Quality and consumption requirements of electrical steel for UHV power grid projects

UHV mainly refers to the AC power grid of 1000kV and above or the DC power grid of ±800kV and above, which has the advantages of long transmission distance, large capacity, low loss, less land occupation, and transmission capacity of up to 2.4 times to 5 times that of 500kV UHV power transmission. It is called "power highway" and belongs to the "new infrastructure" smart energy infrastructure.

According to the requirements of Q/GDW11744-2017 National Grid enterprise standard, the construction of UHV power grid project will mainly use high magnetic induction oriented electrical steel (HiB), The grades are 23QG080, 23QG085, 23QG090, 27QG085, 27QG090, 27QG095, 27QG100, 30QG100, or higher.

A ±800kV UHVDC transmission project (including two converter stations or a back-to-back converter station) requires a total of about 56 converter transformers, including 14 converter transformers of ±200kV, ±400kV, ±600kV and ±800kV voltage levels. According to the single calculation, the ±200kV converter transformer needs about 150 tons of electrical steel sheet, the ±400kV converter transformer needs about 200 tons of electrical steel sheet, the ±600kV converter transformer needs about 230 tons of electrical steel sheet, and the ±800kV converter transformer needs about 300 tons of electrical steel sheet. In total, a ±800kV UHVDC transmission project requires the use of high magnetic induction oriented electrical steel about 12,320 tons. A single 1000kV UHV AC project (calculated by two substations) requires 6 1000kV single-phase transformers, several medium and high voltage transformers and reactors (the specific number is related to the capacity, the number of lines, etc.), and requires the use of about 2000 tons of high-magnetic induction oriented electrical steel.
The construction of UHV power grid projects has put forward high requirements for electrical steel products. One is the intrinsic performance of the product. Mainly, higher requirements are put forward for magnetic polarization intensity, specific total loss and harmonic specific total loss. For example, the third harmonic of different brands of products, the magnetic induction content is 10%, and the specific total loss is P1.7T(average), which needs to be ≤0.90W/kg~1.15W/kg. The fifth harmonic, the magnetic induction content is 5%, the specific total loss is P1.7T(average), and it needs to be ≤0.84W/kg~1.08W/kg. In addition, the A-weighted magnetostrictive speed level needs to reach Awv17/50(average), ≤58dB(A), and electrical steel is required to improve the internal performance. The second is the quality of plate shape. In terms of longitudinal thickness deviation and transverse thickness deviation of electrical steel, the allowable deviation of nominal thickness of steel strip should be within the nominal thickness of ±0.020 mm. Third, the surface coating quality. First of all, the insulation coating resistance should meet the average value of single-sided measurement, that is, ≥30Ω·cm2 surface; A single minimum value of 5 measurements on a single side must be ≥15Ω·cm2 surface. Secondly, the lowest level of coating adhesion thickness is grade C, and the proportion of coating adhesion reaching the level of grade B in each batch of steel coil sampling samples should be above 40% and above 60%, respectively, and there is no white edge after shearing. In addition, the electrical steel with extremely low iron loss and higher magnetic orientation is required to meet the higher requirements of transformers while reducing noise.

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