The type test of hybrid DC circuit breaker of Zhangbei project includes inter-terminal switching impulse voltage test. It is used to verify the insulation performance between the incoming and outgoing terminals of DC circuit breaker. The capacitor of transfer branch has the capacitance of several microfarads. The capacity of existing test equipment can not meet the requirements of end-to-end switching impulse test of DC circuit breaker. Therefore

an equivalent test method is proposed to verify the ability to withstand switching impulse voltage between end-to-end of the hybrid DC circuit breaker. Firstly

the structure of hybrid DC circuit breaker is analyzed to determine the equivalent test mode of main branch

transfer branch and energy dissipation branch. Secondly

the atmospheric correction coefficient is calculated

and the unequal voltage coefficient of the transfer branch is experimentally studied to determine the test voltage of the main branch

the transfer branch

and the energy dissipation branch. Finally

the test circuit is established and the corresponding equivalent tests are carried out. The connection mode of impulse generator capacitor and the selection of current limiting inductance value in the circuit are studied in the equivalent test circuit of transfer branch. The research results show that

（1）Inter-terminal dynamic insulation test of quick mechanical switch and inter-terminal switching impulse voltage test of single-layer transfer branch can replace the inter-terminal switching impulse voltage test of hybrid DC circuit breaker.（2）The altitude of Kangbao converter station with the highest altitude in Zhangbei project is 1 385 m

and the maximum atmospheric correction coefficient is 1.12. The maximum unequal voltage coefficient of the transfer branch is 1.015. The test voltage peak of quick mechanical switch is 1 031 kV

and the test voltage peak of single-layer transfer branch is 210 kV.（3）The best connection mode of impulse generator capacitor is 6 in parallel and 3 in series when inter-terminal switching impulse voltage test of the single-layer transfer branch is carried out. At this time

the requirements of single-stage capacitor charging voltage and the single-stage wave head resistance energy are minimum. The current limiting inductance in the circuit is selected as 0.5 mH. When the current limiting inductance is larger than 0.5 mH

the circuit will oscillate which resultes in voltage drop at the peak of the test voltage waveform on the sample.（4）The equivalent test results show that the insulation design between the terminals of 535 kV hybrid DC circuit breaker meets the requirements.