In this paper, grid connected DSTATCOM with three phase three wire has been proposed for harmonics elimination, reactive power compensation and active power injection into the grid. An improved instantaneous reactive power theory based on the least mean square is computed. The least mean square (LMS) algorithm is combined with instantaneous reactive power theory (IRPT) to improve its dynamics performance and eliminates the use of low pass filter requirement for computation of reference current. The harmonics component of the active power is estimated from LMS algorithm generated load harmonics currents. The performance characteristic of DSTATCOM is estimated with control scheme using computer simulation. The technique is based on the instantaneous transformation of instantaneous signals and taking advantage of the subsequent calculation of power from supply side to the loads. The neural network based method to estimate the harmonic online, DSTATCOM can compensate the harmonics. The computer simulation is carried out with MATLAB Simulink power system block sets.
This paper intends to detect the inter-turn fault by performing impulse test on HVDC Converter transformer by Coherence Function method. The inter-turn in a transformer (due to insulation failure) is located in impulse test by neutral current method. In the neutral current method, a record of the impulse current flowing through a resistive shunt between the neutral and ground point is used for detecting the fault. Neutral current so measured or calculated is in time domain. Theoretically the calculated neutral current, both for healthy winding and turn-fault winding is subjected to FFT to convert time domain into frequency domain of real and imaginary values. The real and imaginary values are used to calculate the coherence function. Coherence function compares both with and without fault neutral current in frequency domain, so that fault can be identified. Coherence function compares input and output at each frequency.It displays output i.e coherence value as 1 if input and output at that frequency is same other wise less than 1. 1 indicates that there is no fault at that frequency and decreasing coherence value (<1) indicates fault at that frequency.
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