Voltage Dip mitigation in Distribution System by Using D-Statcom

A Power quality problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in a failure or a mis-operation of end user equipments. Utility distribution networks, sensitive industrial loads and critical commercial operations suffer from various types of outages and service interruptions which can cost significant financial losses. With the restructuring of power systems and with shifting trend towards distributed and dispersed generation, the issue of power quality is going to take newer dimensions. In developing countries like India, where the variation of power frequency and many such other determinants of power quality are themselves a serious question, it is very vital to take positive steps in this direction .The present work is to identify the prominent concerns in this area and hence the measures that can enhance the quality of the power are recommended. This work describes the techniques of correcting the supply voltage sag, swell and interruption in a distributed system. At present, a wide range of very flexible controllers, which capitalize on newly available power electronics components, are emerging for custom power applications. Among these, the distribution static compensator and the dynamic voltage restorer are most effective devices, both of them based on the VSC principle. A D-STATCOM injects a current into the system to correct the voltage sag, swell and interruption. Comprehensive results are presented to assess the performance of each device as a potential custom power solution The STATCOM is applied to regulate transmission voltage to allow greater power flow in a voltage limited transmission network, in the same manner as a static var compensator (SVC), the STATCOM has further potential by giving an inherently faster response and greater output to a system with depressed voltage and offers improved quality of supply. The main applications of the STATCOM are; Distribution STATCOM (D-STATCOM) exhibits high speed control of reactive power to provide voltage stabilization and other type of system control. The DSTATCOM protects the utility transmission or distribution system from voltage sag and /or flicker caused by rapidly varying reactive current demand. During the transient conditions the D-STATCOM provides leading or lagging reactive power to active system stability, power factor correction and load balancing Keywords: Distribution Static Synchronous Compensator (D-STATCOM), Voltage Dip, Distribution Syste

Operational Behaviour of a Complex System Under Priority Repair Echelons

A mathematical model is set up to evaluate the reliability of a complex system comprising two subsystems (with stand by redundancy in one subsystem). The failure and repair of units for both the subsystems follow exponential and general time distributions respectively. The switching over device for standby subsystem is not perfect and its repair is opportunistic. The repair for both subsystems is carried out under priority. The concept of waiting time for the repair of failed units in staidly subsystem has also been introduced. Supplementary variable and Laplace Transform techniques have been applied to obtain the transient state probabilities for such a system. From these pointwise availability has been evaluated. In the end, a particular case when repair follows exponential time distribution has been derived and asymptotic behaviour of such a system has also been examined

Assessing the Influence of Importance Prompt and Box Size on Response to Open-ended Questions in Mixed Mode Surveys: Evidence on Response Rate and Response Quality

To understand the thinking behind respondents’ answers, researchers occasionally use open-ended questions. Getting a quality response to open-ended questions can be challenging but attending to the visual design of the question and using a motivational statement in the question can increase item response and data quality. To understand the use of open-ended questions in surveys further, we designed an experiment testing the effect of an importance statement (present/absent) and box size (large/small) on item response rate and response quality in a mixed-mode (web and mail modes) survey. Data for the study came from a survey of Florida Cooperative Extension Service (FCES) clients. The results showed that item response was improved with the importance prompt, irrespective of box size. The combination of importance statement and larger answer box also resulted in more words. Web responses produced more words than those on paper and words counts were significantly improved with an importance prompt for web responses. Overall, the combination of importance prompt, larger box size and web mode was most important in producing the best item response rate and response quality in our mixed-mode survey

Comparative efficacy of agomelatine versus sertraline in major depressive disorder in Himalayan region of India

Background: Depression, a major common affective disorder which carries excess mortality through suicide. Among various drug classes available SSRI’s are usually a choice, but many patients show inadequate response, residual symptoms or discontinue medication due to intolerable side effects. Disturbances of circadian rhythm function are an etiopathogenic hallmark of depression. The degree of circadian misalignment correlates with the severity of depression and circadian abnormalities may partially be a consequence of alterations in behavior and sleep patterns that accompany depression. Agomelatine an agonist acts on MT1 and MT2 receptors and antagonist of 5HT2c receptors contributes to its resynchronization of circadian rhythms, enhancement of dopaminergic and adrenergic input to the frontal cortex, induction of hippocampal neurogenesis, and ultimately, to its antidepressant effect.Methods: The study was randomized, prospective, comparative and interventional regarding the efficacy of therapy. Hundred consenting patients of MDD attending psychiatry OPD were screened for possible enrollment into group A(Agomelatine) and group B(Sertraline). Patients were assessed by semi-structured case recording form, DSM-IV- TR Criteria for major depressive episode, Hamilton Rating Scale for Depression (HAM-D) and Clinical Global Impressions for severity (CGI-S) at baseline and CGI for improvement (CGI-I), every two weeks interval and final assessment at 8 weeks.Results: Socio-demographic parameters like age and sex distribution, marital status, locality, family type, educational status, occupation and socio-economic class were comparable between two groups. Similarly baseline HAM-D and CGI-S values between the two groups were statistically non-significant. HAM-D, CGI-S and CGI-I values at eight weeks among the two groups were also statistically non-significant but in all three sertraline had decreased the values to a greater extent and showed a trend towards improvement.Conclusions: Both groups had shown significant decrease in scores of all scales i.e. HAM-D, CGI-S, and CGI-I at the end of 8th week as compared to baseline scores, indicating that the uses of agomelatine and sertraline have resulted in significant improvement in symptoms of patients of MDD and reinforcing there efficacy in treatment of MDD. No statistical difference was observed between two groups.

Self-Identity of Biracial Children: What Role Do Parents Play?

One of the fastest growing student groups today is the biracial student population. This study is part of a larger exploratory descriptive study on biracial college students with a focus on the extent to which parents socialized their biracial children in the cultures of both parents while growing up and how these students chose to self-identify. Biracial students at a large, predominantly white, research university in the northeastern United States completed an online survey. Descriptive statistics and content analysis were used to analyze the data. The results indicated that most students had adopted a “border” identity. The majority of parents had encouraged their children to have an acceptance and pride in their biracial status. However, many students would have appreciated more exposure and knowledge of their heritages, as well as preparation for dealing with their environment as a biracial person. Students offered recommendations for parental practices to strengthen their racial identity

Metallic monoclinic phase in VO2_2 induced by electrochemical gating: in-situ Raman study

We report in-situ Raman scattering studies of electrochemically top gated VO$_2$ thin film to address metal-insulator transition (MIT) under gating. The room temperature monoclinic insulating phase goes to metallic state at a gate voltage of 2.6 V. However, the number of Raman modes do not change with electrolyte gating showing that the metallic phase is still monoclinic. The high frequency Raman mode A$_g$(7) near 616 cm$^{-1}$ ascribed to V-O vibration of bond length 2.06 \AA~ in VO$_6$ octahedra hardens with increasing gate voltage and the B$_g$(3) mode near 654 cm$^{-1}$ softens. This shows that the distortion of the VO$_6$ octahedra in the monoclinic phase decreases with gating. The time dependent Raman data at fixed gate voltages of 1 V (for 50 minute, showing enhancement of conductivity by a factor of 50) and 2 V (for 130 minute, showing further increase in conductivity by a factor of 5) show similar changes in high frequency Raman modes A$_g$(7) and B$_g$(3) as observed in gating. This slow change in conductance together with Raman frequency changes show that the governing mechanism for metalization is more likely to the diffusion controlled oxygen vacancy formation due to the applied electric field.Comment: 5 pages, 6 figure