Space charges accumulate easily at insulation interface of cable accessories, which cause different electric field distribution and aging characteristics compared to single-layered cable. To explore the space charge behavior in double-layered insulation of cable accessories, a one-dimensional (1D) axisymmetric model for bipolar charge transport is built in this work, in which the effects of temperature gradient and electric field gradient in the radial direction are considered. Then the influences of electric field/temperature gradient and interface position on transport behavior of space charges are investigated. The simulation results suggest that the charges accumulate easily at the interface, which severely reduce the electric field in the inner layer of insulation and further inhibit the injection and migration processes of charges. The charge density at the interface increases with temperature and voltage, which accelerates the decay of the charge injection, furthers the interface charges to reach the dynamic equilibrium state quickly. The charge density at the interface and the electric field distribution are closely related to the interface position, and the electric field is more uniform when XLPE occupies the 1/3 to 1/2 inner part of the whole insulation.INDEX TERMS Double-layered insulation, bipolar charge transport model, electric field gradient, temperature gradient, interface position.
The deep interdependence between electrical and natural gas system has great influence on the security of multi-carrier energy (MCE) systems. The large-scale access to distribution generation (DG) of clean energy makes it necessary to investigate the effects of uncertainties on the safe and stable operation of MCE systems. However, the existing probabilistic energy flow analysis for MCE systems pays little attention to the difference between the correlation of various DG during calculating the energy flow. Therefore, this paper investigates the probabilistic energy flow considering the uncertainties and correlations of various DG. A framework of MCE systems considering various coupling units including power to gas (P2G) and energy hub is initially proposed. For this, the Monte Carlo simulation (MCS) method based on Latin hypercube sampling (LHS) and Nataf transformation is specially designed to calculate the energy flow for each sample. The energy flow calculation method is composed of three-phase AC/DC alternating iteration method and improved Newton node mesh method considering the control mode of compressors. Finally, the test system containing improved IEEE123-node system and NGS48-node system have verified the accuracy of the proposed probabilistic energy flow calculation method. INDEX TERMS Renewable-based multi-carrier energy systems, energy hub, probabilistic energy flow, Nataf transformation, Monte Carlo simulation.
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