1. The internal insulation of the valve-side windings, outlet structure,s and bushings of converter transformers will be one of the main challenges to be solved due to the increased voltage level. The valve-side windings are subjected to high mixed AC and DC field strengths, requiring the use of large quantities of insulation materials such as insulationmoldingss. The development and testing of insulationmoldingss for the valve side leads of the ±800 kV converter transformer, the design,n and testing of the main insulation,n andthe turn insulation of the valve windings are the key challenges to be solved in the development of the equipment.
2. DC field equipment insulation problems caused by the high fouling level of the converter station. The fouling of DC equipment accounts for a large proportion of DC field accidents and is a key problem to be solved. According to previous engineering experience and experimental research, due to the fouling characteristics of the DC field, the creepage distance of DC equipment is about two times the creepage distance of AC equipment under the same fouling conditions. With the development ofurbanizationn andindustrializationn, the problem of atmospheric pollution is becoming increasingly serious and the fouling of UHV DC converter stations has reached Class II or even Class III levels, which requires a creepage distance of 70 mm/kV or higher. Under the EHV voltage, the creepage distance required by the standard design exceeds the height that existing manufacturing or operation can withstand. In heavily fouled areas, indoor fields or equipment synthesis are two possible ways to solve the fouling resistance problem. State Grid has made this issue a key research project, conducting actual measurements of fouling under DC field strength at converter sites, determining reasonable and objective DC fouling levels, and conducting in-depth research through practical size tests and other tests to ensure that equipment has a safe and reasonable level of external insulation to ensure safe and stable operation of UHV DC.
For the first time, the State Grid Corporation has proposed a ±800 kV, 4,000amperese, 6.4 million kilowatt series of UHV DC project schemes. Xiluodu, Xiangjiaba, and Jinping use a total of four rounds of ±800 kV UHV DC transmission projects to send out, each with a transmission capacity of 6.4 million kilowatts, which is the highest voltage level and largest capacity DC transmission project in the plan.
Due to the large transmission capacity and high voltage resulting in a large volume of high-end converter transformers and increased transport weight, according to the manufacturer’s conceptual design estimates, the maximum weight of high-end converter transformers at the sending end can reach 360 tons per unit. Due to the transport conditions at the sending end, after technical and economic analysis, the State Grid Corporation has concentrated all three converter stations at the sending end in Yibin City, Sichuan Province, in the site planning of the Jinsha River Outgoing UHV DC Transmission Project, which not only solves the transportation problem of large equipment but also saves the project cost and is conducive to the operation and maintenance of the EHV converter stations.