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SUMMARYElectrical type tests are a key step to verify the design of voltage source converter valves for a specific modular multilevel converter (MMC) high-voltage direct current (HVDC) project. For a high-power handling capability of modern insulated gate bipolar transistor (IGBT), it is very difficult to balance between type test quality and test rig investment. In compliance with IEC 62501 and CIGRE 447 requirement, this paper presents a kind of synthetic test circuits (STCs), consisting of a steady-state test circuit, an IGBT overcurrent turn-off test circuit, and a short-circuit current test circuit, used for operational tests on MMC-based IGBT valve sections. Using the STCs, the current stress, the voltage stress, the junction temperature, di/dt, the performance of the valve's electronic circuits, and the protection capability of the parallel thyristor can be validated. Further, the parameters of the test circuits can be adjusted with the number of submodules of the MMC test valve. Thus, the STCs are an economical alternative for testing a representative part of an MMC valve. The paper describes and discusses the type tests, completely performed with the three test circuits, on MMC valves for a Xiamen MMC HVDC scheme, which is rated at 1000 MW/±320 kV. Copyright

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In this study, an equipotential shielding voltage sensor is proposed to achieve contact measurement of transient voltage in extra‐high voltage (EHV)/ultra‐high voltage (UHV) power grids. Two design versions of the voltage sensor for engineering application are described. One version of the sensor is designed as a miniaturized sensor for non‐disturbing measurement of potential distribution along power electronic equipment under transient voltage. The other version is designed for online measurement and monitoring in alternating current EHV/UHV power grids. Based on the design parameters, the performance of the sensor is evaluated, including stability of measurement, shielding effect against the interference from adjacent objects and frequency bandwidth. In order to verify the performance of this sensor, an experimental comparison between this sensor and a standard capacitive voltage divider used in high voltage laboratory was carried out and the results of comparison are presented. The results show that the difference of measured peak voltage between the two devices is no more than ±5%, and the difference of measured time parameters between the two devices is no more than ±15%.

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