A.K. AL-Othman and K.M. EL-Naggar (Kuwait)
Transformer inrush, harmonics, estimation, protection.
This paper presents a new method to identify the inrush and fault currents for transformer protection. When a power transformer is energized, the resulting inrush current can cause a false tripping of protection system. The second harmonic contents of the inrush current is used to differentiate between the inrush and the fault situations. Estimation of the contents of the current signal is achieved using a fast and new algorithm. The main advantage of the proposed technique is its ability in producing the estimates in a very short time and at a very high degree of accuracy. The algorithm uses sets of digital samples of the distorted waveforms of the inrush and fault currents to extract the features of the signals. A simple expert system is then used to evaluate the results in order to differentiate between different situations. The proposed technique has been tested using simulated power system. The extensive simulation studies have indicated that the restrain signal can be issued in less than a quarter of the cycle, therefore the method can be used as an effective tool for high speed digital relaying.
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