Overcurrent Scheme Research Articles

OPTIMAL LOCATION AND SIZING OF DG IN DISTRIBUTION NETWORK: IMPACT ON OVERCURRENT DISTRIBUTION PROTECTION SCHEME

The integration of distributed generation (DG) into the existing distribution networks minimizes active power losses and improves the voltage profile. The recent improvement in the development of DG technology has caused increase in the penetration of DG from different sources. The optimal location and sizing of DG is very challenging and introduces different protection issues. This is caused by penetration of current flow from different source which is contrary to the principles of operation of the conventional overcurrent scheme. This paper presents optimal method of DG placement and sizing using firefly algorithm and its impact of DG penetration on overcurrent protection scheme. Low voltage distribution network is modelled and simulated in PSCAD/EMTDC and DigSilent power factory software using IEEE 33 and Ayepe 34 standard bus. False tripping of feeders, Nuisance tripping, blinding of the protection scheme and unintentional islanding caused as result of Photovoltaic penetration into the distribution network were simulated. Coordination of overcurrent relays with and without DG penetration were analyzed and possible mitigation algorithm were proposed. The simulation result obtained showed that the proposed methods significantly improve the protection scheme coordination..

Communication-less adaptive directional overcurrent protection strategy considering islanded mode detection in active distribution networks

The integration of distributed energy resources (DERs) in electric distribution networks originates the Active Distribution Networks (ADNs). The presence of DERs introduces challenges to conventional protection schemes due to bidirectional power flows and variations in fault current magnitudes; furthermore, the connection and disconnection of DERs result in multiple ADN operating modes (OMs), deteriorating the effective operation of protective relays. Considering the above, this document presents an adaptive protection strategy to address the challenges related to the variable nature of the ADN operation. The main contribution of the proposed approach is accurate islanded mode detection without requiring communication links, enabling fault detection in all ADN operating modes. The protection strategy maintains directional overcurrent relays' coordination using local voltage and current measurements to continuously estimate the Thevenin equivalent, fault currents, and adaptive coefficients.Relay coordination is maintained through tests conducted on a modified IEEE 34-bus feeder, considering several OMs, fault types, and locations. A comparison between the proposed adaptive protection strategy and a conventional overcurrent scheme shows that relay operating time is better in 100% of the analysed cases for the former strategy. On the other hand, the maximum errors in the fault current estimation using the Thevenin equivalent parameters are between 0.05% to 2.6% for all of the analysed operating modes when compared with the true fault current magnitudes. Finally, the adequate results validate the potential of the proposed communication-less protection strategy for modern protective relaying applications.

Application of Time-Voltage Characteristics in Overcurrent Scheme to Reduce Arc-Flash Incident Energy for Safety and Reliability of Microgrid Protection

The interconnection between diverse Distribution Generations (DGs) that utilize various technologies and complex structure of networks are the most characteristic of modern Distribution Networks (DN). The wide adoption of DGs considerably affects the power flow dynamics in the DN and consequently the fault characteristics. The excessive level of fault currents can pose risks of heat (high temperature) and pressure in accordance to Arc Flash (AF) incident energy in microgrids. This research studies the relationship between AF severity and the solving of coordination problem of Overcurrent Relays (OCRs) in DN, and introduces a novel equation that considers the AF qualities in solving the coordination problem for OCRs. In this study, a novel optimization problem, the AF severity with the optimal coordination of OCRs in DN is presented and the Water Cycle Optimization Method (WCOM) is employed to find the best combination of the OCR’s settings in the DN while considering the AF induced energy. The proposed optimization approach and the novel equation are evaluated with an IEC microgrid and compared with the conventional protection method and Particle Swarm Optimization (PSO) used in optimizing the coordination of OCR in the DN. The optimal settings of the OCR scheme are achieved and examined on the modified IEC microgrid benchmark system. In order to verify the result, an industrial simulation package (ETAP) and OCR (GE Multiin, model-750/760) was used in this work.

IEC61850 standard-based harmonic blocking scheme for power transformers

Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.

A novel constraint and non‐standard characteristics for optimal over‐current relays coordination to enhance microgrid protection scheme

Over the last few decades, the inverse over-current protection scheme has been one of the most common schemes utilised in protecting the distribution networks (DNs). Although over-current relays (OCRs) give an excellent protection in extreme failure situations, but continuous integration of distributed generation (DG) and the multi-looped structure of modern DN has made it difficult for the existing industrial OCR's to secure suitable coordination between the different OCR's. The problem of coordinating over-current schemes in the presence of DG needs a complementary between the optimisation techniques employed and the limitation of the manufactured relays existed in the DN for proper discrimination between OCRs. This study investigates the influence of excessive fault current due to DG penetration on conventional IEC characteristics. A novel constraint had been proposed to be added to the formula of the coordination problem – taking into consideration – the limitation of conventional IEC tripping characteristics utilised in nowadays numerical relays. Furthermore, a new non-standard tripping characteristic is suggested to increase the applicability of the optimisation techniques with the existing OCR's. A benchmark IEC microgrid is implemented in ETAP Package. The genetic algorithm is employed to investigate the effectiveness of the two proposed approaches to the conventional optimisation techniques in different operational modes.

Investigating the effect of DG infeed on the effective cover of distance protection scheme in mixed-MV distribution network

The environmental and economic features of renewable energy sources have made it possible to be integrated as Distributed Generation (DG) units in distribution networks and to be widely utilized in modern distribution systems. The intermittent nature of renewable energy sources, altering operational conditions, and the complex topology of active distribution networks makes the level of fault currents significantly variable. Thus, the use of distance protection scheme instead of conventional overcurrent schemes offers an appropriate alternative for protection of modern distribution networks. In this study, the effect of integrating multiple DG units on the effective cover of distance protection schemes and the coordination between various relays in the network was studied and investigated in radiology and meshed operational topologies. Also, in cases of islanded and grid-connected modes. An adaptive distance scheme has been proposed for adequate planning of protection schemes to protect complex networks with multiple distribution sources. The simplified simulated network implemented in NEPLAN represents a benchmark IEC microgrid. The comprehensive results show an effective protection measure for secured microgrid operation.Article History: Received October 18th 2017; Received in revised form May 17th 2018; Accepted July 8th 2018; Available onlineHow to Cite This Article: Saad, S.M., Naily, N.E. and Mohamed, F.A. (2018). Investigating the Effect of DG Infeed on the Effective Cover of Distance Protection Scheme in Mixed-MV Distribution Network. International Journal of Renewable Energy Development, 7(3), 223-231.https://doi.org/10.14710/ijred.7.3.223-231

Fully integrated high‐efficiency high step‐down ratio DC–DC buck converter with predictive over‐current protection scheme

A high-efficiency fully integrated 36 V–3 A stepping down DC–DC converter with high step-down ratio and predictive over-current protection scheme is introduced. To achieve high-voltage conversion ratio, emulated current mode and dedicated current sensing circuits were involved. A novel predictive over-current scheme is proposed to overcome inherent lack of emulated current-mode control and provide fast response to over-current events. In addition, due to N-type field effect transistor (NFET) was adopted to improve efficiency, a floating rail regulator is presented to generate bootstrapped voltage for driver stage. The proposed converter was simulated and fabricated in 0.18 μm bipolar-complementary metal–oxide–semiconductor (MOS)-double-diffused MOS process. Experimental results show the features work well, and with 35 ns minimum on-time, this converter can convert up to 36 V input voltage to 1.8 V at 1 MHz switching frequency with single stage and compact solution. Measured peak efficiency is 89.5% and over 80% efficiency for 3 A output current is realised as well.

Protection of Autonomous Microgrids Using Agent-Based Distributed Communication

This paper presents a real-time implementation of autonomous microgrid protection using agent-based distributed communication. Protection of an autonomous microgrid requires special considerations compared to large-scale distribution networks due to the presence of power converters and relatively low inertia. In this paper, we introduce a practical overcurrent and a frequency-selectivity method to overcome conventional limitations. The proposed overcurrent scheme defines a selectivity mechanism considering the remedial action scheme of the microgrid after a fault instant based on feeder characteristics and the location of the intelligent electronic devices (IEDs). A synchrophasor-based online frequency-selectivity approach is proposed to avoid pulse loading effects in low inertia microgrids. Experimental results are presented for verification of the proposed schemes using a laboratory-based microgrid. The setup was composed of actual generation units and IEDs using the IEC 61850 protocol. The experimental results were in excellent agreement with the proposed protection scheme.

An Adaptive Overcurrent Protection Scheme for Distribution Networks

Distribution networks are evolving toward the vision of smart grids, with increasing penetration of distributed generation (DG), introduction of active network management (ANM), and potentially islanded modes of operation. These changes affect fault levels and fault current paths and have been demonstrated to compromise the correct operation of the overcurrent protection system. This paper presents an adaptive overcurrent protection system which automatically amends the protection settings of all overcurrent relays in response to the impact of DG, ANM, and islanding operation. The scheme has been developed using commercially available protection devices, employs IEC61850-based communications, and has been demonstrated and tested using a hardware-in-the-loop laboratory facility. A systematic comparison of the performance of the proposed adaptive scheme alongside that of a conventional overcurrent scheme is presented. This comparison quantifies the decrease in false operations and the reduction of mean operating time that the adaptive system offers.

An extended component-based reliability model for protective systems to determine routine test schedule

This paper presents a novel approach for evaluating the reliability of protective systems taking into account its components reliability. In this paper, a previously proposed extended model is used for a directional over-current scheme. In the extended model, the impacts of individual protective components are taken into account. An optimum routine test schedule is determined for each protective component as a separate unit. A comparison is made to show that the proposed approach has excellence over conventional routine test inspections. Impacts of factors such as circuit breaker inadvertent opening, required time for performing routine test inspections, human mistakes and self-checking and monitoring effectiveness is analyzed using the model. Redundancy in some parts of the protective system is examined. Permanent and transient faults on the protected zone, operation of backup protection and common-cause failures are also recognized in the model.