Operability evaluation of electrical wires and cables subjected to simultaneous fire and current loadings

Introduction. Intumescent coatings are used as a means of protection from heat flows, and their mission is to preserve the operability of wires and cables under fire conditions coupled with simultaneous current loading. However, the effect of insulation destruction on the operability of cables has not been studied for the case of a real fire regime.

Goals and objectives. The purpose of the article is to evaluate the experimental operability of electrical wires and cables subjected to simultaneous effects of fire and current loadings.

To achieve this purpose, an experimental testing unit was applied to conduct the experimental testing of wires and cables manufactured by various producers. At the same time, the temperature effect of the heated environment on electrical parameters of wires and cables, such as resistivity, inductance and capacitance, was evaluated.

Theoretical background. In real fire conditions, dependence of indoor temperature, affecting the heating of cable insulation, differs essentially from the same dependencies in cases of various standard fire conditions. Therefore, the insulation destruction process may occur before the coating intumescence starts.

Results and discussion. An experimental testing unit has been developed. This unit allows for the gradual cable heating with a pre-set temperature measurement interval and cable electrical characteristics. Dependencies of resistivity, inductance and capacitance of standard electrical cables on the temperature of the air surrounding the cable are obtained. It’s been discovered that the gradual heating of an electrical conductor or cable eventually leads to a short circuit between its conductive cores and further electric current transmission in electrical wires and cables. It is shown that phases and amplitudes of an input electrical signal can drastically change before the short circuit.

Сonclusions. The simultaneous effect of fire and current loadings on standard electrical wires and cables causes a short circuit in the temperature range, in which no intumescence of flame retardant coatings is initiated on the insulation surface. Therefore, these coatings can ineffectively maintain the operability of electrical wires and cables.

1. Lebedchenko O.S., Zykov V.I., Puzach S.V. Assessment of operation of safety channel signal cables at nuclear power plants under fire conditions. Pozharovzryvobezopasnost/ Fire and Explosion Safety. 2020; 29(4):51-58. DOI: 10.22227/PVB.2020.29.04.51-58 (rus).

2. Lebedchenko O.S. Assessment of ensuring correct operation of nuclear power plant safety channel cables in fire conditions. Roitman readings : Collection of Materials of the 8th Scientific and Practical Conference. Moscow, March 5, 2020. Moscow, Academy of GPS of EMERCOM of Russia, 2020; 72-75. URL: https://elibrary.ru/item.asp?id=42880351 (rus).

3. Lebedchenko O.S., Puzach S.V., Zykov V.I. The application efficiency of intumescent coatings for po wer cables of safety systems of nuclear power plants under fire conditions. Pozharovzryvobezopasnost/Fire and Explosion Safety. 2021; 30(4):3647. DOI: 10.22227/0869-7493.2021.30.04.36-47 (rus).

4. Puzach S.V., Akperov R.G., Lebedchenko O.S., Boldrushkiev О.B. Evaluation of the toxicity of flame retardant signal cables in case of fire in the industrial premises. Occupational Safety in Industry. 2022; 5: 75-80. DOI: 10.24000/0409-2961-2022-5-75-80 (rus).

5. Zykov V.I., Anisimov Yu.N., Malashenkov G.N. Fire protection of electrical networks from leakage currents. Reducing the Risk of Loss of Life in Fires : materials of the XVIII scientific­practical Conf. Part 1. Moscow, VNIIPO, 2003; 182-185. (rus).

6. Smelkov G.I. Fire safety of electrical installations. Moscow, Cable Publ., 2009; 328. (rus).

7. Meshchanov G.I., Kholodnyy S.D. Analysis of the burning characteristics of polymer insulation of cables during their group laying. Science and Technology. 2010; 5(324):10-14. (rus).

8. International atomic energy agency, benchmark analysis for condition monitoring test techniques of aged low voltage cables in nuclear power plants; final results of a coordinated research project. IAEA-TECDOC1825. Vienna, 2017; 192.

9. NEA/CSNI/R(2018)8. Cable ageing in nuclear pow er plants. Report on the first and second terms (2012–2017) of the NEA Cable Ageing Data and Knowledge (CADAK) project. Nuclear energy agency committee on the safety of nuclear installations. December 6, 2018; 58. URL: https://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=NEA/CSNI/R(2018)8&docLanguage=En

10. Csanyi E. Internal electrical systems within nuclear power plant stations (power sources). EEP — Electrical Engineering Portal. April 29, 2019. URL: https://electrical-engineering-portal.com/electrical-systems-nuclear-power-plant-stations

11. Finger V. Achievements in the field of testing electrical equipment for fire resistance. Journal of Electrical Insulation EEE. 1986; 2(4):128.

12. Cable research in light water reactor related to mechanisms of cable degradation: understanding of role of material type, history, and environment, as well as accelerated testing limitations. US DOE/NRC/EPRI, 2013.

13. Assessing and managing cable ageing in nuclear power plants. NP-T-3.6. Vienna, International Atomic Energy Agency, 2012.

14. SAND 2013-2388. NPP cable materials: review of qualification and currently available ageing data for margin assessments in cable performance. Albuquerque, NM, Sandia National Laboratories, 2013.

15. SAND 2015-1794. Submerged medium voltage cable systems at nuclear power plants: A review of research efforts relevant to ageing mechanisms and condition monitoring. March 2015.

16. CNSC, 13395-REP-00001. Ageing Management of Cable in Nuclear Generating Stations. September 2012.

17. Pekhotikov V.A., Bolodyan I.A., Ryabikov A.I., Gruzinova O.I. Fire on Ostankino TV tower in 2000. Chronicle of events. Pozharnaya Bezopasnost’/Fire Safety. 2017; 4:108-112. URL: https://elibrary.ru/item.asp?id=30775584

18. Xianjia Huang, Yuhong Wang, Wuyong Zeng, Lan Peng, Anthony CH Cheng, WK Chow. Compartment temperature estimation of a multiple-layer cable tray fire with different cable arrangements in a closed compartment. Journal of Fire Sciences. 2019; 37(4-6): 303-319. DOI: 10.1177/0734904119860410

19. Hostikka S., Matala A. Modelling the fire behavior of electrical cables. SMIRT 19th, 10th Post Conference Seminar on “Fire Safety in Nuclear Power Plants and Installations”. Toronto, August 2007.

20. Babrauskas V., Peacock R.D., Braun E., Bukowski R.W., Jones W.C. Fire performance of wire and cable: Reaction to fire tests – a critical review of the existing methods and of new concepts. NIST Technical Note 1291. 1991.