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Air insulation strength relates closely to the electrostatic field distribution of the gap configuration. To achieve insulation prediction on the basis of electric field (EF) simulations, the spatial structure is characterized by a feature set including 38 parameters defined on a straight line between sphere electrodes. A support vector classifier (SVC) with particle swarm optimization (PSO) is used to establish a prediction model, whose input variables are those features. The EF nonuniform coefficient f of each sample gap is calculated and used for training sample selection according to the ranges off values. Trained by only 11-sample data, the PSO-optimized SVC model is employed to predict the power frequency breakdown voltages of 260-sphere gaps with a wide range of structure sizes. The predicted values coincide with the standard data given in IEC 60052 very well, with the same trend and minor relative errors. The MAPEs of the five predictions with different training sets are within 2.0%. The model is also effective to predict the breakdown voltages of Φ9.75-cm sphere-Φ6.5-cm sphere gaps, whose MAPEs are within 2.6%. The results demonstrate the effectiveness of the EF feature set and the generalization ability of the SVC model under the case of limited samples. This paper lays the foundation for estimating the dielectric strength of other air gaps with similar structures.

With the construction of 200 kV flexible DC power grid, 200 kV DC circuit breakers have been demanded. The fast mechanical switch, which is an important component in the hybrid DC circuit breaker, usually adopts multi-break structure to meet the requirements of breaking time and effective opening stroke. For a 200 kV double-break fast mechanical switch, the voltage characteristics in the breaking process were analyzed firstly. Then, the distributed capacitances' parameters were calculated by the finite element method. Finally, the voltage-sharing components' parameters were simulated by using PSCAD/EMTDC. It is suggested that the voltage-sharing capacitors' value be selected from 260 pF to 300 pF, 200 Ω for the current limiting resistor, and 200 MΩ for the voltage-sharing resistor. The research can provide a reference for the voltage-sharing design of mechanical switches in non-arc hybrid DC circuit breakers.

The distribution of electric field (EF) has a strong correlation with air insulation strength. In order to obtain air gap breakdown voltage (BV) through simulating calculation instead of experimental measurement, various parameters related to the electrostatic field distribution are used to characterize the sphere gap structure, which are defined on the shortest path between two sphere electrodes. These features of different sphere gaps are extracted from EF simulation results and input to a support vector machine (SVM) model optimized by the grid search algorithm, so as to establish their correlations with the output BVs. The golden section search method is used to predict the BV iteratively. Taking 9 sphere gaps, with the diameter in the range of 15 to 50 cm, as training samples, the SVM model is employed for BV prediction of 107 quasi-uniform sphere gaps with different diameters ranging from 75 to 150 cm and gap distances from 2 to 75 cm. For the predicted results, the average relative error is only 0.97% compared with the test values presented in IEC 60052. The results demonstrate the effectiveness of the EF features and the prediction model. This research offers a reference for air gap BV calculation by numerical approaches.

The hybrid high voltage direct current (HVDC) breaker is a key equipment of the DC grid. The high speed mechanical switch is a key component of the hybrid HVDC breaker and has a number of serially connected switch units. The serially connected units should divide the voltage uniformly. The static voltage distributions and distributed capacitances of a 500 kV hybrid HVDC breaker mechanical switch are studied in this paper. A three dimensional finite element model, considering the actual dimension parameters of six 110 kV high speed mechanical units in serially vertical arrangement, is established to study the static voltage distribution characteristics and capacitance parameters of a 500 kV multi-break high-speed mechanical switch, with six 110 kV high speed mechanical switches in serially vertical arrangement. The calculated results indicate that, under vertical arrangement, from the point of capacitive voltage distribution, the static voltage distributions of the six mechanical switch units are non-uniform, and the high voltage unit is more than 75% of the whole voltage.