Performance of transformer differential relay at different neutral grounding resistance based on wavelet transform

Abstract Power transformer protective relay should block
the tripping during magnetizing inrush and rapidly should
operate the tripping during internal faults. There are a variety
of protective relays using different measuring techniques
to provide reliable and secure transformer protection. These
types of the protective relays include electro-mechanical,
solid state, digital and numerical relays. Within each group
of them, various algorithms are existed. A stand-alone digital
relay has been designed and implemented, where its
function can be modified easily to accommodate the protection
of different types of transformers by only changing
its attendant software. This paper suggests a possibility of
improving the digital power transformer algorithm for the
protection of three-phase power transformers based on the
discrete wavelets transform. This algorithm is able to discriminate
between the inrush and internal fault currents even
in the case of an inrush with a low second harmonic component
and an internal fault current with a high second harmonic
component. A sample of a power transformer is simulated
using the Electro Magnetic Transient Program, and the generated
data are used by theMATLAB to test the performance
of the technique, such as its speed of response and reliability.
The obtained results showed that the proposed algorithm
is reliable, accurate and fast. Also in this paper, the performance
of the proposed algorithm is tested for different neutral

grounding resistances of the transformer, as it greatly affects
the relay sensitivity in the case of turn-to-ground fault.

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