Document Type : Research Articles

Author

• Mohammad Ali Taghikhani

Department of Engineering, Imam Khomeini International University, Qazvin, Iran

Abstract

Protective relay in the transformer may accept inrush current as fault current, thus, distinguishing the inrush current from the internal fault current is important in transformers. To estimate the transformer inrush current, the extended Kalman filter (EKF) is applied in this paper. Therefore, three phase transformer initial inrush currents are estimated using the extended Kalman filter formulation and a nonlinear model is used to simulate inrush currents. Then, type of current, whether it is a fault or an inrush current, is determined by comparing this current and the current calculated from the transformer model. It is considered as a fault current, if the inrush current estimation error surpasses a certain limit compared to the transformer actual inrush current. On the other hand, connection of the winding to the ground fault location has been also presented in this paper which has been less investigated in previous studies. Also, the relation of the fault location to the estimation error standard deviation is also studied and an index  is introduced. If the value of this index is greater than a specific value in any phase of the transformer, a fault condition is identified. Finally, the proposed technique is implemented for another transformer to calculate the estimation error standard deviation and index  in the faulty condition. The results show the index β values are in agreement with the index limits and validate the accuracy of the proposed method.

Keywords

• Estimation
• Extended Kalman filter (EKF)
• Fault location
• Inrush current
• Standard deviation

Main Subjects

• Power systems