DIAGNOSTICS AND TESTING OF CABLE INSULATION

Kabelski sistemi prinašajo številne prednosti, vendar hkrati tudi težave, ko pride do okvare na kablovodih. Napak na kabelskem omrežju tako ne vidimo, saj je kabel pod zemljo, brez ustreznih merilnih instrumentov pa se lokacije okvare ne more določiti. Zanesljivost omrežja se lahko poveča z izvajanjem različnih diagnostičnih meritev in spremljanje delnih razelektritev (DR) je le ena od možnih poti. DR je lokalen preboj med dvema elektrodama, ki nista v fizičnem stiku, in indikator porajajočih se defektov v izolaciji ter velja za najboljši indikator dotrajanosti izolacije na SN- in VN-kablih. Kljub hitremu napredku in razvoju merilne tehnike še vedno mnogokrat naletimo na ovire in težave, saj ugotovimo, da realne možnosti zaradi najrazličnejših vzrokov niso usklajene z željami uporabnikov. Problematiko DR najpogosteje srečamo na elektroenergetskem področju in želja upravljalcev elektroenergetskih naprav je imeti naprave s čim manjšim deležem DR, če pa so že prisotne, jih želimo nadvse hitro odkriti in odpraviti. Še bolje bi bilo, če bi lahko določili preostalo življenjsko dobo določene naprave. Tu se želje in dejanske možnosti močno razhajajo. V nalogi bom predstavil razloge, zakaj je diagnostika na kabelskih sistemih potrebna in s katerimi merilnimi metodami si lahko pri tem pomagamo ter so v tujini pri rednem vzdrževanju že uveljavljene. Opisal bom prve izkušnje na tem področju v našem podjetju Elektro Gorenjska, saj smo bili prvi izmed elektrodistribucijskih podjetij, ki smo z nakupom večkanalne on-line naprave LPD-monitor pristopili k diagnostiki kabelske izolacije.Cable systems bring many benefits, but there are also some disadvantages, particularly in the case of malfunction of the cable conduits. Such defects cannot be seen as the cable network is below the ground. Without the use of the appropriate measuring instruments, the location of the defect cannot be determined. The reliability of the network may be increased by implementing various diagnostic measures – one possible measure is the monitoring of partial discharges (PD). The PD is a localised electrical discharge which bridges the insulation between two conducting electrodes, which are not in direct contact, and is an indicator of defects in the insulation and thus the primary indicator of a breakdown of the insulation of MV- and HV-cables. Despite the rapid progress and improvement of measuring techniques we continue to encounter obstacles and problems when the reality of the situation does not meet the requirements of the users. The PD problem is most often present in electricity power networks and the network operators prefer to use equipment on which PD occurrences are rare, or can at least be easily discovered and eliminated. Another preference is the possibility of determining the service life of a certain installation. This is an area where the existing measures do not meet the requirements. In my thesis I will attempt to show why diagnostic measures are necessary for cable systems and which measuring methods should be used – many are already in use abroad as a part of ordinary maintenance. I will describe how our company – Elektro Gorenjska – is dealing with these issues, as we were one of the first companies to buy a multi-channel online LPD-monitor to help deal with the diagnostics of cable insulation