Derating of cables at high temperatures

Olavi Keski-Rahkonen, Jouni Björkman, Juho Farin

Research output: Book/ReportReportProfessional

3 Citations (Scopus)

Abstract

A method to characterize behaviour of cables used in nuclear power plants at temperatures exceeding the long-term rating was developed. The problem is to predict how long and at what temperatures cables function in emergency situations. The structure and materials of the relevant cables were reviewed and the properties of these materials at high temperatures were described from literature sources. The physical and chemical processes to be expected were outlined for designing tests. Initially we carried out a real-scale equivalent test with a closed circuit, where the pair cable was connected to a pressure transmitter. The instrument PVC cable under investigation worked normally up to 196 °C, where a short circuit occurred, and leakage current suddenly rose to a high value. However, we could not get any evidence of continuous insulation derating from room temperature to the short circuit temperature. This may be due to the experimental arrangements not being sensitive enough to slight phenomenan or to leakages at connections in the electrical circuit. In order to obtain data about the conductivity of PVC cable insulation at elevated temperatures, a part of the open circuit was heated in a test furnace step by step from room temperature to the short circuit temperature region of 200 °C. We discovered leakage current and insulation conductivity improvement in the PVC cable by using a sensitive electrometer and an insulation resistance meter applied in the open circuit experiment for pure cable. Electrical conductivity of PVC cable insulation materials from the literature and electrical conductivity of the PVC cable insulation layer as a function of inverse absolute temperature match quite well. The first series of tests was carried out for a PVC cable to check the validity of the theory and the test method. The testing programme continued and included seven different types of cables.
Original languageEnglish
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Number of pages61
Edition2nd, rev.
ISBN (Electronic)951-38-5044-7 (1st electronic ed.), 978-951-38-7101-7 (2nd electronic ed.)
ISBN (Print)951-38-5043-9
Publication statusPublished - 1997
MoE publication typeNot Eligible

Publication series

NameVTT Publications
PublisherVTT
No.302
ISSN (Print)1235-0621
ISSN (Electronic)1455-0849

Fingerprint

Cables
Polyvinyl chlorides
Insulation
Temperature
Short circuit currents
Networks (circuits)
Leakage currents
Electrometers
Nuclear power plants
Transmitters
Furnaces
Testing

Keywords

  • power lines
  • cable insulation
  • fire safety
  • nuclear power plants
  • high temperature tests

Cite this

Keski-Rahkonen, O., Björkman, J., & Farin, J. (1997). Derating of cables at high temperatures. (2nd, rev. ed.) Espoo: VTT Technical Research Centre of Finland. VTT Publications, No. 302
Keski-Rahkonen, Olavi ; Björkman, Jouni ; Farin, Juho. / Derating of cables at high temperatures. 2nd, rev. ed. Espoo : VTT Technical Research Centre of Finland, 1997. 61 p. (VTT Publications; No. 302).
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Keski-Rahkonen, O, Björkman, J & Farin, J 1997, Derating of cables at high temperatures. VTT Publications, no. 302, 2nd, rev. edn, VTT Technical Research Centre of Finland, Espoo.

Derating of cables at high temperatures. / Keski-Rahkonen, Olavi; Björkman, Jouni; Farin, Juho.

2nd, rev. ed. Espoo : VTT Technical Research Centre of Finland, 1997. 61 p. (VTT Publications; No. 302).

Research output: Book/ReportReportProfessional

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T1 - Derating of cables at high temperatures

AU - Keski-Rahkonen, Olavi

AU - Björkman, Jouni

AU - Farin, Juho

N1 - Project code: R5SU00480

PY - 1997

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N2 - A method to characterize behaviour of cables used in nuclear power plants at temperatures exceeding the long-term rating was developed. The problem is to predict how long and at what temperatures cables function in emergency situations. The structure and materials of the relevant cables were reviewed and the properties of these materials at high temperatures were described from literature sources. The physical and chemical processes to be expected were outlined for designing tests. Initially we carried out a real-scale equivalent test with a closed circuit, where the pair cable was connected to a pressure transmitter. The instrument PVC cable under investigation worked normally up to 196 °C, where a short circuit occurred, and leakage current suddenly rose to a high value. However, we could not get any evidence of continuous insulation derating from room temperature to the short circuit temperature. This may be due to the experimental arrangements not being sensitive enough to slight phenomenan or to leakages at connections in the electrical circuit. In order to obtain data about the conductivity of PVC cable insulation at elevated temperatures, a part of the open circuit was heated in a test furnace step by step from room temperature to the short circuit temperature region of 200 °C. We discovered leakage current and insulation conductivity improvement in the PVC cable by using a sensitive electrometer and an insulation resistance meter applied in the open circuit experiment for pure cable. Electrical conductivity of PVC cable insulation materials from the literature and electrical conductivity of the PVC cable insulation layer as a function of inverse absolute temperature match quite well. The first series of tests was carried out for a PVC cable to check the validity of the theory and the test method. The testing programme continued and included seven different types of cables.

AB - A method to characterize behaviour of cables used in nuclear power plants at temperatures exceeding the long-term rating was developed. The problem is to predict how long and at what temperatures cables function in emergency situations. The structure and materials of the relevant cables were reviewed and the properties of these materials at high temperatures were described from literature sources. The physical and chemical processes to be expected were outlined for designing tests. Initially we carried out a real-scale equivalent test with a closed circuit, where the pair cable was connected to a pressure transmitter. The instrument PVC cable under investigation worked normally up to 196 °C, where a short circuit occurred, and leakage current suddenly rose to a high value. However, we could not get any evidence of continuous insulation derating from room temperature to the short circuit temperature. This may be due to the experimental arrangements not being sensitive enough to slight phenomenan or to leakages at connections in the electrical circuit. In order to obtain data about the conductivity of PVC cable insulation at elevated temperatures, a part of the open circuit was heated in a test furnace step by step from room temperature to the short circuit temperature region of 200 °C. We discovered leakage current and insulation conductivity improvement in the PVC cable by using a sensitive electrometer and an insulation resistance meter applied in the open circuit experiment for pure cable. Electrical conductivity of PVC cable insulation materials from the literature and electrical conductivity of the PVC cable insulation layer as a function of inverse absolute temperature match quite well. The first series of tests was carried out for a PVC cable to check the validity of the theory and the test method. The testing programme continued and included seven different types of cables.

KW - power lines

KW - cable insulation

KW - fire safety

KW - nuclear power plants

KW - high temperature tests

M3 - Report

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BT - Derating of cables at high temperatures

PB - VTT Technical Research Centre of Finland

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ER -

Keski-Rahkonen O, Björkman J, Farin J. Derating of cables at high temperatures. 2nd, rev. ed. Espoo: VTT Technical Research Centre of Finland, 1997. 61 p. (VTT Publications; No. 302).