When a hybrid HVDC circuit breaker operates normally

it can neither acquire energy from DC capacitor as in modular multi-level converter（MMC）

nor can it be directly energized by utilizing the electromagnetic coupling of AC system such as an electronic transformer in AC system. Consequently

according to the load characteristics of different components in 500 k V hybrid HVDC circuit breaker

a multi-objective and multi-level isolated power supply system scheme in power frequency is proposed to solve the problems and difficulty in power supply for different components of the hybrid HVDC circuit breaker under normal operation and during transient breaking process. The main solutions include isolation between layer and ground

between layers

and between valve groups. Regarding the most critical main power supply transformer which isolates the layer and the ground

the voltage sharing characteristics of multi-level series-connected transformers under transient and steady state conditions are studied

and the corresponding voltage sharing means are proposed at first. Then

the electromagnetic field

losses and temperature rise of the designed power supply transformer are analyzed by theoretical calculation and simulation. Finally

the proposed power supply system is tested and verified in 500 kV hybrid HVDC circuit breaker. The test results show that multi-objective power supply system according to the load characteristics of different components in the hybrid HVDC circuit breaker can significantly reduce the overall capacity requirements of the transformer

thus reducing the volume of the equipment and the difficulty of development. Meanwhile

multi-level isolation allows the reduction of the insulation level of single equipment

which is easy to achieve. By taking proper transient and steady-state voltage sharing measures

the proposed power supply transformer is able to meet the technical requirements of non-uniform coefficient of voltage less than 5%

lightning impulse voltage up to 1 550 kV

switching impulse voltage up to 1 300 kV

and internal temperature rise less than 40 K.