✔ low power losses during normal operation, resulting from use of fewer power semiconductor devices in the main branch (six FBSms form a 2 × 3 matrix, cooling system, and power adapter) ✔ use of a lightweight contact system (six Vis in series; 40.5 kV because each uFD separates without experiencing current) ✔ modular design (four modular units, 50 kV each; 36 FBSms in each unit), which facilitates maintenance and replacement of parts ✔ high reliability resulting from exposure to lower voltages due to a series design that distributes voltages during switching. Because no relevant international electrotechnical commission (iec) standards currently exist, conformance tests had to be performed to verify the hVdc cB design. these were developed based on the operating principles and conditions of the hVdc breaker as well as the present iec standard for testing VSc hVdc valves. the test was divided into two parts: the insulation test and the operating test. the insulation test verifies the voltage-withstanding capacity and the voltage-sharing characteristic of an hVdc cB. the operating test checks the capacity of each core component to withstand serious stress and the operational properties under different circumstances. table 1 shows some of the main testing considerations. the 200-kV hybrid dc cB passed the test in which a 15-ka short circuit current was cleared within 3 ms and the transient interruption voltage across the test object exceeded 320 kV. Auxiliary Branch iT1 Ultrafast Disconnector Auxiliary Branch FBSM Main Branch iT2 FBSM FBSM Modular Unit FBSM FBSM Modular Unit FBSM FBSM Modular Unit FBSM FBSM Modular Unit Energy Absorber Main Branch iabsorb Energy Absorber uDB (a) (b) figure 7. (a) The topology and (b) a prototype of a 200-kV hybrid HVdc CB. table 1. Factors related to testing the insulation and operating characteristics of HVdc CBs. Number Test Test Object Items Objective 1 Insulation test Phases to ground DC voltage withstand test To verify the voltage-withstanding capacity and partial-discharge level of support structure 2 Switching impulse withstand test 3 Lightning impulse withstand test 4 5 6 Operating test Across open contacts DC voltage withstand test Key components Peak withstand current test Switching impulse withstand test 7 Overload withstand current test 8 Short-time withstand current test 9 10 To verify the current-withstanding capacitor of the CB Short-time withstand current test Overall prototype Rated current-interruption test 11 Short circuit current-interruption test 12 Rated current-making test 13 Short circuit-making test may/june 2019 To verify the voltage-withstanding capacity across open contacts To verify the current-interruption capacity and interruption time of the overall prototype and the program correctness of the control and protection system ieee power & energy magazine 91