Modeling of TCC-based protective devices

This paper presents an artificial neural network (ANN) and support vector machine (SVM) approach for locating faults in radial distribution systems. Different from the traditional Fault Section Estimation methods, the proposed approach uses measurements available at the substation, circuit breaker and relay statuses. The data is analyzed using the principal component analysis (PCA) technique and the faults are classified according to the reactances of their path using a combination of support vector classifiers (SVCs) and feedforward neural networks (FFNNs). A practical 52 bus distribution system with loads is considered for studies, and the results presented show that the proposed approach of fault location gives accurate results in terms of the estimated fault location. Practical situations in distribution systems, such as protective devices placed only at the substation, all types of faults, and a wide range of varying short circuit levels, are considered for studies. The results demonstrate the feasibility of applying the proposed method in practical distribution system fault diagnosis.

Technological developments in protective devices have established the basis for appearance of numerical overcurrent relays (OCRs), which enable the users to apply their desired time‐current characteristics (TCCs). This study propounds novel stepwise and combined stepwise–piece‐wise linear TCCs and presents clear procedure to utilise them for coordinating OCRs in large meshed power systems. The TCCs keep constant time interval between the main/backup relay pairs within entire fault current range. They are examined first by coordinating the OCRs in a 4‐bus power system and by coordinating the ground fault OCRs in a practical 60 kV looped power system. Then, the OCRs of the IEEE 14‐bus test system, which is a rather large meshed power system with 39 OCRs and 102 main/backup pairs, are coordinated by using the novel TCCs. The same relays in the aforesaid power systems are coordinated using some non‐standard TCCs recently introduced in the literature. The comparison verifies that the lowest operating times are achieved by using the novel TCCs. The devised TCCs are simply formed as look‐up tables to be exactly set on the existing industrial relays. This fact is verified by setting them on an industrial OCR, and then, by testing the relay through the current injection method.

The rising demand for stable power supply in distribution systems has increased the importance of reliable supply. Thus, a networked distribution system (NDS) linked with individual lines is being adopted, gradually replacing the radial distribution system (RDS) currently applied to most distribution systems. Implementing the NDS can lead to various improvements in factors such as line utilization rate, acceptance rates of distributed power, and terminal voltages, while mitigating line losses. However, compared with the RDS, the NDS can experience bidirectional fault currents owing to its interconnected lines, thereby hindering protection coordination, which must be addressed before the NDS can be implemented in real-world power systems. Due to the characteristics of NDS, the reverse fault current is relatively small. However, this phenomenon becomes more severe when the high impedance fault (HIF) occurs. In this paper, the malfunction of protective devices during the HIF is directly verified and analyzed in the NDS. As a result, when the HIF occurs, the issue of the reverse protective device malfunctioning worsens because of a reduction in fault current and a failure in direction detection. To solve this issue, this work proposes a communication-based protection algorithm. Through the comparative verification of the proposed algorithm and the conventional protection method, protection coordination can be secured in the case of an HIF without new devices. It must be highlighted that the proposed method does not affect the settings of the protective device and provides a cost-effective and efficient solution since this algorithm is added independently to the existing relay.

The application of the residual current principle, as carried out by zero sequence current protective devices, is one of the most efficient ways to reduce the hazard of electric shock in case of the failure of equipment's basic insulation-to-ground. Highly sensitive, and regularly tested, residual current operated circuit-breakers without integral overcurrent protection devices (RCCBs) are rightfully recognized worldwide by standards and codes, as an effective means to protect persons against direct and indirect contact with energized parts by disconnecting the supply in a timely fashion. These devices are also referred to as ground fault circuit interrupters (GFCIs). The protective action of the RCCBs, though, can be nullified not only due to internal malfunctions of the device, but also due to particular ground-fault conditions. In these dangerous situations for persons, for example accidental direct contact with two parts at different potentials, the residual current flowing through the RCCB is below its residual operating value, and, therefore, it cannot trip. This hazardous circumstance exposes persons to dangerous touch voltages despite the presence of an efficient protective device, which cannot be blamed for not intervening. This paper seeks to clarify these particular fault conditions, occurring in the presence of healthy RCCBs.

The coordination between protective devices is the process of determining the most appropriate timing of power interruption during abnormal conditions in the power system. The aim of this work is to coordinate the protection of the 33/11 kV power distribution substation in Iraq using the CYME 7.1 software package. In this paper overcurrent and earth fault relays are simulated in two cases, with time delay setting and instantaneous setting, to obtain the Time Current Characteristics (TCC) curves for each Circuit Breaker (CB) relay of Al-Karama substation (2×31.5 MVA, 33/11 kV) in Babil distribution network. The short circuit current at each CB is calculated and accordingly, the protection coordination for Al-Karama substation has been simulated. The TCC curves have been obtained in two cases for overcurrent and earth fault relays; in a case with time delay setting and in the case with the instantaneous setting. The setting takes into consideration the short circuit current at the furthest point of the longest outgoing feeder and the shortest outgoing feeder.

Results of an undergraduate student project to perform a short-circuit and coordination study for a major industrial plant are presented in the form of a tutorial. The plant was supplied by parallel 34.4 kV lines from the utility which was reduced to 4.16 kV and distributed to five, dual-fed substations within the plant. Expansion of the plant required the addition of a sixth substation, which could affect the suitability of protective devices, and their settings, throughout the plant. The authors explain the procedure used to conduct the study, and discuss some considerations when developing the plant one-line diagram, calculating the available short-circuit currents, and coordinating the settings of series protective devices. >

Detection and experimental investigation of open conductor and single-phase earth return faults in distribution systems

The protective devices and switches play an important role in the reliability of electrical distribution systems by minimizing the impact of interruption. In this paper, a method for identifying the type and location for protection devices and switches on the prerouted distribution system using value-based optimization is proposed. The proposed method is based on the contingency analysis of various components, e.g., the faults of line sections, switches, protective devices, and the restoration through switching actions such as upstream restoration and downstream restoration. The formulation of the optimization problem in this paper is appropriate for linear integer programming, where each nonlinear term can be translated by only two additional linear constraints. The detailed design of the protection devices and the switches are determined by minimizing the total cost of reliability that comprises apparatus investment, maintenance, and interruption cost. The efficiency and validity of the proposed method are demonstrated in case studies.

The Differential Protection Scheme for Microgrid Using S-Transform

The added generating units in the electrical distribution network would affect the currents and voltages during fault conditions. Subsequently, these fault currents and voltages will influence the operation of relay protection units, circuit breakers, and safety measures at the inter-connection point with the utility. It is necessary to calculate those currents and voltages to select new protective devices or to re-tune the settings of the existing units. The chapter addresses fault conditions in electrical distribution networks that includes two types of distributed generators: induction generators—this subchapter addresses the short-circuit phenomenon and offers a modified way, as compared with the IEEE Standard, to assess the circuit breaker ratings; and single-phase synchronous generators—this subchapter summarizes the symmetrical component mathematical tool and offers a way of applying it when a three-phase system employs single-phase distributed generators.

The coordination of overcurrent relay protection in the power framework is crucial for preserving electrical distribution systems. It ensures that both primary and backup protection are provided to the system. It is essential to maintain a minimal level of coordination between these relays in order to reduce the overall running time and guarantee that power outages and damage are kept to a minimum under fault conditions. Proper coordination between the primary and back-up relays can minimize the operation duration of overcurrent with instantaneous and earth fault relays by selecting the optimum TMS (Time Multiplier Setting) and PS (Plug Setting). The present study investigates the difficulty associated with determining the TMS and PS values of earth-fault and overcurrent relays at the 33/11 kV power distribution substation in Basra using the instantaneous setting element. Overcurrent and earth fault relays were simulated in two scenarios: one with a time delay setting and one with an immediate setting. This procedure was carried out to generate Time Current Characteristics (TCC) curves for each Circuit Breaker (CB) relay took place in the Nathran substation, which has a capacity of 2×31.5 MVA and operates at a voltage level of 33/11 kV. The substation is a part of the Basrah distribution network. The short circuit current is estimated at each circuit breaker (CB), followed by the simulation of protection coordination for the Nathran substation using the DIgSILENT Power Factory software. This research is based on real data collection, and the setting considers the short-circuit current at the farthest point of the longest feeders. The results show the effectiveness of the proposed coordination scheme, which reduced trip operation time by 20% compared to the presented case study while maintaining coordination between primary and backup protection.

Successful identification of faults in a transmission line and quick isolation of the faulty section by operating appropriated protective devices is of significant importance for ensuring reliability and safety of power system. The present paper describes a method in which the three phase sending end voltage is used to obtain the Concordia pattern followed by feature extraction and classification of fault using probabilistic neural network. The present method is capable of accurately detecting the type of fault and also the location of the same in a given transmission line. Unlike other available techniques, evaluating Concordia pattern and extraction of features from it involve less computation. This in turn ensures fast operation of the proposed method. The performance of the proposed method is tested on the simulated data obtained from PSCAD model of a transmission line.

In the event of a fault isolation process, all loads located downstream from the faulted point become out of service, and as a consequence, the power interruption affects a greater portion of the radial distribution system. This paper proposes an optimal Service Restoration (SR) method that entails changing the network topology configuration via optimal tie-switch and section switch combinations. However, when the network topology configuration is performed, it results in increased load currents. As a result, some Protective Devices (PDs) can operate undesirably and some network branches may become unprotected. Therefore, it is essential to consider protection constraints in the SR problem to maintain service continuity during power interruptions. The proposed method aims at optimal SR with minimum out-of-service loads, minimum power loss, and improved voltage profiles and at the same time ensures PDs operate correctly during the normal and overloading conditions. The proposed method was carried out on the Debre Markos distribution networks, using the Teaching Learning Based Optimization (TLBO), Particle Swarm Optimization (PSO), and Differential Evolutionary (DEV) algorithms. The proposed SR was carried out considering and without considering protection constraints. The obtained SR topology was not feasible for SR without considering protection constraints, since some PDs fail to operate properly in normal loading conditions. After executing the proposed SR algorithms by considering protection constraints for a single fault case, the power loss reductions in TLBO, DEV, and PSO were 64.9073%, 45.9073%, and 55.358 %, respectively. The minimum voltage profiles obtained in each proposed TLBO, DEV, and PSO algorithm were 0.96%, 0.95%, and 0.96%, respectively. In each algorithm, except for the branch under fault, all healthy out-of-service branches were restored. When the protection constraints were considered in an optimal SR, load current did not exceed the rating of the fuses. The results show the importance of considering protection constraints during SR to prevent dysfunction of the PDs in the network. Comparative analyses were carried out on each algorithm and TLBO algorithms performed better than PSO and DEV for search functions.

This paper presents a decentralized fault detection technique for power distribution systems with resonant grounding. The aim of this paper is to detect single phase to ground faults and identify the faulty feeder within three cycles of the fault occurrence. In the proposed technique, faults are first detected based on the neutral voltage displacement. The pre-fault and post-fault voltages (phase to ground) are then used to identify the faulty phase. Finally, the faulty feeder (as well as the faulty area of a long feeder) is identified from the relationship between the initial transient of the zero-sequence current and the faulty phase voltage just after the occurrence of faults. A signal processing tool called mathematical morphology is utilized to identify the faulty feeder. To identify the faulty feeder, it is also required to know the fault occurrence time that is estimated using the slope of the neutral voltage. The main feature of the proposed scheme is that this technique only uses voltage and current signals from the corresponding voltage transformers and current transformers. Therefore, it does not require communication among protection devices in the same or different feeders to identify the faulty feeder. The proposed technique also has the ability to distinguish the nature of faults, i.e., whether the faults are permanent or temporary. The effectiveness of the proposed scheme is tested, on an IEEE test system as well as on a practical test system, using MATLAB/SimPowerSystems. Simulation results show that the proposed technique can quickly detect the single phase to ground faults in a resonant grounding power distribution system and identify the faulty feeder. It is also capable of distinguishing faults from other disturbances. Moreover, it works under different compensation levels as well as for different fault inception angles.

A recloser is a protection device used to mitigate long power interruptions during transient faults in passive distribution systems. Passive distribution systems are becoming active because of the integration of distributed generation. This generation introduces a reverse power flow and consequently a reverse fault current. The pick-up and operation time of the recloser can be affected because of the change in the fault current level. It is essential to study and compare the recloser's pick-up activity and operation time before setting the recloser in an active distribution system. This study, therefore, develops a virtual single-shot reclosing scheme and its performance tested in a passive and active distribution system. Matlab/SimulinkiSimscape power systems environment is used to simulate cases. Simulations are conducted for four case studies to identify issues in the performance of the recloser when there is distributed generation. The results show that the fault contribution of the distributed generation causes false tripping, protection blinding, and recloser-fuse misco-ordination.