Abstract: With more and more distributed energy resources (DERs) being installed, the utility requires these generation systems and their interface converters to remain grid connected during voltage sags to ensure the operating stability of the ac power system. These low-voltage ride-through (LVRT) requirements also suggest that the DER generation system injects real power and reactive power to support grid voltages. In this paper, a positive- and negative-sequence current injection method is proposed to meet the LVRT requirement. The proposed method imposes a predefined ampere constraint in its current injection to reduce the risk of overcurrent during the LVRT operation. Its operation principle and control method are explained and analyzed. Experimental results are presented to validate the effectiveness of the proposed method. Comparisons of the proposed method and other LVRT techniques are also presented.

Abstract: The increased penetration of wind power into utility grid brings challenges to power converter design in wind energy conversion systems (WECSs). Among all, low-voltage ride-through has been enforced in the field, which is one of the major challenges for WECS. It is necessary to design an integrated controller to protect the converter from overvoltage/overcurrent and to support the grid voltage during faults and recoveries. In this paper, a unified dc-link current control scheme for current-source-converter-based WECS is proposed. The controllers for generator- and grid-side converters are coordinated to provide fault ride-through capability. In normal operations, the proposed control scheme can also smooth the real power flow while keeping the fast dynamic performance of the dc-link current control. Simulation and experimental results are provided to verify the proposed control scheme.

Abstract: This study presents a new method to select the settings of directional overcurrent relays. First, a new selection criterion of pickup currents is adopted. It results in discrete pickup current values, which mitigate the selectivity constraints effect on the minimisation of time multiplier settings. Second, the selectivity constraint equations are classified into individual groups with respect to backup relays. When solving these systems of equations, the initial time multiplier settings are obtained. The initial values are then increased gradually to find the final solution for all of the constraint equations. The proposed method is tested for three networks: 8-bus system, IEEE 14-bus system and IEEE 30-bus system. Its performance is evaluated and compared with the linear and non-linear programming techniques.

Abstract: The connecting of distributed generation (DG) to the distribution network has numerous advantages. However, in the presence of DG some problems in coordination of protection devices will occur, due to changes in short-circuit levels at different points. Fault current limiter (FCL) is applied to limit the fault current levels and the effect of DGs on coordination of overcurrent (O/C) relays during the faults. The use of DG and FCL in distribution networks causes to some transient currents during fault conditions. Steady-state coordination methods do not result in accurate settings in such networks. A new method is proposed for coordination of O/C relays by considering the transient behaviour of the network. This method is based on the genetic algorithm and uses the dynamic model of O/C relays instead of the fixed characteristic curves. For this purpose, transient behaviour of DG and FCL are simulated and the relay operating status is calculated for all primary and backup relays to achieve the optimal settings of relays in transient condition. Simulations are carried out on a sample network and the results demonstrate that the method gives feasible and effective solutions for optimal coordination in the practical power system networks in comparison to the previous steady-state methods.

Abstract: In interconnected networks, it is impossible to satisfy all coordination constraints. Some methods have been proposed in the literature to determine the minimum break point set (MBPS) before the coordination procedure. In this paper, a new method is presented which coordinates overcurrent relays and simultaneously determines minimum unsatisfied constraints as broken constraints (BCs). For the implementation of this method, a new objective function (OF) is defined that also includes constraints with various weightings. These weightings determine the priority of constraints for being satisfied which are obtained by means of some expert rules. The expert rules of previous papers are modified and weighted to determine the priority of constraints. The genetic algorithm is used to optimize the OF that has an internal feedback for determining the minimum BCs considering coordination criterion. The effectiveness of the proposed technique is demonstrated by comparing the results of two sample networks with those obtained by using the recently developed techniques.

Abstract: Bidirectional solid-state circuit breakers (BDSSCBs) can replace mechanical fault protection devices in systems having bidirectional current flow through a single bus, for increased transition speed, functionality, and reliability. Silicon carbide, 1200-V, 0.1-cm2 JFETs were designed and fabricated for the BDSSCB application. A novel BDSSCB gate driver was developed for both self-triggered temperature-compensated over-current protection, and external triggering. Bidirectional 600-V, 60-A fault isolation was demonstrated in a transition time of approximately 10 μs with two packaged JFET modules, a bidirectional RCD snubber, and a series distribution bus inductance of 20 μH.

Abstract: A switching power-supply apparatus and a switching power supply circuit in which a feedback signal is input from a feedback circuit to a feedback terminal of a switching control IC includes a capacitor and a Zener diode connected between the feedback terminal and a ground terminal. The Zener diode is a selectively connected external circuit. A voltage of the feedback terminal during an overcurrent operation changes depending on whether or not the external circuit is present. A return/latch determination circuit detects the voltage of the feedback terminal to switch between an automatic return system and a latch system in an overcurrent operation state.

Abstract: A networked charging station for electric vehicles protects against overcurrent and ground fault conditions. Upon detecting an overcurrent condition or a ground fault condition, the networked charging station for electric vehicles de-energizes a charging point connection to prevent electric current from flowing between an electric vehicle and the networked charging station and suspends the charging session. The networked charging station clears the overcurrent condition or the ground fault condition upon receipt of an authorized request which is transmitted remotely. The authorized request can be received from the vehicle operator that is associated with the charging session or from an administrator of the charging station through a radio-frequency identifier (RFID) tag enabled device or through a text message or an email message. The networked charging station clears the overcurrent condition or the ground fault condition without a manual reset of a circuit breaker or a GFCI device respectively.

Abstract: .................................................................................................................................................. 2 Acknowledge .......................................................................................................................................... 3 List of Figures ......................................................................................................................................... 7 List of Tables ......................................................................................................................................... 11

Abstract: Coordination of overcurrent relays in a meshed distribution system is a challenge task for the protection engineers. Initially it was done manually. Linear and non-linear programming optimizing techniques are very frequently used for Coordination of overcurrent relays. Presently artificial intelligence is applied for optimal co-ordination of Overcurrent (OC) relays. This paper discusses application of genetic algorithm for optimal coordination of OC relays in a loops distribution system. Combination of primary and backup relay is chosen by using graph theory, to avoid misoperation of relays.

Abstract: Protection of a distribution network in the presence of distributed generators (DGs) using overcurrent relays is a challenging task because of the changes in fault current levels and reverse power flow. Specifically, in the presence of current limited converter interfaced DGs, overcurrent relays may fail to isolate the faulted section either in grid connected or islanded mode of operation. In this study, a new inverse-type relay is presented to protect a distribution network, which may have several DG connections. The new relay characteristic is designed based on the measured admittance of the protected line. The relay is capable of detecting faults under changing fault current levels. The relay performance is evaluated using PSCAD simulation and laboratory experiments.

Abstract: Protection of a distribution network in the presence of distributed generators (DGs) using overcurrent relays is a challenging task due to the changes in fault current levels and reverse power flow. Specifically, in the presence of current limited converter interfaced DGs, overcurrent relays may fail to isolate the faulted section either in grid connected or islanded mode of operation. In this paper, a new inverse type relay is presented to protect a distribution network, which may have several DG connections. The new relay characteristic is designed based on the measured admittance of the protected line. The relay is capable of detecting faults under changing fault current levels. The relay performance is evaluated using PSCAD simulation and laboratory experiments.

Abstract: Fault analysis in solar photovoltaic (PV) arrays is a fundamental task to protect PV modules from damages and to eliminate the risks of safety hazards. This paper examines two types of unique faults found in photovoltaic (PV) array installations that have not been studied in the literature. One is a fault that occurs under low irradiance conditions. In some circumstances, fault current protection devices are unable to detect certain types of faults so that the fault may remain hidden in the PV system, even after irradiance increases. The other type of fault occurs when a string of PV modules is reversely connected, caused by inappropriate installation. This fault type brings new challenges for overcurrent protection devices because of the high rating voltage requirement. In both cases, these unique PV faults may subsequently lead to unexpected safety hazards, reduced system efficiency and reduced reliability.

Abstract: The disconnection of distributed generators (DGs) from a distribution network for every abnormal condition drastically reduces the DG benefits and system reliability when DG penetration level is high. The DGs can be used to supply the load demand in the absence of grid supply if DGs are allowed to operate in islanded mode. In this paper, protection issues associated with disconnection of DGs are addressed in the context of a radial distribution feeder. Protection strategies are proposed to allow islanded operation and to restore the system performing auto-reclosing maintaining as many DG connections as possible. An overcurrent relay based protection scheme is proposed for a converter based DG connected radial feeder to operate either in grid-connected or islanded mode maximizing the DG benefits to customers. Moreover, an effective method is proposed to restore the system with DGs using auto-reclosers. The proposals are verified through PSCAD simulation and MATLAB calculations.

Abstract: This paper presents the use of curtailment to allow more wind or solar power to be connected to a distribution network when overcurrent or overvoltage set a limit. For four case studies, all based on measurements, the gain in produced energy is calculated. It is shown that the curtailment method has a large impact on this gain. The paper further discusses details of the curtailment algorithm and the communication needs as well as some further applications of curtailment.

Abstract: Though distributed generators (DGs) have significant economic and environmental benefits, increased penetration of DGs will impose significant technical barriers for the efficient and effective operation of bulk power systems. Increased fault current contribution and load flow changes are the major two impacts on utility systems, and these will affect existing protective relaying, especially overcurrent relays. To ensure safe and selective protection relay coordination, the impact of DGs should be taken into account when planning DG interconnection. This paper presents an introduction of DGs and an overview of the impacts of DGs on system protection relay coordination. Several protection issues are identified to study the requirements for protection in the presence of DGs are also discussed. Key words: Distributed generator (DG), protection coordination, distribution network, overcurrent relay.

Abstract: This paper describes a study to determine the optimal resistance of a superconducting fault current limiter (SFCL) connected to a wind-turbine generation system (WTGS) in series considering its protective coordination. The connection of the WTGS to the electric power grid may have serious effects on the stability and reliability of the overall system during a contingency due to the increase in fault currents. Moreover, it causes malfunction in the protective devices such as overcurrent relays (OCRs). To deal with this problem, the SFCL is applied to reduce the level of fault current increased by the connection of the WTGS. Then, to determine the optimal parameter of the SFCL, protective coordination between the existing multiple OCRs is considered based on the computation of fault current by the equivalent voltage source method. The effectiveness of the optimal resistance for the SFCL is evaluated by the time-domain simulation with the power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) software. The results show that protective coordination is well maintained without changing the previous settings of existing OCRs by applying the SFCL with its optimal parameter. Therefore, the system can keep its suitable reliability even when the level of fault current is increased by connecting the WTGS to the power system.

Abstract: Recently, microgrid operation increased significantly with increasing distributed renewable energy resources in the power system. Microgrids can operate with and without utility. Fault currents are significantly different in island and utility connected operation modes. Therefore, microgrid protection is one of the important subjects in microgrid operation. In this paper, a hybrid particle swarm optimization (HPSO) approach has been developed for coordination of directional overcurrent relays (DOCRs) in a microgrid system. The coordination constraints include the utility connected and an autonomous condition of the microgrid operation. In the optimization procedure, the current setting (Iset) of relays is considered as discrete parameters and time multiplier settings (TMS) is assumed as continues parameter. The proposed algorithm has two parts, in the first part, PSO is used to calculate the I set and in the second part, linear programming is applied to calculate the TMS of each relay. In the case study, loads connected to the network are divided into critical and noncritical ones. In normal operation of the system, distributed generators (DGs) operate in parallel with the utility. When a fault occurs on the utility side, noncritical loads are disconnected from the network and DGs are operated in microgrid as islanded mode. Regarding to simulation results, DOCRs have a suitable and reliable operation in both conditions of microgrid operations. In addition, overall operating time of the primary relays is properly minimized.

Abstract: The utility model discloses an LED lighting string circuit, comprising a rectifier, an integrated circuit and an LED lighting string connected serially in sequence. The LED lighting string circuit is accessed into an alternating current power supply in order to load rectified voltage on the LED lighting string. The integrated circuit comprises a plurality of drive switches; and each drive switch enables a corresponding short string in the LED lightening string to be shorted. When the voltage loaded on the LED lightening string is increased, the integrated circuit controls the drive switch so as to correspondingly increase the number of LED lamps through which electric current pass; and when the voltage loaded on the LED lightening string is reduced, the integrated circuit controls the drive switch so as to correspondingly reduce the number of LED lamps through which electric current pass. The electric currents of LED lightening strings are controlled so as to achieve better controls of circuit efficiency, reliability, anti-flashing feeling, voltage vibration, power factor, overvoltage, overcurrent, overheat, and the like.

Abstract: This paper presents optimal coordination of overcurrent relays by using artificial bees colony algorithm. The objective function of the relay coordination problem is to minimize the operation time of associated relays in the systems. The control variables used in this paper are the pickup current and time dial setting of relays. Quasi-Newton (BFGS), particle swarm optimization (PSO) and artificial bees colony (ABC) are employed to evaluate the search performance. For test, a 9-bus test power system was used. The simulation results showed that the artificial bees colony algorithm is capable to minimize the operation time of relays in the entire system. As a result, all search algorithms can solve optimal coordination relay which the artificial bees colony (ABC) gives the best solutions for coordination relay setting.

Abstract: In this paper, a gate drive using gate boosting and double-stage turn off including voltage clamping as well as with detection of overcurrent and a too high di/dt during turn on is discussed in detail. Besides the gate drive, also the design of a PCB-Rogowski coil, which is used for measuring currents and for di/dt detection, is explained and different designs are compared. The presented coil has a bandwidth of more than 28MHz and a propagation delay of 11 ns.

Abstract: A switching control IC outputs a rectangular wave signal from an output terminal thereof to a driving circuit. A feedback circuit compares a value of a divided voltage of a voltage across output terminals of a switching power supply device with a reference voltage, generates a feedback signal, and inputs the feedback signal into a feedback terminal of the switching control IC. A capacitor and a Zener diode are connected between the feedback terminal and a ground terminal. The Zener diode is selectively connected, and a voltage at the feedback terminal is changed in accordance with the presence of the Zener diode. A voltage at the feedback terminal is detected, and one of a latch method and a hiccup method is selected as a method for an overcurrent protection operation in accordance with the detected voltage.

Abstract: This paper describes the design of a digital over current relay (directional and non directional) and its performance on MATLAB/SIMULINK. Digital over current relays have advantages over electromechanical relays. Their fast, compact and reliable operation results in minimum outage of power system in case of fault. The paper also describes various data conversion steps involved in a digitization process. The logic based algorithm and developed relay model have been tested under various system dynamics and fault conditions. A 400V industrial distribution power system is used as a tutorial to simulate and test the performance results of the over-current relays, with motor start up inrush current consideration and backup relay coordination for safe and reliable operation. Similarly, a 132kV loop network is used as another tutorial example to simulate and test the directional performance of the over-current relay. For full paper, contact: Prof Muhammad Masood Rafi Editor, NED University Journal of Research Ph: +92 (21) 99261261-8 Ext: 2413; Fax: +92 (21) 99261255 Email: NED-Journal@neduet.edu.pk Website: http://www.neduet.edu.pk/NED-Journal

Abstract: The fault behavior of an inverter interfaced distributed generator (IIDG) is determined by its control, which is significantly different from a conventional generator. This paper examines in detail the key features of IIDG's fault behavior with respect to interference with distribution protection. As an example, the fault behavior of a commercially available photovoltaic converter is shown through a hardware-in-the-loop (HIL) simulation using real-time digital simulator (RTDS). A case study is then performed using the HIL setup to investigate the impact of IIDG on the recloser-fuse coordination in the fuse saving mode. The results illustrate that due to fault current limiting behavior of inverters, IIDG marginally impact primary and back-up protection in a distribution system. But with high penetration level, IIDGs may disturb the recloser-fuse coordination.

Abstract: The current accuracy and power efficiency of a boost white light-emitting-diode (WLED) driver are usually design tradeoffs since the power efficiency is inversely proportional to the reference voltage, whereas the current accuracy is proportional to the reference voltage. Traditionally, a boost WLED driver with high current accuracy and high power efficiency demand a large chip area because mismatch decreases with increasing size. This paper proposes an offset calibration technique to improve both current accuracy and power efficiency while keeping the chip area relatively small. An overvoltage protection (OVP) circuit and an overcurrent protection (OCP) circuit prevent the proposed driver from being damaged due to WLED failure. The design is fabricated in a Taiwan Semiconductor Manufacturing Company 0.25-μm 60-V bipolar-CMOS-double-diffused-MOS process. The measurement results show that the current variation is less than 1% when the input voltage and the number of loaded WLEDs are varied in a wide range. The maximum power conversion efficiency is 86.7% at a 5-V input with four loaded WLEDs. The OVP is 58 V, and the OCP is 2 A.

Abstract: Thermal issues shorten motor life. However, being too conservative on thermal limits decreases motor productivity. An Institute of Electrical and Electronics Engineers 49 thermal element creates a realistic thermal model of the motor because the element takes the load level and negative-sequence currents into account. The 49 thermal element is superior to older methods using inverse-time overcurrent elements (51). This paper discusses updates in the existing 49 thermal model implementation. Also discussed are resistive temperature detector biasing, resistive temperature detector voting and the role of transducers in the modern motor relay

Abstract: PROBLEM TO BE SOLVED: To provide a technique which can quickly determine the interphase short circuit of a brushless motor and also perform a steering assist control continuously even if the interphase short circuit occurs. SOLUTION: This electric power steering device includes: an interphase short circuit determination part which determines that the short circuit occurs in a control unit 51 when determining that a phase current is brought into an oscillating state in which the state of the overcurrent due to a predetermined short circuit and the state of the overcurrent due to a predetermined regeneration are alternately repeated; and a steering assist control unit which detects a phase in which the interphase short circuit occurs based on the results determined by the interphase short circuit determination part, suppresses the occurrence of overcurrent in a switching element connected to the phase in which the interphase short circuit occurs by restricting the duty of the switching element, and continuously performs the steering assist control. COPYRIGHT: (C)2011,JPO&INPIT