Corona performance of 400 kV bundle conductors and insulator strings

摘要

Since completing the erection of 2 × 400 kV double-circuit overhead transmission line (OTL)interconnecting substations Kainachtal (Austria) and Maribor (Slovenia) in November 1992, there wasa standstill in 400 kV OTL development, design and construction in Slovenia. At the end of 2013,construction of a new 80 km long 400 kV double-circuit OTL Bericevo - Krsko was accomplished.Due to increasing environmental constraints introduced in regulatory requirements, which generallyproduced difficulties in obtaining right of way for new lines, the preparatory R&D activity aiming tofulfill these requirements has initiated.The paper reports the outcome of a comprehensive research activity which involved testing andmeasuring of corona phenomena producing different types and intensity of environmental impacts.Several bundle configurations, including already in use the horizontal twin-bundle conductor(490-AL1/64-A20SA) with spacing 400 mm, were tested in high voltage laboratory (HVL). Anextensive amount of testing data was obtained and evaluated in detail searching for next generation ofthe Slovenian OTL most important component. Testing included different conductor bundle layoutswith standardized conductors, special surface treated (hydrophilic or “silent”) conductors, trapezoidalwire conductors and others. Partial discharges (PD), radio-interference voltage (RIV) and coronaextinction voltage measurements were made in dry and wet conditions. Visual observing, recordingand examination were performed using a special camera. Comparison of the results obtained andresults of the electric field calculations of chosen conductor bundle arrangements was performed.Acoustic noise measurements in different weather conditions near operating OTL fitted with twinbundle conductors (490-AL1/64-ST1A) and triple bundle conductors (475-AL1/25-A20SA) were alsoperformed.A triple conductor bundle (490-AL1/64-A20SA) with spacing 400 mm was chosen and put aspreferred design basis for the future 400 kV OTL in Slovenia taking into account also economicimpact, mechanical aspects, typifying of elements etc. [1].Additionally, the introduction of composite insulators replacing the formerly used cap and pin glassinsulators was made with the same purpose. Low corona insulators strings were selected in order toreduce RIV and to obtain maximum reliability taking into account concepts previously implementedon 400 kV lines in Slovenia. Several different design proposals were evaluated and tested. Coronaperformance of chosen composite insulator set was highly improved [2]. Corona extinction voltagevalue of the existing twin-bundle conductor (490-AL1/64-A20SA) is now significantly lower [2].Some of this way found solutions were immediately implemented in the 400 kV double-circuit OTLBericevo - Krsko project, such as “silent” (hydrophilic) conductors, colored conductors and selectedcomposite insulator strings. For the type tests and factory acceptance tests (FAT) of the hydrophilicconductors a sampling and testing procedure was selected and proposed. These hydrophilic conductorswere installed in two sections of the 400 kV double-circuit OTL Bericevo - Krsko, that will serve as atest site for future OTL audible noise investigations and measurements.During the preparation of samples and follow-on testing that was performed in HVL several findingsand improvements concerning the testing procedure and equipment were also obtained. The compositeinsulators were tested according to IEC 61284 standard, whereas the testing procedure for corona onconductor bundles isn’t standardized. Neither the procedures for measuring of PD, RIV and coronaextinction voltage in wet conditions are standardized. The test object can be exposed to artificial rainduring measurement or just pre-wetted. It was found that booth procedures have some advantages anddisadvantages.Also the method for obtaining of the corona extinction voltage is very nearly defined and described inrelevant standards. It suggests observing and listening to the perceived phenomena. This approachmight be disputable and for this reason the extinction occurrence was verified by measuring electricalmagnitudes of RIV and PD.