Study On Insulation Structure Of Outlet Devices Of HVDC Converter Transformer

By the year2014, a number of±800kV UHVDC transmission projects have put into operation in China. The development of converter transformer valve-side outlet device has been a technical bottleneck for nationalization of converter transformer designing. For converter transformers over±660kV, devices are all imported from foreign countries. Compared with foreign countries, the relevant basic research of converter transformer insulation structure started late in China manufacture, and there are not yet mature research results. Different from the conventional power transformers, valve-side insulation of converter transformers is bearing AC voltage, DC voltage, harmonic voltage and also dynamic DC voltage when started, stopped and polarity reversed. As the critical component, connecting the body and the valve-side DC bushing in converter transformer, stable insulation performance is the crucial factor to guarantee the operation reliability of converter transformer. The main content of this paper is aimed at insulating properties researching of outlet device of converter transformer.The outlet devices of converter transformer over±660kV have not yet achieved domestic designing. Current production are designed by two technical route from foreign manufactures, which is called "open-side" and "close-side" outlet devices. In this paper, these two types of outlet devices are compared and analyzed. Based on±400kV DC engineering practice, with the "close-side" route, a1:1±400kV converter transformer outlet devices has been designed and produced. Through simulation calculation, the insulation margin in the oil gap and along the surface creepage path of the outlet device under AC, DC, and polarity reversal voltage. Three experiment schemes have been put forward. Whit comparison, the "inverse boosting method" combined with AC/DC reexamination was taken to measure the insulation margin of the1:1+400kV converter transformer outlet device for the first time. The inverse withstand voltage is considered-780kV, with the margin value is1.2times the Determination for Taiwan±400kV outlet device model inversion withstand voltage-780kV, margin value is1.2times as the DC testing voltage.After the margin testing, there was a strip inspection of this outlet device. Two surface creepage path led by DC voltage were found on the cardboard screen. Aimed at the weak point reflected by the creepage path, some improving schemes of the local insulation structure of outlet device have been proposed, which has current significance for design of valve-side outlet devices of converter transformers.