Overcurrent Settings Research Articles

Protection of the Future Harbor Area AC Microgrids Containing Renewable Energy Sources and Batteries

A significant share of global carbon emissions is related to marine vessels running solely on fossil fuels. The hybrid or fully electrified marine vessels using battery energy storage systems (BESS) both for onboard propulsion system and for cold-ironing during docking at harbor areas will significantly reduce marine related carbon emissions. However, the transformation of marine vessels’ operations from diesel engines to BESS will necessarily require charging stations and other electric power infrastructure at harbor areas. The sustainable and cheap energy of renewable energy sources like wind turbine generators (WTGs), photovoltaic (PV) systems and related BESS could be used at harbor areas for charging depleted vessel-BESS and supplying power to cold-ironing loads. For this purpose, two new harbor area smart grid or AC microgrid models have been developed by our research group. This paper presents a comprehensive analysis of three-phase short-circuit faults for one of the proposed AC microgrid models using PSCAD/EMTDC simulations. The fault study of harbor area AC microgrid-1 is done for both grid-connected and islanded modes. The main purpose of the fault study is to check if grid-connected mode overcurrent settings of intelligent electronic devices (IEDs) will also be valid for different islanded mode fault cases with different fault current contributions from converter-based distributed energy resources (DERs) including WTG, PV and BESS. The extent of fault current contribution from DERs and BESS to avoid adaptive protection settings and to ensure definite-time protection coordination and fast fuse operations during different islanded modes is investigated.

Optimal Coordination of Time Delay Overcurrent Relays for Power Systems with Integrated Renewable Energy Sources

With the gradual increase in load demand due to population and economic growth, integrating renewable energy sources (RES) into the grid represents a solution for meeting load demand. However, integrating RES might change the power system type from radial to non-radial, where the current can flow forward and backward. Consequently, power system analysis methods must be updated. The impact on power systems includes changes in the load flow affecting the voltage level, equipment sizing, operating modes, and power system protection. Conventional power system protection methods must be updated, as RES integration will change the power flow results and the short circuit levels in the power system. With an RES contribution to short circuit, existing settings might experience missed coordination which will result in unnecessary tripping. This paper considers the impact of integrating renewable energy sources into power system protection on overcurrent time delay settings. A new method to upgrade/adjust time delay settings is developed utilizing genetic algorithm (GA) optimization. The proposed optimization method can be used to evaluate the impact of integrating RES on the exiting overcurrent setting, and can provide new settings without the need to replace existing protection devices when the short circuit is within equipment thermal limits.

Development of a fast large-current electronic breaker using the dual-path switching method

ABSTRACT Currently, a circuit breaker or fuse is widely used as a fast electrical switch to protect electronic equipment from overload or short circuit. However, the fuse usually requires more than 0.05 s to react, and the breaker takes even much longer time. To overcome this limitation, a fast high-current AC electronic breaker using a dual-path switching method is proposed. First, the surge current is forced to go through a soft-start circuit controlled by a TRAIC. Then, the load current is switched to the dual silicon-controlled rectifier (SCR) circuit for overload protection control. The current is measured using a current transformer and then converted to a voltage signal for amplification. A slave microprocessor is in charge of receiving the amplified signal and controlling both soft-start and dual SCR circuits. A master microprocessor is mainly used to send/receive overcurrent setting and control signals to/from the slave microprocessor. The temperature of the dual SCR with a radiator fan can be suppressed well to a value much lower than the maximum rating one. The experimental results verify that the proposed method can effectively limit the surge current and achieve a large overcurrent protection up to 40 A within 10 ms.

Dynamic Adaptive Protection based on IEC 61850

In electrical power systems, the overcurrent relays (ANSI/IEEE 50/51) are widely used for protection, and it is one of the main alternatives for identifying system faults. In radial systems supplied by a single source, protection and selectivity can be achieved using the traditional techniques based on time-current curves coordination. However, in a system with multiple sources and operational conditions, traditional techniques are not sufficient to obtain selectivity. This paper presents an adaptative protection system which, based on IEC 61850, adjusts the protection to changes in the power system. The proposal uses a communication network to change the overcurrent settings according to the sources in operation. The performance of the proposed system was evaluated in a case study. The system is composed of five independent power supplies, a utility and four cogeneration units with different rated power; thus 15 combinations of sources are possible during islanding conditions. The results demonstrate that the proposal can provide the selectivity of the system in any operational condition.

Overcurrent protection scheme for collector lines in wind farm based on fault component current correlation analysis and multi‐agent system

Collector line relay failures of large-scale grid-connected wind farms have not received much attention so far. In this study, the adaptability of conventional overcurrent setting method is analysed when used in doubly fed induction generator-based wind farms, revealing the coordination difficulties between collector line relay and fuse protection of wind turbine (WT) branch as well as the potential maloperation causes of backup overcurrent relays (BOCRs). Then, a novel three-stage setting method of overcurrent relays is proposed. In view of time-bound instantaneous overcurrent relays, a time delay setting approach is put forward considering the time–current characteristic of fuses. Based on the multi-agent system, which is both flexible and effective, comprehensive criteria containing fault component current correlation analysis and differential current criterion are applied to BOCRs. The proposed scheme is validated by the simulation of 46-WT wind farm on DIgSILENT/Powerfactory platform. Simulation results show that the relay is able to trip within 0.32 s and the BOCRs perform well when confronting single fault or even multiple faults.

Method for identification of grid operating conditions for adaptive overcurrent protection during intentional islanding operation

Currently, it is considered that distributed synchronous generators may operate in intentional-islanding operation mode, in which a portion of the power grid, which consists of load and distributed generation, is isolated from the remainder of the utility system. However, the fault current level of the feeders drastically decreases when the utility grid is disconnected and the protection will not properly operate if the overcurrent settings are not changed. In this paper it is proposed a method for identification of the grid operating conditions, utility connected or islanded. The method is based on the use of a local scheme installed close to the protection device. The scheme uses a thyristor which is fired during a short waveform interval of voltage. The thyristor voltage and current are monitored and used to calculate the grid equivalent impedance. According to the grid equivalent impedance it is possible to determine whether the utility is connected or not. Simulations considering a distribution system and a distributed synchronous generator are used to validate the proposed method. The results show that the method can be used to update the protection settings when the operating condition of the system is changed from utility-connected to islanded operation mode or vice-versa. As a result, the method allows implementing an adaptive protection without the use of communication system or can be used as a backup to increase the resilience in case the communication is lost.

Comparison of Programmable Logic and Setting Group Methods for adaptive overcurrent protection in microgrids

Adaptive overcurrent protection systems for microgrids with distributed generators require that overcurrent relays need to be adjusted to different circuit paths and feeder fuses. Adaptive overcurrent protection systems in recent publications were based on the Setting Group method, using the functions resident in the relay. In this paper, the Programmable Logic method was developed for an adaptive overcurrent protection system, using the programmable logic and math operators instead of the functions resident in the relay. The Programmable Logic and Setting Group methods were validated using a real-time simulator with two relays in-the-loop. The selectivity, reliability and speed of the adaptive protection system based on the Programmable Logic and Setting Group (previous work) methods were compared for a microgrid with distributed generators (diesel generators). Similar results were obtained with both methods. However, the Setting Group method limited the number of overcurrent settings by the available setting groups of relays, and disabled the relays for a fixed amount of time, reducing the relay’s availability. On the other side, the Programmable Logic method is recommended because it improves the capacity of relays by using one setting group, and avoids relays to be disabled because switching setting groups is not being necessary. In microgrids that require an adaptive overcurrent protection system for different circuit paths and seasonal (winter and summer) settings, adaptive overcurrent protections based on programming alternative is a better solution. This requires relay engineers to be trained in relays’ programming techniques.

Fuse relay adaptive overcurrent protection scheme for microgrid with distributed generators

Utilities have installed distributed generators to improve reliability of the power distribution system. Distributed generators at various sites provide additional circuit paths in case energy provision to the end user is interrupted by a blackout or equipment failure. When the microgrid is working on island and grid-connected modes, overcurrent protections in power lines must be adjusted to different distributed generator circuit paths and feeder fuses in the microgrid. This study presents an adaptive overcurrent protection that integrates technical and economic advantages of fuses and relays in a microgrid with distributed generators. This fuse relay adaptive overcurrent protection (FRAOP) scheme protects power lines and feeders by grouping identical inverse time overcurrent settings of relays, and logic gates of relay's breakers. Selectivity, reliability, and speed of the FRAOP was verified by a real-time simulator with relays in-the-loop.

Adaptive feeder load management and control during distribution power restoration based on DA and AMI systems integration approach

Abstract In order to ensure reliability and availability of power during emergency conditions like faults, power restoration schemes are incorporated in Distribution Automation (DA) systems. DA system restores power to loads that are not affected by fault through short-term feeder reconfiguration. During this reconfiguration process of switching additional loads to healthy feeders for power restoration purpose, it is critical to manage and control the feeder overall load and to compute and update over-current settings of breakers in corresponding feeder relays adaptively and accurately. This would avoid possible mal-operation of feeder relays due to overload violations, if any after restoration. In this paper for the first time in literature, we introduce a unique algorithm for accurate over current setting computation of feeder relays based on proposed load segmentation approach used for DA and Advanced Metering Infrastructure (AMI) systems integration. This method further helps DA in managing the feeder load adaptively during and after restoration based on AMI system capabilities, including smart meters priority based load curtailment and distributed generation management. A case study on standard RBTS 33kV distribution system is demonstrated.