Medium Voltage Cable Grid Operation Mode And Fault Model Simulation Analysis

With the city power grid development, more and more power cables used in medium voltage distribution network. Due to space and aesthetic needs, many of the city's distribution networks have all cables outlet. The increasing number of cable in distribution network, the capacitive current of the network is increasing. Some capacitive current of the network even more than a few hundred amperes. In recent years, many provinces progressively implement the strategy of economic circle. Major cities are in combination to create the region more competitive urban agglomerations. This makes the already growing distribution network current doubling after "hand in hand and the original operation mode will face a serious challenge.Most for medium voltage distribution network failures which remain in the mode of thinking mainly of overhead lines, cable lines, supplemented by. The proposed theoretical model for overhead lines do not apply to cable. This makes the cable's over-voltage and failure analysis difficult to avoid deviation. Therefore, it is great significance for the study a fault model applied to cable networks which is a highly representative object in medium voltage distribution network.Cable lines in the power system are distributed parameters of the circuit elements. The electromagnetic transient process of distributed parameter circuit belongs to the electromagnetic wave propagation process, referred to as the wave process. The formation of over-voltage in the transient process from propagates form the line to the end of the transformer, generator or transmission line and also spread from one line to another line connected in the form of waves. Each of the over-voltage cable lines can also be explained with wave process. Several typical voltage theoretical analysis for medium voltage cable network can provide a theoretical basis for the selection of the appropriate operating mode and simulation.Make improvements to intermittent arc ground theory which on the basis of the existing overhead lines and build the intermittent arc model suitable for medium voltage cable network; using a controlled switch turn-on and turn-off single-phase ground arc, and using variable resistor simulated arc resistance, to enable them to better reflect the dynamic characteristics of the arc. Make a study to cable insulation damage to combustion process. On the basis of theoretical studies, based on the intermittent arc model of cable to establish the arc burned model to consider the effect of heat accumulation. Using heat compared results to controlled the turn-on and turn-off of the arc grounding switch in order to achieve the transformation of the type of fault. This model fit the medium-pressure arc fault in the actual operation of the cable network more better.Combination of front theoretical analysis of medium voltage cable network over-voltage, applicant of PSCAD software simulation and combine with a different operating mode voltage simulation results compared. Pointed out that the neutral point grounding with via low resistance caused by the transient single-phase ground fault over-voltage limit best. And the most conducive to the protection system. Neutral via arc suppression coil grounding method for a variety of over-voltage can play a better role in limit, but not conducive to the protection system action.