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Most of the available directional relaying schemes use the phase angle information of sequence components of voltage and current with a cycle or more as the decision time. Converter interfaced solar photovoltaic plants are subjected to follow grid codes, leading to significant voltage and current modulation compared to conventional synchronous machines based sources. This may result in malfunction of existing directional relaying. This paper presents a high-speed time-domain directional relaying method using only phase fault current for distribution systems in the presence of solar plant. The method proposes a fault direction discrimination function, and its sign provides the direction of fault. The proposed method is tested for various control options embedded in solar plant, fault parameters, and noisy signals in CIGRE 14-bus distribution system integrating solar plant. Results validate the ability of the proposed method to decide within one-fourth of a cycle following fault detection for both PV plant side as well as grid end. Comparative assessment reveals the superiority of the proposed current based direction relaying method over the existing technique. [ABSTRACT FROM AUTHOR]

For fault ride-through requirement, solar photovoltaic (PV) plant remains connected to the grid during a fault. In such a situation, a PV plant operates in different modes and supplies current to comply with the requirements of the grid. The relative magnitude of phase current contributed by a PV plant during a fault is at par with the nominal current. Such a fault behavior restricts the application of available phase current based relaying approaches while protecting the distribution system with a PV plant. A protection method using local positive sequence voltage and current is proposed to protect a distribution system with PV plant. The method selects pickup current using proposed current-voltage curve for fault detection. A three-dimensional time-current-voltage characteristic is proposed for trip time calculation. Performance of the proposed method is tested for relays on both PV plant side and grid end using DigSilent PowerFactory simulation data for a CIGRE 14-bus distribution system with PV plant having different modes of operations. The method is found to be accurate and comparative assessment reveals its superiority. [ABSTRACT FROM AUTHOR]

Distribution lines are generally protected by overcurrent relays. With the integration of an inverter-interfaced solar photovoltaic (PV) plant having a current-limiting feature, the fault current seen by the relay on the PV side of that feeder becomes comparable to the load current. The conventional overcurrent relaying principle is not suitable for distribution line protection. Distance relay may be a viable option for protection of distribution lines connecting the solar PV plant. However, positive- and negative-sequence source impedances of the PV plant depend on an inverter controller, which results in limited performance of fixed setting distance relay. This article proposes an adaptive distance relay setting to protect distribution line connecting the PV plant, using prefault voltage and current data at the relaying point. The method calculates positive- and negative-sequence PV source impedances for boundary setting of distance relay at the PV side. The proposed trip boundary is modified adaptively with the change in prefault conditions of the PV plant. Performance of the proposed method is tested for different control strategies and operating capacities of the PV plant and variation in the grid source impedance on a 34-bus distribution system. Real-time application of the proposed method is validated in hardware-in-the-loop using OPAL-RT simulators with IEC 61850 as the communication protocol and found to be accurate. [ABSTRACT FROM AUTHOR]

As grid codes evolve, inverter-interfaced renewable generation may be required to take greater responsibility for grid support. It may be obliged to source a large current during a short-circuit fault in the grid and provide large dynamic reactive power, beyond the inverter rating, for voltage recovery after the fault clearance. In this sense, the inverter-interfaced generating system would behave more similarly to a conventional synchronous machine. This is not yet mandatory but current technology cannot readily support it if required in the future, because the power semiconductors would overheat unless they are drastically derated. This study proposes a method to increase the power semiconductor's transient thermal capacity, and hence its short-term over-current capability, by integrating a phase-change material inside the power semiconductor module. Experiment and thermodynamic simulation across different materials are used to illustrate the feasibility of the concept and the factors that should be considered in such a design. The study shows that 1.5 p.u. (per unit) overcurrent could be achieved for 30 s, which is typical of synchronous generators; and 3.0 p.u. fault current could be achieved for 3 s. A custom-made 1200-V, 50-A IGBT half-bridge module integrating a liquid metal as the phase change material is compared with a conventional commercially available module. A validated simulation model is then used to further evaluate the proposal, regarding a 1700-V, 1000-A IGBT module for use in a wind turbine. [ABSTRACT FROM AUTHOR]

This manuscript develops a unified control structure for Distributed Generation (DG) units based on Voltage Source Converters considering unbalanced and non-linear operating conditions. This control structure works for both the Islanded and the Grid-connected modes of operation of the Micro-Grid (MG). The objective of this control scheme is to regulate the line currents of the DG unit in such a manner that the voltage at the Point of Common Coupling (PCC) remains balanced despite the line currents of the DG unit being unbalanced and distorted. Multiple adaptive P-R controllers have been proposed for the current control loop of the Voltage Source Converter (VSC). These controllers have been implemented with resettable integrators so as to limit the DC components in the post fault current of the VSC. The Battery Energy Storage System (BESS) is interfaced to the DC link of the VSC through bi-directional dc-dc converters. An improved control structure for the bi-directional dc-dc converter has been developed. The effectiveness of these control structures have been presented and tested in PSCAD/EMTDC in an IEEE 34 node distribution system model being fed by two identical DG units. [ABSTRACT FROM AUTHOR]

Communication-assisted distance protection schemes are widely used for three-terminal line protection and are susceptible to power swings. The available differential protection scheme is also considered to be suited to protect three-terminal lines and is free from problems associated with the power swing. However, the performance of the current differential protection scheme may be affected if an outfeed condition occurs during an internal fault. This paper presents a new technique for protecting three-terminal transmission lines immune to power swing. The technique uses synchronized voltage and current measurements from three terminals for calculating voltage at the tee-point. The maximum magnitude of the superimposed component of positive-sequence voltage estimated at the tee-point is compared with the maximum magnitude of superimposed componentas of the positive-sequence voltage measured at three terminals of the line to discriminate a fault from power swing. The method is accurate even for an outfeed condition during the internal fault, current-transformer saturation during severe internal or external faults, large load rejection, and different prefault loading conditions occur during the power swing. The proposed algorithm is verified using data simulated through EMTDC/PSCAD for a 400-kV double-circuit three-terminal system. [ABSTRACT FROM AUTHOR]

Maloperation of the zone 3 element of distance relays during stressed system conditions, such as power swing, load encroachment, or voltage stressed condition is one of the main reasons for large disturbances in power systems. The improved protection technique for zone 3 can help to prevent such maloperation and, thus, more reliable power systems can be envisaged. This paper proposes an algorithm that utilizes two new criteria: 1) the maximum value of the transient monitoring function obtained from three-phase currents and 2) the phase angle of the positive-sequence impedance to support zone 3 of the distance relay. The technique is tested for various power system events, such as the three-phase fault during the power swing, load encroachment, voltage stressed conditions, and current-transformer saturation during the three-phase fault using data simulated through EMTDC/PSCAD in the IEEE 39-bus New England system. The simulation results show that the zone 3 protection scheme using the proposed technique can correctly discriminate the three-phase fault from stressed system conditions. [ABSTRACT FROM PUBLISHER]

This paper presents a synchronized phasor measurement-based wide-area backup protection scheme which compares the magnitude of sequence voltages of buses at a system protection center to identify the bus closest to the fault. Then, the sign of cosine of the angle between voltage and current at both ends of all lines connected to this bus are compared to identify the faulted branch. The technique is tested for various faults resulting in voltage/current inversion in a series-compensated line and during load encroachment and power swing conditions using data simulated through EMTDC/PSCAD for a nine-bus, three-machine power system. The scheme is found to be accurate and fast. With today's synchronized phasor measurement technology and communication system, the proposed scheme can overcome the limitations of the conventional backup protection scheme. [ABSTRACT FROM AUTHOR]