Medium Voltage Alternating Current System Grounding Circuit

Navy medium-voltage power systems use high-resistance grounding (HRG) to limit fault current and prevent overvoltages. Because of high losses (~80kW) in the resistor, HRGs are transiently rated or excessively large. This topic requests a grounding system that fulfills HRG functions with low loss and small footprint. We will analyze the following less-common grounding methods against a notional power system and select one or a combination of them for detailed design. Resonant grounding. The power system is grounded via variable inductance which is in series with the system’s parasitic line-to-ground capacitance and tuned to produce a series resonant circuit. Because line-to-ground capacitance will change with different plant lineups, the inductance must be variable. Methods of determining the capacitance and tuning the inductance will be explored.Pulsing grounding. This is an HRG system that, upon detection of a ground fault, goes into a “pulse” mode where the effective resistance is reduced via switching a resistor in parallel with the fixed HRG resistor, producing a pulsing ground current. Fault detection algorithms can be developed to detect this signature, enabling easier fault detection than typical HRGs. Resistor sizes and duty cycle could be tuned for inde?nite time operation. We will explore different resistor sizes and switching algorithms.Oversized HRG with switched surge protection devices. The HRG is oversized with respect to system capacitance with surge protective devices (SPD) used to mitigate potential overvoltages. The SPD may be undersized with respect to voltage rating and switched in upon a ground fault. Water resistor. Used in high-voltage pulsed-power systems, water resistors are used to absorb high energy at a high peak-to-average power. They consist of Tygon or polycarbonate enclosures with dionized water with an electrolyte solution mixed at a ratio that achieves the desired resistance. We will assess liquid resistor designs against the topic requirements.