Nowadays industrial processes are largely based on electronic devices such as programmable logic controllers and adjustable speed drives. Consequently, industrial equipments became less tolerant towards power supply disturbances. Voltage dips due to faults are surely among the worst disturbances for industrial equipments. A paper machine can be affected by disturbances of only 10% voltage drop lasting for 100 ms. A voltage dip of 75% (of the nominal voltage) with a duration shorter than 100 ms results in material loss in the range of thousands of US Dollars for semiconductors industry [1]. The high costs associated with these disturbances explain the increasing interest towards voltage dip mitigation techniques. The different mitigation methods comprehend both interventions on the power system (reducing the number of faults, reducing the fault clearing time, improving system design) and the use of mitigation devices such as static Transfer Switch (STS), Dynamic Voltage Restorer (DVR) and Uninterruptible Power Supply (UPS) [2]. The paper aims to present the Fault Decoupling Device (FDD) as a new possible means to mitigate voltage dips. In particular the paper investigates the performances of the device in case of unbalanced and multiple faults. The principle of operation is shown as well as some results carried out simulating a distribution system by means of the Matlab. It will also be shown that the use of the FDD allows to reduce fault currents, reducing thermal and electrodynamics stresses of equipment during faults. This effect is particularly welcomed, considering the increase in fault currents levels due to the large concentration of generation plants on distribution networks foreseen in the next years.
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