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Research Publications (Engineering and Built Environment)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/215

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Author: search.filters.author.Ngema, PhilaniHas files: Yes

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    Performance evaluation of percentage differential relays on power transformer and reliability assesment in HVDC grid protection scheme
    (IEEE, 2022-08-22) Ngema, Philani; Davidson, Innocent Ewaen; Buraimoh, Elutunji
    Percentage differential relays remain the most sensitive protection tool applied as backup protection on power transformers, busbar, and generators. Relays sometimes do mis-operate with the current transformer being affected by external fault leading to saturation, and the subsidence current present after clearing external faults. The cause of misoperation of percentage differential relays cannot be ignored that it entirely depends on magnitudes more than directionality for tripping decisions. This paper covers evaluating differential element performance, analysis of transformer inrush current, internal faults, external faults, and overexcitation conditions. The accurate computing of current transformers is also included. This protection only applies to 10MVA and above on transformers; however, it is not limited to transformers, but also transmission lines, busbars, and generators. The balance of the paper is on reliability assessment based on the HVDC grid protection scheme operation
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    A new technique for improvement differential relay performance in power transformers
    (IEEE, 2022-01-25) Ngema, Philani; Buraimoh, Elutunji; Davidson, Innocent
    Transformer protection devices are often used to identify internal or external transformer problems and act to either prevent damage or unnecessarily disconnect power transformers. This study proposes a new differential element that combines harmonic restraint, security, and reliability with harmonic blocking speed to improve the relay performance in a power transformer. Under high load, a negative-sequence differential element adds more sensitivity for internal turn-to-turn failures. External fault detection monitoring enhances security in an external problem involving current transformer (CT) saturation. Furthermore, overcurrent elements may be configured to vary dynamically in operation is provided. This element enhances protection coordination for various operating conditions without requiring modifications to the transformer group settings. The balance of the paper discusses the use of an under-load tap changer using a time-synchronized phasor monitoring system to reduce loop current and losses in parallel transformer applications.