Investigation of TCSC and SSSC Controller Effects on the Power System

Abstract Electrical power systems have been growing due to the increased demand and various loads and it is getting more and more difficult to provide stability and control. It is possible to increase line transmission capacities and to control these systems by providing reactive power compensation. In the recent years, FACTS (Flexible Alternative Current Transmission System) devices have been used as reactive power compensation elements. The study utilized rapid responding TCSC (Thyristor Controlled Series Capacitor) and SSSC (Static Synchronous Series Compensator) FACTS devices that are formed by power electronics elements. The effects of these devices on voltage stability, on the powers carried on the lines and the losses that occur on the lines were investigated with the simulation and its results

Crowbar hardware design enhancement for fault ride through capability in doubly fed induction generator-based wind turbines

A crowbar circuit used in doubly fed induction generator (DFIG)-based wind turbines protects the system during transient stability. However, in a large power system, crowbar protection may be insufficient due to over-voltage and inrush currents occurring during balanced and unbalanced faults. Hence, in this study, a crowbar circuit was enhanced for fault ride through capability against balanced and unbalanced faults in a DFIG. The stator and rotor dynamic modeling used a crowbar hardware circuit design with rotor active impedance. Electromotive force voltages were used for the stator-rotor dynamics in the DFIG. Furthermore, crowbar resistance units were designed to meet the fault ride through DFIG requirement. The DFIG behaviors with and without the crowbar hardware circuit design were compared. The balanced and unbalanced faults were also compared in terms of behavior. Results showed that the circuit design of the crowbar hardware enabled the system to promptly become stable and eliminated the oscillations. (C) 2020 ISA. Published by Elsevier Ltd. All rights reserved.WOS:0005714625000012-s2.0-85085073130PubMed: 3242361

Hybrid control approach for low-voltage ride-through capability in doubly-fed induction generator-based wind turbines

Grid-connected doubly-fed induction generator (DFIG)-based wind turbines are very sensitive to voltage dip problems that occur in grid side. Therefore, different low-voltage ride-through (LVRT) capability methods are used to decrease the voltage dip problems. In this study, it is aimed to present a hybrid control approach to provide LVRT capability in DFIG. Moreover, it is aimed to develop electromotive-force (emf) models in a stator-rotor circuit. The rotor emf model is used to compensate for the voltage dip and reduce the oscillations while using the stator emf model to ensure the ease of calculation and accuracy of the simulation study. In the results, this paper is reporting that the hybrid control approach proposed in this study has given yield effective and better results in comparison with those of the conventional DFIG model.WOS:0006443282000062-s2.0-8510004235

Novel active-passive compensator-supercapacitor modeling for low-voltage ride-through capability in DFIG-based wind turbines

Low-voltage ride-through is important for the operation stability of the system in balanced- and unbalanced-grid-fault-connected doubly fed induction generator-based wind turbines. In this study, a new LVRT capability approach was developed using positive-negative sequences and natural and forcing components in DFIG. Besides, supercapacitor modeling is enhanced depending on the voltage-capacity relation. Rotor electro-motor force is developed to improve low-voltage ride-through capability against not only symmetrical but also asymmetrical faults of DFIG. The performances of the DFIG with and without the novel active-passive compensator-supercapacitor were compared. Novel active-passive compensator-supercapacitor modeling in DFIG was carried out in MATLAB/SIMULINK environment. A comparison of the system behaviors was made between three-phase faults, two-phase faults and a phase-ground fault with and without a novel active-passive compensator-supercapacitor modeling. Parameters for the DFIG including terminal voltage, angular speed, electrical torque variations and d-q axis rotor-stator current variations, in addition to a 34.5 kV bus voltage, were investigated. It was found that the system became stable in a short time and oscillations were damped using novel active-passive compensator-supercapacitor modeling and rotor EMF.WOS:0004902298000022-s2.0-8507449521

The functional independence measure in spinal cord injured patients: Comparison of questioning with observational rating

Functional independence measure (FIM) is becoming widely used for all aspects of disabling diseases including spinal cord injury (SCI). It is recommended that it is rated by trained clinicians familiar with the patients. We aimed to compare the ratings of those patients who were questioned with those who were observed in a simulated environment

The thickness of the ligamentum flavum in relation to age and gender

Hypertrophy of the ligamentum flavum (LF) can reduce the diameter of the spinal canal posteriorly. Such stenosis may significantly compress the dural sac and nerve roots, resulting in symptoms, even without a bulging anulus fibrosus or herniated nucleus pulposus. We conducted an anatomical study to determine the influence of age and gender on the thickness of the LF at the lower lumbar levels using magnetic resonance imaging (MRI). The thickness of 1,280 ligaments was determined at the L4-L5 and L5-S1 levels from MRIs. We screened 320 patients (152 males [47.5%] and 168 females [52.5%]) between 21 and 82 years of age. There were no significant differences in LF thickness with respect to gender (P > 0.05). Age was not correlated with the thicknesses of the LF. The left LF at the L4-L5 and L5-S1 levels was significantly thicker than on the right side (P < 0.05). Furthermore, the LF thicknesses at L5-S1 bilaterally were significantly greater than on the corresponding sides at L4-L5 (P < 0.05). The LF is an important anatomical structure, which might cause low back or leg pain. Therefore, the thickness of the LF should be measured and evaluated carefully in the case of spinal stenosis. © 2009 Wiley-Liss, Inc

Symbiotic organisms search algorithm for economic load dispatch problem with valve-point effect

Symbiotic Organisms Search (SOS) is a brand new and effective metaheuristic optimization algorithm. This paper proposes the SOS algorithm to solve the Economic Load Dispatch (ELD) problem with valve-point effect, which is one of the essential optimization problems in modern power systems. The proposed algorithm is tested on five different test cases consisting of 3-machine 6-bus, IEEE 5-machine 14-bus, IEEE 6-machine 30-bus, and 13- and 40-unit test systems both with transmission loss and without transmission loss. These test cases show that SOS is able to converge on the global optima, successfully. Moreover, results obtained from the proposed algorithm are compared through different methods used in solving the ELD problem existing in the literature. According to these results, SOS produces the best values among all methods. (C) 2018 Sharif University of Technology. All rights reserved

TRAUMATIC SPINAL-CORD INJURIES IN ISTANBUL, TURKEY - AN EPIDEMIOLOGIC-STUDY

This is a retrospective study conducted in all of the hospitals of Istanbul to survey new patients with a traumatic spinal cord injury (SCI) in 1992. In that year 152 new traumatic SCI were identified. The estimated annual incidence was 21 per million population. The male/female ratio was 3/1. The mean age was 33, being 34 for male patients and 31 for female patients. 72% of all patients were under the age of forty. The major causes of SCI were falls (43%) and car accidents (41%), followed by being struck by an object (7%), gunshot injury (5%), stab injury (2%). Fifty patients (33%) were tetraplegic and 102 (67%) paraplegic. Regarding the tetraplegic patients the commonest level was C5, in those who were paraplegic L1. There were no cases at levels C1, T1 or T2. The commonest associated injury was head trauma, followed by fractures of an extremity (or extremities). Severe head trauma, as a major cause of death, may obscure the actual incidence of SCI in this study. Accidental falls (exceeding road accidents) were mostly due to falls from buildings and accidents on work premises