Research On Neutral Grounding Pattern And Over-voltage Of Vessel Power System Medium Voltage Network

The neutral grounding of power system is a comprehensive subject, the correct choice of grounding has an increasingly important practical significance. Because it directly affects the reliability, the insulation level of lines and equipment, relay protection,communication and electromagnetic interference of signal system.Recent years, ship load is increasing, the use of medium voltage power system is more widely. Conventional 440V power system is used in ship ungrounded way, this kind of grounding in a single phase ground fault occurred may have stable or intermittent arc, is not conducive to suppress system's over-voltage, In the medium voltage power system of ship, the high voltage generators are more widely used, in particular the extensive use of cable lines, making the system a significant increase in capacitive current, over voltage and resonant grounding arc over-voltage problem become serious, and the insulation requirement of high-voltage generator is very high, it is clear that the traditional ungrounded operation method is no longer suitable for medium voltage power systems in the ship, chosing a suitable neutral grounding method for medium voltage power systems is essential.In this thesis, the internal over-voltage from the power system point of view, to seek a reasonable way of neutral grounding. The main work includes:Introduction to several neutral grounding methods of common power system, from the scope of economic and other aspects of a comprehensive comparison. Ships introduced in the framework of power system voltage and internal over-voltage problems; in PSCAD/ EMTDC simulation model created to determine the model of the transformer, the line model and identify key model parameters. In high impedance earthed neutral point corresponding simulation systems, in accordance with the existing system parameters, calculated by the appropriate theoretical grounding resistor, determine the ground parameters. Provide a theoretical grounding reference for the grounding equipment's selection of the medium voltage power system of ship; of magnetic resonance in voltage simulation. Ferroresonance over-voltage has many different types, mainly simulation analysis on the PT resonance over-voltage and overcurrent disconnection. At three different neutral grounding modes (Neutral, Neutral arc suppression coil grounding, high resistance grounding the neutral point) for simulation analysis. From the simulation results, the high resistance grounding the neutral point can be quickly and effectively inhibit the PT resonance over-voltage and disconnection over-voltage; on the ground over-voltage arc is simulated. In actual operation, mainly intermittent arc earth over-voltage, so this is only for the intermittent arc overvoltage to simulation. Above the actual operation of the data, theoretical analysis based on frequency over-voltage closer to the actual values, so this model in the frequency arc to build a typical model. At three different neutral grounding modes (Neutral, Neutral arc suppression coil grounding, high resistance grounding the neutral point) for simulation analysis. From the simulation results, the mode of grounding with high resistance can be quickly and effectively discharge energy of the system, making difficult to re-ignite the arc, on the ground over-voltage arc significantly inhibited.Combined with the research paper, neutral grounding with high resistance is suitable for the medium voltage power system of ship.This method of neutral grounding could effectively control the system voltage, control the fault current within the allowable range, ensure power supply reliability, minimize insulation accidents, is an ideal neutral grounding method.