Associated with Laxiwa hydropower station

the 800 kV step-up transformer

which directly connects with generator

shall be adopted first in northwest.Some technical considerations are given to solve the problems appeared in design.Besides

according to technical design and preliminary research results

the three single-phase transformers

with a three-column core and a voltage-regulation scope of 800/-3×2.5% kV

are chosen.As the pre-inserting resistance is used in CB and DS

the very fast transient overvoltage produced in GIS will make little influence to the transformer insulation.With the overvoltage level of 800 kV rated voltages in China

preferred rated insulation levels are given.