• Energy Research

Quadrilateral characteristics of distance relays are widely used in modern power systems because of its lesser sensitivity to the variation in operating scenarios and fault parameters. The performance of quadrilateral relay is heavily dependent on the proper selection of reach settings. The reach accuracy of distance relays with settings estimated using conventional techniques deteriorates during stressed conditions such as load variation, power swings and remote end infeed/outfeed variations. A proper setting in addition to avoiding overreach and underreach cases should also posses higher loadability limit. In this regard, the relay reach setting has been mathematically formulated as a constrained optimization problem in the present work, with the aim of maintaining the trade-off between the reach accuracy and the loadability limit in terms of area enclosed by the relay characteristics. Sine–cosine algorithm has been adopted to solve the multiobjective optimization problem and hence obtain the reach setting of the quadrilateral relay. The performance of the proposed scheme in terms of providing optimal reach setting has been extensively examined against wide variation in fault parameters and operating scenarios. Further, in order to test the effectiveness of the proposed scheme for real-time applications, the suitability of the quadrilateral relay has also been validated by performing real-time simulations using OPAL-RT digital simulator.

Abstract DC microgrids have received wide interest in recent times because of the advantages related to improved power transfer capability, high efficiency, compatibility with distributed energy resources (DER) and reduced losses. However, the adoption of DC microgrids has been restricted because of the challenges in designing a reliable protection scheme. The challenge results from the high magnitude of the fault current without zero crossing, coupled with the requirement of high rapidity in fault detection. The scenario is further complicated during the variation in operational dynamics of microgrid either due to weather intermittency or network reconfiguration arising out of DER outage. Non-addressal of the above issues results in reduced grid resilience because of possible relay malfunction during stressed scenarios. In this regard, an ensemble classifier-based protection scheme has been proposed for DC microgrid with adaptability to system reconfiguration and weather intermittency. The adaptiveness has been achieved by online identification of network topology, while immunity to weather variation is attained by stochastic modelling of solar irradiance and wind speed. The use of local information for executing the protection tasks avoids the issues related to data loss and latency in the communication link. The task of operating mode detection, topology identification, fault detection/classification and section identification have been formulated as a set of classification problems and further solved using a random subspace sampling-based ensemble classifier technique. The reliability of the proposed scheme has been extensively validated for a wide range of fault scenarios involving wide variation in network topology, weather condition and fault parameters.

Abstract A low cost, fast and reliable microcontroller based protection scheme using wavelet transform and artificial neural network has been proposed and its effectiveness evaluated in real time. The proposed scheme, based on the hardware co-simulation approach performs all the functions of transmission line protection i.e. fault detection/classification, fault zone/section identification and location estimation. The fault detection/classification and zone identification algorithms use fundamental frequency current component to estimate a fault index. The fault location estimation module uses wavelet transform coefficients in hybridization with a parallel artificial neural network structure. For hardware implementation, a 8-bit ATmega microcontroller is used and interfaced with the simulated power system model using Integrated Development Environment (IDE). The scheme is tested on a power system model of 400 kV, 50 Hz three phase double circuit line with source at both the ends. Laboratory tests have been performed in real time for 20,000 fault cases including evolving faults with varying fault resistance, fault inception angle, fault distance, direction of power flow angle and its magnitude. The tests confirm the suitability and reliability of proposed scheme even with Current Transformer (CT) saturation. The implementation of the proposed approach on a low cost microcontroller with the lesser execution time, makes the prototype ideal for implementation on a digital platform (digital relay), thus leading to financial viability and sustainability of the protection scheme.