Emmanuel I. Koufakis

Calculation of the activation energy of oil-paper insulation in a distribution transformer

This article presents measurements of insulating resistance in distribution transformers, at various temperatures, from which the activation energy of the oil-paper system is calculated.

A Wildfire Model for the Estimation of the Temperature Rise of an Overhead Line Conductor

Fires in open land covered with grass, brush, or timber are often called wildfires. During a wildfire, the overhead conductors of a passing through distribution line suffer a thermal stress that deteriorates their mechanical properties. This paper presents a fire model that allows the estimation of the temperature rise of the conductors if we know some characteristics of the fire. The knowledge of the temperature rise is necessary for the study of the effects on the overhead line conductors.

Magnetic field measurements near a compact kiosk type substation

The last decades the concern of the public, regarding the possible affects from the exposure to magnetic and electric fields, has grown considerably. This is because the generation, transmission and distribution of electric power are accompanied with the presence of the above mentioned fields. This paper attempts to illustrate the values of the resultant magnetic field in the low frequency range, near a compact kiosk type substation 630KVA, 20–0.4 kV. The measurements were performed in a park, in the city center of Chania, Greece, during summer time. All measured magnetic field values were lower in comparison to the value of 100µT introduced by ICNIRP.

Power flow in PME distribution systems during an open neutral condition

The open neutral condition, in distribution networks, can cause significant damage to customer installations. Due to this, the continuity of the neutral conductor is important to the power utilities. In this paper, a power flow algorithm for three-phase four-wire distribution networks with protective multiple earthing (PME), during an open neutral condition, is presented. This algorithm is based on a modified backwards-forwards technique. Additionally, the return current flow is explicitly modeled. Results from three different distribution feeders with different load unbalance and topology are presented and discussed. Furthermore, the effects of the grounding resistances, the load model (constant admittance or constant power), and the neutral breakage point (abruption point) on the voltage levels, are investigated.

High-Voltage Lines in Fire Environment

This letter concerns the change in bending which can manifest in a high-voltage line, when it lies in a fire environment. It is shown that in the case where aluminum conductors steel-reinforced conductors attain a temperature of more than 500°C, a drastic fall of the steel core mechanical strength occurs, resulting in permanent elongation of the line which drastically decreases the clearance from the underlying vegetation.

Magnetic-Field Measurements Near Two-Pole-Type Distribution Substations

This paper presents the mean values of the resulting magnetic field in the low-frequency range, which were recorded during spring and summer near two-pole-type distribution substations in urban areas. The mitigation of the magnetic field that was achieved after covering the low-voltage (LV) fuse boxes with thin aluminum plates is also presented. The mean attenuation achieved is approximately 23% during spring and 18% during the summer at the region of up to 30 cm from the substations and at a height of 1.0 m from the ground, at the measuring points near the LV fuse boxes. All of the measured magnetic-field values that were observed were lower in comparison with those specified as limits and introduced by ICNIRP.

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.