Standard Characteristic Curve Research Articles

Microgrid Protection Coordination Considering Clustering and Metaheuristic Optimization

This paper addresses the protection coordination problem of microgrids combining unsupervised learning techniques, metaheuristic optimization and non-standard characteristics of directional over-current relays (DOCRs). Microgrids may operate under different topologies or operative scenarios. In this case, clustering techniques such as K-means, balanced iterative reducing and clustering using hierarchies (BIRCH), Gaussian mixture, and hierarchical clustering were implemented to classify the operational scenarios of the microgrid. Such scenarios were previously defined according to the type of generation in operation and the topology of the network. Then, four metaheuristic techniques, namely, Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Invasive Weed Optimization (IWO), and Artificial Bee Colony (ABC) were used to solve the coordination problem of every cluster of operative scenarios. Furthermore, non-standard characteristics of DOCRs were also used. The number of clusters was limited to the maximum number of setting setting groups within commercial DOCRs. In the optimization model, each relay is evaluated based on three optimization variables, namely: time multiplier setting (TMS), the upper limit of the plug setting multiplier (PSM), and the standard characteristic curve (SCC). The effectiveness of the proposed approach is demonstrated through various tests conducted on a benchmark test microgrid.

Protection Coordination of Microgrids Considering Non-Standard Features of Directional Over-Current Relays

This paper presents a methodology for protection coordination in microgrids that considers account non-standard features of directional over-current relays (OCRs). In the proposed approach three decision variables are considered for each relay; namely, the standard characteristic curve (SCC), Time Multiplier Setting (TMS) and maximum limit of the plug setting multiplier (PSM). The proposed mixed integer non-linear programing model is solved by means of a specialized genetic algorithm (GA) implemented in Matlab. Several tests were performed on a modified version of the IEEE-30 bus test system considering on-grid and off-grid operational modes. The results evidenced the robustness and applicability of the proposed approach in real-size microgrids that host distributed generation and exhibit several operational modes or topologies.

Adaptive protection coordination scheme in microgrids using directional over-current relays with non-standard characteristics

Protection coordination of AC microgrids (MGs) is a challenging task since they can operate either in grid-connected or islanded mode which drastically modifies the fault currents. In this context, traditional approaches to protection coordination, that only consider the time multiplier setting (TMS) as a decision variable may no longer be able to guarantee network security. This paper presents a novel approach for protection coordination in AC MGs that incorporates non-standard characteristic features of directional over-current relays (OCRs). Three optimization variables are considered for each relay: TMS, maximum limit of the plug setting multiplier (PSM) and standard characteristic curve (SCC). The proposed model corresponds to a mixed integer non-linear programming problem. Four metaheuristic techniques were implemented for solving the optimal coordination problem, namely: particle swarm optimization (PSO), genetic algorithm (GA), teaching-learning based optimization (TLBO) algorithm and shuffled frog leaping algorithm (SFLA). Numerous tests were run on an IEC MG as well as with the distribution portion of the IEEE 30-bus test system. Both systems incorporate distributed generation (DG) and feature several modes of operation. A comparison was made with other MG protection coordination approaches proposed in the specialized literature. In all cases, the proposed approach found reduced coordination times, evidencing the applicability and efficacy of the proposed approach.

Linear Decision Rules for Control of Reactive Power by Distributed Photovoltaic Generators

The revised IEEE 1547 Standard together with the grid codes from several European countries require the contribution of photovoltaic inverters to the reactive power and voltage control of distribution networks. This paper presents a decentralized approach for controlling reactive power from a photovoltaic (PV) inverter through a linear decision rule that is in terms of the PV generated real power, conforming to standard characteristic curves in the German grid code. The linear decision rules are computed using an affinely adjustable robust counterpart of an optimal power flow type formulation, with the PV real power generation specified in an uncertainty interval. The robust solution, which is computed via convex quadratic programming, guarantees that both the voltage deviations and power loss will remain within their optimized bounds for all realizations of PV real power sampled from the uncertainty set. The proposed linear decision rules are compared with a local control method that seeks the same type of multiobjective optimization. Monte Carlo simulation results on meshed distribution networks with up to 830 nodes show the superiority of the proposed approach.

A nano measurement machine equipped with a 3D piezo-resistive micro tactile probe

A 3D micro tactile probe based on piezo-resistive effect is developed for dimensional metrology and a detailed analysis on the hysteresis, resolution, crosstalk and uncertainty of the probe is presented. A Nano Measurement Machine (NMM) equipped with the 3D micro tactile probe is proposed as a new high precision zero-point indicator for micro- and nano-scale traceable dimensional measurement, which is calibrated according to the standard characteristic curve. In 1mm step-height standard measurement experiment using the 3D piezo-resistive micro tactile probe, the experimental results show a standard deviation of 37nm in the vertical tactile direction and one of 104nm in transverse tactile direction while the standard deviation is 40nm in the vertical direction in the 2mm step-height standard measuring experiment.

Coordinated Active Power-Dependent Voltage Regulation in Distribution Grids With PV Systems

High penetrations of photovoltaic (PV) systems in distribution grids have brought about new challenges such as reverse power flow and voltage rise. One of the proposed remedies for voltage rise is reactive power contribution by PV systems. Recent German Grid Codes (GGC) introduce an active power dependent (APD) standard characteristic curve, ${\rm Q}({\rm P})$ , for inverter-coupled distributed generators. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to locally and systematically develop a coordinated ${\rm Q}({\rm P})$ characteristic for each PV system along a feeder. The main aim of this paper is to evaluate the technical performance of different aspects of proposed ${\rm Q}({\rm P})$ characteristics. In fact, the proposed method is a systematic approach to set parameters in the GGC ${\rm Q}({\rm P})$ characteristic. In the proposed APD method the reactive power is determined based on the local feed-in active power of each PV system. However, the local voltage is also indirectly taken into account. Therefore, this method regulates the voltage in order to keep it under the upper steady-state voltage limit. Moreover, several variants of the proposed method are considered and implemented in a simple grid and a complex utility grid. The results demonstrate the voltage-regulation advantages of the proposed method in contrast to the GGC standard characteristic.

Detecting and solving the coordination curve intersection problem of overcurrent relays in subtransmission systems with a new method

This study presents a practical and effective method for inspecting and repairing curve intersection situations that occur in upstream and downstream coordinated overcurrent relay pairs in subtransmission networks. This type of miscoordination can cause backup relays to trip before their paired primary when faults occur, resulting in unexpected expansions of blackout areas. The proposed method is based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays and a customized curve equation for electromechanical overcurrent relays. Consequently, the proposed method is applicable to both digital and electromechanical relays. Two subtransmission network cases for the Taiwan Power Company were simulated to validate the proposed method.

Study of Solving the Coordination Curve Intersection of Inverse-Time Overcurrent Relays in Subtransmission Systems

This paper presents a practical and effective novel approach to solve the coordination problem caused by the curve intersection of overcurrent relays in subtransmission systems. Based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays, as well as the simulation curve equation for electromagnetic overcurrent relays, lever setting adjustment equations for a selected point on the characteristic curve is derived. Then, centered on the derived equations, a dedicated software program is developed to compute the corresponding relay lever setting with different tap value in order that, passing through the selected point, another curve with the new lever setting is chosen. Finally, assisting with the graphical capability of the commercial ASPEN OneLiner, the proposed fixed-point coordination curve adjustment procedure can completely eliminate the coordination curve intersections. In addition, an actual case of a subtransmission network in Taiwan Power Company is simulated to validate the feasibility of the technique proposed.

A Novel Approach to Fast Eliminating the Characteristic Curves Crossing Problem of Relay Coordination in Radial Subtransmission Networks

A novel approach is presented to solve the coordination problem of overcurrent relays in radial subtransmission networks resulting from the intersection of characteristic curves. Based on the ANSI/IEEE standard characteristic curve equation of digital overcurrent relays, a slope adjustment equation for a selected point on the characteristic curve is derived and then used as the core of a dedicated software program developed to compute the corresponding relay setting with different tap value in order that, passed through the selected point, another curve with steeper slope is chosen and thus able to escape from the crossed position. Finally, with the assistance of the graphical capability of commercial package OneLiner in drawing the upstream and downstream relay coordination curves after adjustment, the curves intersection problem in protection coordination can be readily eliminated. In addition, an actual case of a radial subtransmission network with six buses in Taiwan Power Company is simulated to validate the feasibility of the approach.

SU‐FF‐T‐426: The Response of RadioChromic EBT Film in High‐Energy Electron Beams

Purpose: To describe the response of a new radiochromic film to highenergy clinical electron beams. GAFChromic® EBT film was designed primarily for verification of high energy photon IMRT treatments. It has been shown to be a very accurate and convenient photon detector. However, there is no literature on this film's response to high‐energy electron beams. We initiated a study to characterize the response and utility of this film for routine electron beam dosimetry. Method and Materials: The linac was first calibrated to ensure that the delivered dose was known accurately. We exposed a series of EBT films at dmax in polystyrene to 6, 9, 12, 16, and 20 MeV electrons to develop standard characteristic curves. All films were from the same batch. We also exposed the EBT films in a solid water phantom to produce central axis depth dose curves. These data were compared against percent depth dose curves measured with either Kodak XV2 film in a solid water cassette, or in a water phantom using an IC‐10 ion chamber or a PTW electron diode. Results: Results showed that the characteristic curve for this film was the same for electron energies from 6–20 MeV. Also, the response of the EBT film along the central axis of the beam matched the central axis percentage depth dose characteristics (R50, Rp) determined using Kodak XV2 film, electron diodes, and corrected ionization chamber measurements. Conclusion: GAFChromic® EBT film is shown to be an accurate detector for clinical electron beam applications. It is convenient to use since the solid water film cassette can be loaded in the linac room and requires no post‐irradiation processing. It gives the same results for electron dosimetry as silver halide films, diodes, and ionization chambers. Research sponsored by International Specialty Products corporation.

The response of Kodak EDR2 film in high-energy electron beams.

Kodak XV2 film has been a key dosimeter in radiation therapy for many years. The advantages of the recently introduced Kodak EDR2 film for photon beam dosimetry have been the focus of several IMRT verification dosimetry publications. However, no description of this film's response to electron beams exists in the literature. We initiated a study to characterize the response and utility of this film for electron beam dosimetry. We exposed a series of EDR2 films to 6, 9, 12, 16, and 20 MeV electrons in addition to 6 and 18 MV x rays to develop standard characteristic curves. The linac was first calibrated to ensure that the delivered dose was known accurately. All irradiations were done at dmax in polystyrene for both photons and electrons, all films were from the same batch, and were developed at the same time. We also exposed the EDR2 films in a solid water phantom to produce central axis depth dose curves. These data were compared against percent depth dose curves measured in a water phantom using an IC-10 ion chamber, Kodak XV2 film, and a PTW electron diode. The response of this film was the same for both 6 and 18 MV x rays, but showed an apparent energy-dependent enhancement for electron beams. The response of the film also increased with increasing electron energy. This caused the percent depth dose curves using film to be shifted toward the surface compared to the ion chamber data.

95/01532 Distributed approach to black point

This study presents a practical and effective method for inspecting and repairing curve intersection situations that occur in upstream and downstream coordinated overcurrent relay pairs in subtransmission networks. This type of miscoordination can cause backup relays to trip before their paired primary when faults occur, resulting in unexpected expansions of blackout areas. The proposed method is based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays and a customized curve equation for electromechanical overcurrent relays. Consequently, the proposed method is applicable to both digital and electromechanical relays. Two subtransmission network cases for the Taiwan Power Company were simulated to validate the proposed method.