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Dimensioning of Electrical Clearance of OHL Using Correlation between Weather Condition and Lightning Strike Probability

Rusek, B. and Steevens, S. and Kleinekorte, K. and Hannig, M. and Balzer, C. and Hinrichsen, V. and Neumann, C. (2018):
Dimensioning of Electrical Clearance of OHL Using Correlation between Weather Condition and Lightning Strike Probability.
In: Cigré Session 2018, Paris, 26.08.2018 - 31.08.2018, [Conference or Workshop Item]

Abstract

This paper presents a new approach for dimensioning of electrical clearance for 380kV overhead lines. Its principle is based on the circumstance that lightning strikes, i.e. fast front overvoltage surges, only occur at weather conditions, which significantly differ from the standard weather conditions. Ordinary the dimensioning of electrical clearance is performed for standard weather conditions. Detailed analyses allow using electrical clearances resulting from slow front overvoltages only, which are significantly lower comparing to fast front overvoltages. Therefore the electrical clearance is adapted to the present weather conditions in this approach.

Especially for overhead lines, which have been designed for relatively low operating conductor temperatures of, e.g. 60°C, an increase of the line ampacity can be achieved by temporary reduction of electrical clearance, without reducing the operational safety. The analysis shows that the probability of lightning strike to the lowest conductor on the tower, which restricts the ampacity of the line, is very low. Additionally, back flashovers are very rare events, which practically do not occur if the footing resistance of tower is lower than 10 Ω, which is the case for most of the towers of the considered network. Both events only occur during thunderstorms, where heavy loaded conductors are cooled down by bad weather conditions, so that lightning strikes occur at time instants when the conductor has come back to the original sag, i.e. the standard electrical clearance is fulfilled.

The cooling amounts approximately 20°C, which in typical line spans corresponds to a change in sag between 0.46 m and 0.7 m. Due to the cooling effects, the current carrying ampacity of the considered overhead line can be increased by about 30 %.

Item Type: Conference or Workshop Item
Erschienen: 2018
Creators: Rusek, B. and Steevens, S. and Kleinekorte, K. and Hannig, M. and Balzer, C. and Hinrichsen, V. and Neumann, C.
Title: Dimensioning of Electrical Clearance of OHL Using Correlation between Weather Condition and Lightning Strike Probability
Language: English
Abstract:

This paper presents a new approach for dimensioning of electrical clearance for 380kV overhead lines. Its principle is based on the circumstance that lightning strikes, i.e. fast front overvoltage surges, only occur at weather conditions, which significantly differ from the standard weather conditions. Ordinary the dimensioning of electrical clearance is performed for standard weather conditions. Detailed analyses allow using electrical clearances resulting from slow front overvoltages only, which are significantly lower comparing to fast front overvoltages. Therefore the electrical clearance is adapted to the present weather conditions in this approach.

Especially for overhead lines, which have been designed for relatively low operating conductor temperatures of, e.g. 60°C, an increase of the line ampacity can be achieved by temporary reduction of electrical clearance, without reducing the operational safety. The analysis shows that the probability of lightning strike to the lowest conductor on the tower, which restricts the ampacity of the line, is very low. Additionally, back flashovers are very rare events, which practically do not occur if the footing resistance of tower is lower than 10 Ω, which is the case for most of the towers of the considered network. Both events only occur during thunderstorms, where heavy loaded conductors are cooled down by bad weather conditions, so that lightning strikes occur at time instants when the conductor has come back to the original sag, i.e. the standard electrical clearance is fulfilled.

The cooling amounts approximately 20°C, which in typical line spans corresponds to a change in sag between 0.46 m and 0.7 m. Due to the cooling effects, the current carrying ampacity of the considered overhead line can be increased by about 30 %.

Journal or Publication Title: CIGRE SESSION 2018 Papers
Uncontrolled Keywords: Electrical clearance, insulation co-ordination, overhead lines, slow front overvoltage, fast front overvoltage, increase of OHL ampacity
Divisions: 18 Department of Electrical Engineering and Information Technology
18 Department of Electrical Engineering and Information Technology > Institute for Electrical Power Systems > High Voltage Technology
18 Department of Electrical Engineering and Information Technology > Institute for Electrical Power Systems
Event Title: Cigré Session 2018
Event Location: Paris
Event Dates: 26.08.2018 - 31.08.2018
Date Deposited: 19 Sep 2018 09:52
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