Insulation Design of High Voltage and Large Capacity Power Supply Transformer

Abstract At present, the highest voltage level of DC circuit breakers in the world is 535kV. With the construction of 800kV multi-terminal flexible DC project, the demand for DC circuit breaker with higher voltage level is put forward. The voltage level of valve base power supply transformer as the power supply component of the DC circuit breaker is increased to 800kV. Single-section pendulum structure, single-section 100kV and 50kV schemes used at 535kV cannot meet the demand. An 800kV valve base power supply transformer scheme of four 200kV gas-insulated transformers in series is proposed. Its insulation design is also carried out. Firstly, the topology of hybrid DC circuit breaker power supply system and the structure of power supply transformer were described. Secondly, the design of power supply transformer insulation was carried out. Finally, the power supply transformer insulation was tested and verified. The results show that: SF6 power supply transformer internal insulation withstand voltage needs to be multiplied by the multiplication factor. The electric field strength limit of SF6 obtained by experiments is more than 1.5 times of the empirical design value. The internal field strength design of the 200kV power supply transformer takes into account the operating and seismic conditions, and the maximum electric field strength is 15kV/mm and 16.2kV/mm respectively. The curvature radius of the top shielding ring needs to be larger than that of other layers, after optimization, the maximum field strength is 2.68kV /mm when the curvature radius is 300mm. The internal insulation design of 200kV power supply transformer according to lightning impulse. The simulated and measured values of non-uniform voltage coefficient of 800kV power supply transformer under lightning impulse are 1.048 and 1.0488 respectively, in which the voltage equalizing capacitance is 3000pF. The insulation tests of 200kV and 800kV power supply transformer were all passed, and it can be operated safely. Effectively support the development of UHV DC circuit breaker.