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Transactions on Electrical and Electronic Materials https://doi.org/10.1007/s42341-020-00201-3

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Condition Assessment of Low Voltage Photovoltaic DC Cables under Thermal Stress Using Non‑Destructive Electrical Techniques Ehtasham Mustafa1   · Ramy S. A. Afia1,2 · Zoltán Ádám Tamus1 Received: 17 November 2019 / Revised: 6 April 2020 / Accepted: 30 April 2020 © The Author(s) 2020

Abstract The output power of the photovoltaic system is heavily dependent on the low voltage (LV) DC cables which are exposed to multiple stresses such as climatic, mechanical, electrical, and thermal stress, hence makes them more exposed to aging as compared to other components in the system. Accordingly, it is essential to monitor the state and know the real cause of the insulation degradation of the cable. The physio-chemical changes inside the insulation during service is attributed to the thermal stress, which the cable has to endure constantly. Traditionally, destructive test techniques have been adopted to study the aging phenomenon in the cable insulation, making them unsuitable for on-line condition monitoring. This research work has been aimed to study the degradation in LV photovoltaic DC cables under thermal stress by measuring the dielectric properties; complex permittivity, tanδ with the change in frequency and decay and return voltage slopes using extended voltage response method. The non-destructive diagnostic methods used are based on the phenomenon of polarization and conduction in the insulation material. The noteworthy change in the values of the imaginary part of permittivity, tanδ at low frequencies, and the overall decrease in the values of return voltage slope showed the change in the structure of the polymer matrix under the stress which was related to the cross-linking based chemical reactions. The results show that the techniques can be adopted for the on-line condition monitoring of the cable for the PV system and the dielectric parameters can be used to study the chemical and physical changes happening inside the material effectively. Keywords  Photovoltaic power system · Low voltage DC cables · Thermal stress · Complex permittivity · Extended voltage response

1 Introduction The share of renewable energy in the over-all world electricity consumption is rapidly growing due to its clean, green and reusable characteristics [1]. The photovoltaic (PV) system is one such renewable energy source out of other available sources which has been recognized as a cost-competitive, safe, environment-friendly, and reliable source of energy. It has been predicted that PV will surpass its competitor wind in new installed capacity in the coming years as a result * Ehtasham Mustafa [email protected] 1



Department of Electric Power Engineering, Budapest University of Technology & Economics, 18 Egry Joszef Street, 1111 Budapest, Hungary



Department of Electrical Power and Machines Engineering, Helwan University, 1 Sherif Street, Helwan, Cairo 11792, Egypt

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of huge price declines in recent times [2–4]