Development of the HVDC ±80kV XLPE Cable System and Construction of Test-bed in KOREA

摘要

This paper describes the development of the HVDC ±80kV XLPE cable system capable of 60MW allowable for polarity reversal operation, and construction of test-bed for DC XLPEcable system in Jeju Island in Korea, together with the results of type test.Polyethylene (PE) has excellent dielectric properties, thus cables insulated with cross-linkedpolyethylene (XLPE) have been applied to AC cables. However DC power cables withextruded insulation have not been adopted yet. The insulating performance of extrudedinsulating material used for AC power cable is not suitable for DC operation due to thephenomena of space charge accumulation in the material. Thus many researches have beenconducted to find an effective solution, which decrease a space charge accumulation in thematerials, such as adding a type of conductive inorganic filler or polarized inorganic filler tocross-linked polyethylene (XLPE). We developed nano-composited compound for DC XLPEcable insulation by adding nano sized inorganic filler. The developed insulation materialsshow that a space charge accumulation is decreased dramatically. In order to evaluate anelectrical performance at cable state, we manufactured a mini-model cable which is 4mminsulation thickness and 400 ㎟ conductor, and we found DC and impulse breakdowncharacteristics through statistical data processing.KEPCO, LS Cable & System, LS Industrial Systems and some companies have beendeveloping HVDC technology which is system design technology, operation technology andproducts such as converter system, overhead line, underground cable system, and so on. Toverify long term reliability and stability of those system, test-bed will be constructed in JejuIsland until the end of March 2012, and it will be started field test. DC ±80kV XLPE cableshall be applied for this project. The application of XLPE cable for DC transmission is thefirst project in Korea.We determined the nominal insulation thickness of cable as 12 mm to endure BIL (BasicInsulation Level) which is determined 325kV. Jeju test-bed transmission line is complexhybrid lines which are consisted of about 4.8km long overhead line and 500m longunderground cable. DC overhead line will be installed in one pylons carrying AC 154kVcircuit. To determine BIL, transmission lines including overhead line and underground cable are simulated by EMTP (Electro Magnetic Transient Program), and BIL is determined bysimulation result added margins.In order to verify the mechanical and electrical performances of DC XLPE cable system, wecarried out the type test according to CIGRE recommendations (Electra TB No. 219 :Recommendations for testing DC extruded cable systems for power transmission at a ratedvoltage up to 250 kV[1]). The specimen for electrical tests was consisted of 50m long DCXLPE cable and terminations. This specimen was subject to mechanical preconditioningbending test according to IEC 60840 before starting the electrical test. The electrical testsconsist of load cycle test, polarity reversal test, superimposed switching impulse test,superimposed lightning impulse test and DC voltage test. These test items were executedsequentially on the same specimen. By the result of type test, it was confirmed that thedeveloped cable system has superior mechanical and electrical performances for HVDCtransmission lines. Moreover, to evaluate long term reliability and stability, the cable systemswill be subjected to the field test.