In the multi-terminal flexible DC transmission system

installing DC circuit breaker is the most effective technical method to suppress the spread of fault current and ensure the safe

stable and reliable operation of a DC grid. The DC breaker power supply system plays an important role in isolating high voltages and powering modular operation and control components. Consequently

we researched the power supply system design of coupled negative voltage DC circuit breaker for Zhangbei Engineering Kangbao Converter Station. Firstly

the overall design scheme of the power supply system of the coupled negative voltage DC circuit breaker was elaborated. Uninterrupted power supply was achieved by using uninterruptible power supply（UPS） and switchgear

and the main branch and transfer branch isolated power supply were realized by three voltage level isolation transformers. The reliability of the energy supply system was improved by limiting surge current through soft-start of switchgear and paralleling surge protector and capacitor on output side of power supply transformer. Finally

the power supply system was tested with the DC circuit breaker prototype for insulation tests and operation tests. All the tests pass smoothly and the energy supply system works stably

which proves the rationality and reliability of the design.