21, rue d’Artois, F-75008 PARIS B1-210 CIGRE 2006 http : //www.cigre.org THERMAL MONITORING OF HIGH VOLTAGE CABLES A.POPOVAC-DAMLJANOVIC, M.Sc EE 1 M.SREDOJEVIC, B.Sc EE Prof. S.NIKOLAJEVIC, PhD EE Z.JANDA, PhD EE Electrical Utility Company, Belgrade E.E. Institute ''Nikola Tesla'', Belgrade Serbia and Montenegro SUMMARY Source substation 220kV/110kV supplies downtown Belgrade via 110 kV cable feeders forming the ring of five substations 110/10 kV. The results of several years of researches on 110 kV cable feeders on Belgrade territory [4,6] have shown that appearance of local thin area of dry soil surrounding 110 kV underground power cables in exploitation must be taken into consideration [2]. These places are marked as critical hot spots. Subsequently, at those spots cable bedding improvement made of special mixture with 2% of cement was done and thermal probes were installed. In this way the measurement of temperature changes in the vicinity of 110 kV cable feeders was enabled at hot spots locally. This was the first stage of research. During the exploitation of 110 kV cables it was shown that, due to faults and increased loads, there is a need for short time overload. This is possible by having favourable conditions in the vicinity of 110 kV cable feeders. Therefore it is necessary to have real thermography pictures of cable in the real time. With that aim, in the second stage of researching, monitoring system was mastered and applied at 110 kV cable feeders for substation 110kV/10 kV ″Belgrade 36″. Monitoring system includes a set of elements, which are installed at hot spots of the power cable route (measuring spots), and an arrangement of elements installed in the substation. The communication between the measurement spot and substation was carried out using optical cables. In this way, users have the possibility for remote observing and analysing of real thermography pictures of the high voltage cable in real time by personal computer located in the substation or/and dispatchers centre and to predetermine maximum permitted overloads using standard IEC 60287. This is important, because in this way the dispatcher has the possibility to allow a short time overload of power cables without endangering the reliability of supply, if the ambient conditions surrounding the cable are favourable. Also, the thermal monitoring system makes it possible to discover new hot spots along the cable route as a consequence of the worse conditions in the vicinity of the cable that aggravated during exploitation. The thermal monitoring system described in this paper is based on the experience and experiments conducted in the Belgrade area by the authors during past several years. KEYWORDS High-voltage cables - Cable route - Temperature - Hot spots - Monitoring system - Thermoelement - Optical cable - Split-core current transformer - Real thermography pictures - Predetermine overload. 1 Aleksandra Popovac-Damljanovic, M.Sc. EE-Gospodar Jevremova 28, 11000 Beograd, apd@edb.eps.co.yu