Veskimetsa-Kopli 110 kV kaabelliini ekraanide maandamise lahenduste võrdlus

Lõputöö mahus on uuritud Veskimetsa-Kopli 110 kV kaabelliini kaabli ekraanide maandamise variante ning võrreldud neid omavahel nii elektrilise kui ka paigalduse ja hooldamise seisukohast. Elektrilisest seisukohast oleks olnud parem ehitada „cross bonding-uga“ kaabelliin, kuna selle tõttu oleksid liinil väiksemad kaabli koormuskaod. Samuti väheneks raha hulk, mis kuluks ainult kaabelliini koormuskadude maksumuse peale. Paigalduse ja hoolduse poole pealt tulevad kahe käsitletud lahenduse vahele suured erinevused ja tulevad välja kindlad plussid ja miinused, mis määravad ka kaabelliini ekraanide kõige efektiivsema maandamise meetodi. Nimelt on „cross bonding“ lahendus Veskimetsa-Kopli kaabelliini asukoha tõttu mitte sobilik. Probleemid tekivad seoses sellega, et kaabelliin paikneb väga lähedal merele ning „cross bondingu“ kaevud oleksid vee all. Kaevude vee all olemine tõstab riski, et niiskus võib sattuda kaabli isolatsiooni vahele ning tekitada kaabli isolatsiooni rikke, mille kõrvaldamine nõuaks spetsialistide sekkumist, keda Eestis lõputöö kirjutamise ajal ei ole saadaval ega ka nende vähese nõudluse tõttu olemas. Töö tulemusena võib öelda, et Veskimetsa-Kopli 110 kV kaabelliini ehitus „both ends bonded“ meetodiga on igati mõistlik, kuna kõrgepinge kaabelliini hooldustööd on väga keeruka iseloomuga ning võtavad kaua aega. Kuna Veskimetsa-Kopli liin asub linnas ning sellel on vajalik kõrge töökindlus, siis saavutatakse see kõige paremini just „both ends bonded“ kaabli ekraanide maandamise meetodiga. Autori seisukoht töö tulemusena on see, et Veskimetsa-Kopli 110 kV kaabelliini ehitamine „both ends bonded“ kaabli ekraanide maandamise meetodiga on väga hästi põhjendatud. Kuid autori soovitus tehtud tööl põhinedes on see, et kuivemates ning mere pinnast kõrgemates kohtades ehitatavad lühemad kõrgepinge kaabelliinidel kasutada „cross bonding“ ekraanide maandamise lahendust, kuna nende kahe erineva meetodiga lahendatud kaabelliinide koormuskadude erinevus on ~17% „cross bonding“ lahenduse kasuks. Samas tuleb silmas pidada seda, et „cross bonding“ lahenduse paigaldus ja hoolduse hind on kallim ning paigaldus on keerukama iseloomuga. Samuti pakub autor kaaluda lahendust, et paigaldada kaabelliinidele vettpidavad, püsivad kaabli muhvi kaevud, et ära hoida niiskuse sattumist muhvidesse ja kaabli kaevus olevatesse seadmetesse.

Thesis gives an overwiev of 110 kV cable screen grounding with cross bonging and both ends bonding screen grounding methods. Calculatios and estimations are made acoording to electrical, mechanical and geological parameters of Veskimetsa-Kopli 110 kV cable line. Thesis looks at negative effects of cross bonding and both ends bonded methods from the point of view of installation and maintenance as well as load losses. From the point of view of load losses cross bonding wold have been a better variant to buildt, as load losses in a cross bonded cable line are lesser than in a both ends bonded system. Cross bonded system would also be more cost efficient from the load loss point of view. However installation and maintenance of Veskimetsa-Kopli cross bonded cable line would be very expensive. Complications come from the fact that the cabe line is near the sea coast which means the cross bonding cabinets would be mostly below water level which is a considerable factor for choosing the method of shield bonding of cables. The reason for the problem is the increased risk of moisture entering the insulating material of cables which causes insulation faults. To remove insulation faults special knowledge and skills are required. At the time when the thesis was written Estonia did not have specialists who have the required knowledge to work with 110 kV cable joints. It is a problem since it makes removing cable insulation faults a long process because the specialists have to come from abroad. As a result of this study it can be said that the choice of both ends bonded cable screen grounding for Veskimetsa-Kopli 110 kV cable line is very reasonable, because of the complications that arise with the complexity of maintenance and construction of a cross bonded system. Veskimetsa-Kopli cabel line is situated in the city of Tallinn and requires high reliability. Higher reliability is best achieved with the both ends bonded cable shield grounding method The author’s opinion as a result of the study conducted in this thesis is that the construction of the Veskimetsa-Kopli 110 kV cable line with the both ends bonding screen grounding method is justified. However author recommends that shorter high-voltage cable lines in drier areas the cross bonded system should be considered as the load losses are ~17% smaller with the cross bonded system. At the same time cable line designer should keep in mind that the installation and maintenance cost of the cross bonding solution is more expensive and installation is more complex in nature. Also installation of water proof and permanent cable wells for joints and transpositions of cables and cable screens on high voltage cable lines should be considered.