Sharif Digital Repository

Inrush current as an inherent phenomena in transformer energizing cause to dramatic increase in current which flow through windings of transformer in first periods of energizing. first peak of inrush current can exceed even to several orders of nominal current but it decrease with time and at last after damping process it reaches to nominal currents. In large transformer this time can exceed to several minutes and cause damage to winding insulation, mechanical defects, wrong response of protection system and interrupting loads. Magnitude of this current has a close relation with residual flux. In this thesis a method for calculation of inrush current in single phase and three phase... 

Inrush Current is a form of over-current that occurs during energization of a transformer. For power transformers, the magnitude of the first peak of inrush current is initially several times the rated load current but slowly decreases until it finally reaches the normal exciting current value. This process typically takes several minutes. Time-variant axial and radial electromagnetic forces under inrush current and short-circuit current are calculated (by finite element method; FEM), and compared. An analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this proposed method are compared with the measured values. A compact... 

One of the most critical equipments in power grids are power transformers, which are vulnerable to damage due to the possibility of faults in its various components. A very common category of such faults is turn-to-turn fault in its winding. This fault initiates by the aging of the winding insulation with a short circuit of several adjacent loops to each other and if it is not detected quickly by the transformer protection, it will spread rapidly and can lead to irreparable failure in the transformer. Traditionally, turn-to-turn fault should be detected by mechanical pressure relays, however, due to the poor performance of these relays in the rapid detection of this type of fault, in the... 

One of the special regimes of a wind turbine transformer operation is its repetitive connection and disconnection from the wind turbine (or the grid) via a short length of cable. Energizing the transformer will stress the transformer in two ways: the passage of inrush currents, and the initiation of possible high frequency resonances in the windings. In this thesis, first the 3D-wound core transformer design is investigated as a mean for reduction of the transformer inrush currents drawn from the grid. It is shown that this desirable performance is due to H-balance equation in this type of core and therefore the transformers of this type preserve a suitable response under energization to be...