الفهرس 
A SHORT SURVEY ON FAULT DETECTION IN POWER TRANSFORMEROnly 14 pages are availabe for public view
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Abstract
Power transformer is amongst the most important components in a power system.
Avoiding damage to power transformer is vital, other wise continuity in power
delivery may be seriously disrupted. Furthermore, repairing or replacement is
expensive and time consuming. So, the protection system of a power transformer
must be robust, discriminative and fast. The discrimination between an internal
fault and a magnetizing inrush current has long been recognized as a challenging
power transformer protection problem. Conventional protection systems are
designed to restrain during inrush transient phenomenon by sensing a large second
harmonic component. However, this component may also be generated during
internal faults due to current transformer saturation or the presence of shunt
capacitor or distributive capacitance of a long EHV transmission line to which the
transformer can be connected. in modern large power transformers, this harmonic
component in the magnetizing inrush current tends to be relatively small because of
the improvements of core materiaL Consequently, the commonly employed
conventional differential protection based on second harmonic restraint will thus
have difficulty in discrimination between inrush current and internal faults, thereby
threatening transformer stability. Alternatively, improved protection techniques for
accurately and efficiently discrimination between internal faults and inrush current
have to be thus found.
The wavelet transform is a relatively new and powerful tool in the analysis in
transient phenomenon because of its ability to extract information from the
transient signals simultaneously in both time and frequency domain, rather than
conventional Fourier transform which can only give the information in frequency
domain.
This work presents a novel technique based on wavelet analysis to design a
differential relay for power transformers. The designed relay is able to distinguish
between magnetizing inrush current, and internal fault currents. The (ATP) transient program is used to simulate study cases for power transformer in different
faulty conditions and normal operation. Daubichies Wavelet is. applied to analyze
the three phase differential current signals output from simulation program. The
outputs from wavelet analysis effectively trace the time evolution of various
frequency components of all signals, so it becomes easy to identify inrush and
other transformer faults. The extensive simulation studies have verified that the
proposed technique is more reliable, simpler, than conventional methods and is
suitable for different power transformers of various sizes and designs.