Analysis of Protection Coordination for OCRs in DC Distribution System with Distributed Generation

<abstract> <p>More and more distributed energy resources (DERs) are being added to the medium-voltage (MV) or low-voltage (LV) radial distribution networks (RDNs). These distributed power sources will cause the redistribution of power flow and fault current, bringing new challenges to the coordination of power system protection. An adaptive protection coordination strategy is proposed in this paper. It will trace the connectivity of the system structure to determine the set of relay numbers as a tracking path. According to the topology of the system structure, the tracking path can be divided into two categories: the main feeder path and the branch path. The time multiplier setting (TMS) of each relay can be used to evaluate the operation time of the over-current relay (OCR), and the operation time of the relay can be used to evaluate the fitness of the TMS setting combination. Furthermore, the relay protection coordination problem can be modeled to minimize the accumulated summation of all primary and backup relay operation time (OT) subject to the coordination time interval (CTI) limitation. A modified particle swarm optimization (MPSO) algorithm with adaptive self-cognition and society operation scheme (ASSOS) was proposed and utilized to determine TMS for each relay on the tracking path. A 16-bus test MV system with distributed generators (DGs) will be applied to test the adaptive protection coordination approach proposed in this paper. The results show that the proposed MPSO algorithm reduces the overall OT and relieves the impact on protection coordination settings after DG joins the system. The paper also tests and compares the proposed MPSO with other metaheuristic intelligence-based random search algorithms to prove that MPSO possesses with increased efficiency and performance.</p> </abstract>

DC fault current is contributed by various distributed energy resources in DC distribution systems. Most DC distribution systems have low line impedance. The fault current increases fast because of the low impedance. Some converters in DC distribution systems include Fault Current Limiting (FCL) function. The controlled fault currents at different locations are very close. Thus, it is important to design a reliable and fast fault detection and location method for DC distribution systems. This paper proposes a novel local measurement-based fault location algorithm for DC distribution systems. The proposed fault location algorithm can estimate the equivalent inductance from a protective device to a fault in less than one millisecond. The performance of the developed protection algorithm was validated in both numerical simulation and hardware testing.

In this study, optimal distribution network protection coordination scheme with directional over current relays is developed. In addition, impact of optimally placed Distribution Generation (DG) on the protection coordination scheme is subsequently evaluated using relay Coordination Time Interval (CTI). As such, the study is carried out in two stages. In the first stage, optimal relays settings (time dial settings and pickup current) are determined. While in the second stage, the maximum DG penetration level with changes in the protection coordination is evaluated. Particle Swarm Optimization (PSO) algorithm, due to its faster convergence speed, is applied in both stages. The technique is implemented on the distribution section of the IEEE 14-bus and IEEE 30-bus systems and simulated in MATLAB. The simulation results obtained are compared with that obtained using hybrid Genetic Algorithm (GS) – Nonlinear Programming (NP) approach using relays pickup current and operating times as performance metrics. For the IEEE 14 bus system, the developed PSO-based relay coordination has reduced the relays pickup current and operating times by roughly 28% and 32% respectively compared with the hybrid GA-NLP technique. The optimal locations of the DGs are found to be bus 5, 8 and 12 which result in CTI of 0.233sec. While in the IEEE 30 bus system, the developed relay coordination has reduced the relays pickup current and operating times by roughly 31% and 34% respectively compared with the hybrid GA-NLP technique. Similarly, the optimal locations and sizes of the DGs are found to be bus 19, 26 and 30, which result in CTI of 0.462sec.

Effect of non standard characteristics of overcurrent relay on protection coordination and maximizing overcurrent protection level in distribution network

Due to the concerns for reduction of system losses, providing back-up power during loss of the grid, mitigation of energy security risks and conspicuous perturbation of power outages triggered by severe environmental constraints; the modernized distribution grids elicited grid resiliency and reliability enhancement through pragmatic enforcement of the Microgrid (MG) concept with distributed generation. With the proliferating power ultimatum, several intricate factors prone to MG operation modes, bidirectional power flow complexities, management and control of power transfer, varying fault current contribution, and high impedance faults (HIF) customized the network configuration and imperiled the protection system operation and system stability. The propitious utility framework persuaded the prerequisites to embrace the integration of state-of-the-art affiliated Distributed Energy Resources (DERs), which requires assimilated and coordinated studies to emphasize the outcomes of an efficient, reliable, and fast protection scheme for both the grid-connected and islanded modes of operation. Operating modes of distributed generation (DG) will affect the magnitude and direction of fault currents resulting in failure of protection coordination between directional overcurrent relays (DOCRs). In this paper, the negative-sequence based adaptive directional overcurrent relay (NSADOCR) stratagem is proposed. Protection coordination is accomplished by a new adaptive approach, which alters time dial setting (TDS) of negative-sequence overcurrent relay based on the ratio of the normal mode to operating mode of plug setting multiplier function. Furthermore, the direction of fault is attained using phase change in between the pre-fault and superimposed negative-sequence current components. Performance of the NSADOCR is evaluated on the dSPACE controller board, which is interfaced with Real- Time Digital Simulator (RTDSTM) to perform the hardware-in-the-loop (HIL) tests. Extensive simulation studies and hardware results on DG systems exemplify and indicate that the new adaptive technique results in effective protection coordination over the conventional approach, considering various distribution network (DN) modes of operation.

High penetration level of distributed generation (DG) leads to improper protection coordination of the distribution system. In this paper, multiple DG locations are considered to evaluate the protection coordination index value. Due to the penetration of DG causes the change in fault current levels. So to prevent relay maloperation, change in co-ordination of relays is required. Further fault current limiters are used to enhance protection coordination index. Fault currents reduced within the breaking capacity of protective devices when FCL is introduced into the system in the presence of DG penetration. IEEE-14 bus test system is considered in the analysis. A mixed integer PSO Algorithm is used to enhance PCI index and to find optimal FCL size.

Distributed Generation (DG) has emerged as best alternative to conventional energy sources in recent times. Decentralization of power generation, improvement in voltage profile and reduction of system losses are some of key benefits of DG integration into the grid. However, introduction of DG changes the radial nature of a distribution network (DN) and may affect both magnitude and direction of fault currents. This phenomenon may have severe repercussions for the reliability and safety of a DN including protection coordination failure. This paper investigates the impact of DG on protection coordination of a typical DN and proposes a scheme to restore the protection coordination in presence of DG. Moreover, impact of different DG sizes and locations on DN’s voltage profile and losses has also been analyzed. The sample DN with embedded DG is modelled in ETAP environment and the simulation results presented show the effectiveness of the proposed protection strategy in restoring relay coordination of the network in both isolated and DG connected modes of operation.

DC distribution system has advantages of high power quality, large transmission capacity, high reliability, simple structure, economy and low energy consumption, and so forth. It has been a key part of smart grid nowadays. However, the development of DC distribution system is constrained by the lack of operational experience in DC system, the small interrupting capacity of DC circuit breaker (CB), and the lack of protection schemes for system itself. In this paper, protection for DC distribution system with distributed generator (DG) is fully investigated and verified. Firstly, the electromagnetic transient model of DC distribution system with DG is presented. Simulation based on the electromagnetic transient model is carried out. Both the step response and the steady-state performance verify the accuracy of the model. Then the fault characteristic mechanism is analyzed, and the protection principles and scheme are investigated in detail, including voltage mutation principle as protection starting component, differential current protection principle for DC bus, and two-section current protection for distribution lines. Finally, transient responses with protection scheme are analyzed during faults. The results present that the protection principles and scheme are feasible for DC distribution system with DG.

The potential benefits of direct current (DC) network in low‐voltage system promote smart grids and facilitate increasing penetration of distributed generation (DG). Correct identification of faulted section of a distribution network by an automation system reduces power outage time and improves reliability indices of such systems. With the onset of a fault in a DC distribution system, data recorded at an outage management system are used to identify the faulted section. With DG units active in a distribution system, there will be bidirectional power flow and faulted section identification becomes challenging. Using voltage and current data from consumer‐end smart meters and the substation, a method is proposed to identify the faulted section in DC distribution system. The Hadamard product of fault‐affected sections (obtained from network topology and voltage status matrices) is used to identify the faulted section correctly. Using power systems computer‐aided design/electro‐magnetic transient design and control simulation, the accuracy of the proposed method is verified for different fault situations including simultaneous faults, fault close to a bus and with rooftop photovoltaic integration to a DC distribution system. The method has the capability to provide information on the fault segment that connects feeder pillar to the consumer end also.

SUMMARYThis paper studies a DC distribution system, which has been supplied by utility AC grid and converter‐based distributed generation (DG) in order to provide an overall solution to power quality problems. The power flow control in DC distribution systems is achieved by network and storage converters, which have DC voltage controllers. A control strategy for these converters has been presented, which is based on DC voltage droop controller and a novel instantaneous power regulation scheme. Furthermore, this paper presents a simple DC bus voltage controller, which can be used for DC system voltage determination. Also, a novel control system has been proposed for DG and load converters. The simulation results, based on PSCAD/EMTDC software, show that DC distribution system including converter‐based DG unit can provide the premium power quality. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents a novel fault current management (FCM) technique for radial distribution systems with embedded inverter-based distributed generators (IB-DGs). At the point of connection to a power system, many distributed generators (DGs) require power electronic (PE) interfaces, which are normally idle during faults. The proposed FCM method employs these PE interfaces for control of the fault current. For this purpose, operation of IB-DGs is modified to FCM mode at the moment of fault and new current references are applied. Of the two controllable parameters of the IB-DG output current-current magnitude and current phase angle-the current phase angle is chosen as the means of controlling the fault current magnitude. The reference current phase angle is calculated based on the relation between the fault current elements and their phase angles. As a result of this novel operation, IB-DGs with larger capacity can be connected at different locations of the system without affecting the fault current magnitude. Also, implementing this technique in smart grids is economically proven, since the asset of power system which have been designed for normal operation are employed to manage the fault current magnitude. Moreover, possibilities of synchronization problems are reduced by keeping IB-DGs connected to the system at all the time. The evaluation of the proposed FCM technique using the standard IEEE 33-bus distribution system demonstrates the effectiveness of the proposed method for managing the fault current magnitude.

As one of the countermeasures to solve the increase problem of the fault current in a power system, the superconducting fault current limiter (SFCL) has been noticed as the attractive device because it has no power loss in a normal time and can limit the fault current rapidly without additional device to detect the fault current. However, the introduction of the SFCL in a power distribution system affects the protection coordination between the existing protective devices such as the over-current relay (OCR) and the recloser, which causes the operation of the protective devices to get out of their original setting values. Therefore, the analysis on the effect of the SFCL introduction on the existing protective devices is required and the method to keep the protection coordination between the protective devices in a power system with the SFCL should be first considered. In this paper, the protection coordination experiments between the OCR and the recloser in the simulated power distribution system with the SFCL were performed. Based on the experimental results, the influence of the SFCL on the operation of these protective devices was analysed and the methods to keep the protection coordination between the OCR and the recloser in a power distribution system with the SFCL were discussed.

Distributed generation (DG) is commonly used to supply the local loads. The penetration of distributed generation leads to violating the relay coordination in the distribution network. The interconnection of DG affects miscoordination of distribution system protection, because of the generator ability to contribute large fault currents to the fault point. The impact of DG on relay coordination affect the operating time of relay. The CTI associated with primary and backup relay pairs is getting violated due to changes in fault current level. Thus, coordination between primary and backup relays fails in the presence of distributed Generation. Hence, the interconnection of DG in the distribution system causes an adverse impact on protection coordination. Relay coordination problem has many constraints due to coordination criteria. Heuristic based optimization techniques are used to solve the optimization problems. These techniques have a drawback of converging to the values that may not be optimum due to the wide range of design variables and difficulty in getting an initial feasible solution with a short range of design variables. This paper presents a new algorithm to overcome the problem of the initial feasible solution in determining the optimum settings of OCRs. In this context, the optimization problem is formulated as constrained non-linear optimization problem and is determining using Genetic Algorithm (GA). This algorithm is tested on two different networks that found suitable to give satisfactory results.

In recent years, distributed generation (DG) has become more common in modern distribution networks (DNs). The presence of these small-scale generation units within a DN brings new challenges to protection engineers, since short-circuit currents tend to increase; additionally, as with microgrids, modern DNs may feature several operational modes depending on their topology and the availability of DG. This paper presents a methodology for the optimal coordination of overcurrent relays (OCRs) in modern DNs with a high presence of DG. Given the fact that protection coordination is a non-linear and non-convex optimization problem, a hybrid harmony search and simulated annealing (HS-SA) approach was implemented for its solution and compared against other techniques, such as conventional HS, genetic algorithm (GA), particle swarm optimization (PSO) and hybrid PSO-HS. Several tests were performed on a DN, considering different operative scenarios as a function of the DG available within the network. A comparison with other works reported in the specialized literature was carried out, evidencing the applicability and effectiveness of the HS-SA technique in solving the optimal OCR coordination problem in modern DNs.

Comprehensive coordination of radial distribution network protection in the presence of synchronous distributed generation using fault current limiter