Rabindra Mohanty

This paper presents the fault direction identification and fault type classification in power electronic converter interfaced lines using time-domain signals in three-dimensional (3D) Cartesian coordinates. The protection issues with such lines are identified first, then the feasibility of the time-domain technique is highlighted. Since the current from the converter during fault gets modulated due to various control strategies, protection in such cases using conventional methods is a challenge. The concept of the dot product of 3D voltage vectors in Cartesian plane is proposed for fault type classification. The directions of the fault such as forward and reverse are inferred using the cosine of the angle difference between voltage and current vectors on 3D Cartesian plane. The performance of the proposed method is tested for different conditions in the modified CIGRE LV benchmark using PSCAD/EMTDC simulation. Using the real-time digital simulator (RTDS) and controller hardware-in-loop (CHIL), the performance of the proposed method is also validated and found accurate.

This article presents a backup protection scheme for hybrid ac–dc microgrids. A time-domain technique is proposed to isolate the faulted dc and ac subgrids from the point of common coupling using ac and dc currents, respectively, in case the primary protection fails. Symmetrical component decomposition in a bipolar dc microgrid is used to obtain the mode-0 and mode-1 current at the terminal of the bidirectional interlink converter (BIC). The superimposed component of mode-1 current acts as the decisive discriminator between ac and dc subgrid faults. One cycle moving average of the phase currents at the BIC terminal identifies the ground faults in dc subgrids. Further, the pole-to-pole faults in the dc grids can be detected using two consecutive zero-crossing widths in the phase currents at the ac terminal. The proposed protection scheme is validated on a hybrid ac–dc microgrid, simulated using a real-time digital simulator and a digital signal processor in a hardware-in-loop scenario for different faults on either side of the microgrid.

Accurate voltage phasor measurement is important for differ-ent applications in electric power systems including protection, control, and monitoring. At power transmission level, the transient response of the capacitor voltage transformer is a concern for the phasor based protection applications. This letter presents an accurate voltage phasor measurement technique at an electric bus during transient using the current through the capacitor voltage transformer. The numerical integration of current is multiplied with current transformer ratio and with the reciprocal of equivalent capacitance of the capacitor voltage transformer to obtain the accurate voltage during transient. The dependency of the obtained voltage accuracy on the current measurement error is also analyzed. The performance of the proposed technique for phasor estimation used in directional and distance protections during capacitor voltage transformer transient is demonstrated and found to be accurate. The performance of the proposed method is free from the capacitor voltage transformer topologies and operating conditions of electric power systems.

This article presents a unit protection scheme for bipolar dc microgrids, which is resilient to cyber attacks. The proposed method uses current measurement of both ends of the protected line segment for distinguishing the internal faults and cyber attacks. For any change in current, the disturbance index exceeds the threshold value, subsequently, the proposed protection algorithm is triggered. Being a bipolar dc system, the concept of symmetrical component decomposition is used to obtain the bias, unbalance, and balance components during an unbalance condition. The superimposed balance component of both ends of the line on a four-quadrant plane acts as a decisive discriminator between internal and external faults. The correct faulted pole is identified by analyzing the superimposed unbalanced component. By comparing the superimposed bias component with the local pole domain currents, the cyber attack is correctly identified. The proposed protection scheme is validated on a ring-type bipolar dc microgrid, simulated in real-time digital simulator, for different internal and external faults and cyber attacks. The performance of the proposed method is tested for various conditions, including the detection of internal and external high resistance faults, fault type classification, change in load, distinguishing between different faults, and cyber attacks. A comparative assessment of the proposed method with the available techniques confirms its strength.