross section appears to be approximately 62.5% of the original value. Subsequently, two approximative methods of calculating the bending change of overhead lines are shown.