Analytical approach to internal fault simulation in power transformers based on fault-related incremental currents

A new method for simulating faulted transformers is presented in this paper. Unlike other methods proposed in the literature, this method uses the data obtained from any sound transformer simulation to obtain the damaged condition by simply adding a set of calculated currents. These currents are obtained from the definition of the fault. The model is fully based on determining the incremental values exhibited by the currents in phases and lines from the prefault to the postfault condition. As a consequence, data obtained from simulation of the sound transformer may be readily used to define the damaged condition. The model is described for light and severe faults, introducing this latter feature as a further add-on feature to the low-level faults simulation. The technique avoids the use of complex routines and procedures devoted to specially simulate the internal fault. Of prompt application to relay testing, the proposed analytical model also gives an insight into the fault nature by means of the investigation of symmetrical components. In contrast with its low complexity, the method has shown to present large accuracy for simulating the fault performance.