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Protection of ungrounded systems using an advanced relay element

Siyambalapitiyage, Berty (2010) Protection of ungrounded systems using an advanced relay element. Other thesis, Murdoch University.

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    Abstract

    The aim of this thesis project is to investigate single line to ground faults in an ungrounded system and determine an effective fault detection method. Ungrounded system analysis is conducted using ICAP simulation.

    The fault detection method is focused on three different parts. The first part is used to identify the faulted feeder. Second part is for identifying the faulted phase and the last part is for estimating the fault distance.

    After simulating the model of an ungrounded system using ICAP, it can be observed that when a ground fault is present, the voltage magnitude of the unfaulted phase increases. The second observation is that when the fault is present, a zero-sequence voltage and a zero-sequence current are created in the ungrounded system. Therefore zero-sequence components can be used to identify the faults in an ungrounded system.

    A direction element is used to identify the faulted feeder of an ungrounded system. The relay measures the zero-sequence voltage (3Vo) and zero-sequence current (3Io) using a broken delta transformer and a current transformer. The relay calculates impedance (Vo/Io), If this impedance value is above the forward threshold then a directional element identifies it as a forward fault.

    The simulation result proves the above method and also shows the faulted feeder zero-sequence current lagging the voltage by 90 degrees and the unfaulted feeder zero-sequence current leads the voltage by 90 degrees.

    The phase difference between the positive sequence voltage (V1A) of one of the phases and zero-sequence current are used to detect a single line to ground fault on that phase.

    The simulation results show the above method is able to identify the faulted phase.

    In the final section, the simulation results show the magnitude of the zero-sequence current change according to the faulted distance therefore the single line to ground fault detection algorithm can use this characteristic to measure the fault distance.

    Publication Type: Thesis (Other)
    Murdoch Affiliation: School of Engineering and Energy
    Supervisor: Crebbin, Gregory
    URI: http://researchrepository.murdoch.edu.au/id/eprint/4066
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