Експериментальні дослідження процесу термічного ураження залізобетонних опор струмами однофазного замикання на землю

Abstract

EXPERIMENTAL STUDY  OF THERMAL SHOCK OF REINFORCED CONCRETE PILLARS BY CURRENTS SINGLE-PHASE GROUND FAULT

1. A.   Kvitsynskyy, O. Shelimanova, V. Santossky

In length, 10 kV air lines (AL) in rural areas on reinforced concrete pillars with ultrasonic currents up to10 Aexceed the length of allALsubstrates with a voltage of more than 1 kV. The neutral grounding of such electrical networks is one of the issues discussed during the last 10 to 15 years. The permissible duration of single-phase earth faults (SEF) in networks with isolated neutral and grounding currents up to10 Ain post-Soviet countries is not established.

The purpose of the research - depending on the ground resistance and current strength of the ultrasound to normalize the permissible duration of the regime of ultrasound, which does not violate the thermal stability of the supports.

The research was carried out by the staff of the UkrSilEnergoProject Institute.

According to our research, the minimum initial power from which the process of thermal damage to the underground part of the reinforced concrete support in the networks of 6 - 20 kV can begin and continue in the future, is:

1,5 - 1,8 kW - in case of support in soils with ρz ≤ 50 Ом ∙ m (chernozems with a humidity of 16%);

4,5 - 5,0 kW - in the case of support in soils with ρz - from 1000 ohm ∙ m to 1500 Ω m (sand with humidity 3 - 4%).

Conclusions

1. The isolated neutral of the 6-20 kV network with the currents of the SEF  to10 Ashould not be grounded through a high-resistance resistor if the network has air lines on reinforced concrete supports with installed pins and supports, whose resistance is not normalized, and provided with natural conductivity underground part of the support.

2. For networks 6 - 20 kV it is necessary to develop guidance documents for the determination of the permissible time of existence of the SEF  to prevent the thermal damage of the underground part of the support.

3.  In networks of 20 kV, capacitive currents compensation should be used starting from 5 amperes and the limitation of the lifetime of the SEF for four hours.

4. Inorder to reduce the number of cases of ultrasound in the intermediate supports of a 20 kV overhead line, rod insulators shall be installed, and anchor-pendant on anchors.