Power system security enhancement by HVDC links using a closed-loop emergency control

In recent years, guaranteeing that large-scale interconnected systems operate safely, stably and economically has become a major and emergency issue. A number of high profile blackouts caused by cascading outages have focused attention on this issue. Embedded HVDC (High Voltage Direct Current) links within a larger AC power system are known to act as a “firewall” against cascading disturbances and therefore, can effectively contribute in preventing blackouts. A good example is the 2003 blackout in USA and Canada, where the Québec grid was not affected due to its HVDC interconnection. In the literature, many works have studied the impact of HVDC on the power system stability, but very few examples exist in the area of its impact on the system security. This paper presents a control strategy for HVDC systems to increase their contribution to system security. A real-time closed-loop control scheme is used to modulate the DC power of HVDC links to alleviate AC system overloads and improve system security. Simulations carried out on a simplified model of the Hydro-Québec network show that the proposed method works well and can greatly improve system security during emergency situations.Peer reviewedFinal Accepted Versio

Cyto-histological correlation in diagnosis of gastrointestinal lesions- a prospective study in a tertiary care institute

Background: Gastrointestinal tract is involved by a large number of inflammatory, infectious and neoplastic diseases. There is a worldwide rising incidence of GIT lesions especially neoplasms.Methods: This study was planned to correlate endoscopic and colonoscopic brush cytology with histopathology of gastrointestinal lesions and to determine the spectrum of gastrointestinal lesions in patients subjected to endoscopic brushings and biopsy.Results: Sensitivity of upper GI brush cytology was 95.15% and specificity 90.41%. Sensitivity of colonoscopic brush cytology was 100% and specificity 86.79%. The accuracy of brush cytology came out to be 92.45% in upper GIT and 92.22% in lower GIT.Conclusions: Brush cytology is a non-invasive and cost-effective method to retrieve epithelial cells from a much larger surface area of the mucosa, thus allowing thorough sampling and increasing the diagnostic yield

Quantitative computed tomography (CT) assessment of emphysema in patients with severe chronic obstructive pulmonary disease (COPD) and its correlation with age, sex, pulmonary function tests, BMI, smoking, and biomass exposure

Background: To evaluate the role of HRCT in quantifying emphysema in severe COPD patients and to study the variations in the pattern of emphysema in relation to age, sex, FEV1, smoking index, biomass exposure, and BMI. Material/Methods: Automatic lung segmentation of HRCT scans in 41 severe COPD patients (GOLD stage III or more) was done using an emphysema protocol. The extent of emphysema was assessed using the density mask method with a threshold of -950 HU (%LAA-950). The percentage of emphysema in each lung lobe and both lungs was correlated with 6 parameters - age, sex, BMI, smoking index, biomass exposure, and FEV1. Results: Smoking resulted in homogenously distributed emphysema regardless of the severity of smoking. BMI was inversely correlated with the extent of emphysema. A significant association was found between the percentage of emphysema in the right lower lobe and BMI (P=0.015), between biomass exposure and the percentage of emphysema in RUL, RLL, and both lungs (P values of 0.024, 0.016, and 0.036, respectively). The extent of emphysema was disproportionately low compared to the amount of obstruction on PFTs, indicating an airway predominant variety of COPD with significant biomass exposure. Conclusions: Smoking is associated with a relatively homogenous distribution of emphysema with no regional predilection. Biomass exposure produces predominantly right-sided emphysema. BMI decreases with increasing levels of emphysema in the right lower lobe. These risk factors of emphysema patterns are helpful in deciding on the management, including surgical options

The Bethesda system for reporting thyroid cytology: a prospective study in a tertiary care institute along with review of literature

Background: The Bethesda system for reporting thyroid cytology (TSBRTC) was devised by the National Cancer Institute (NCI) to obtain uniformity, reproducibility and a defined management protocol while dealing with thyroid lesions. This study was undertaken with the aim to see the benefits of adopting TBSRTC in the diagnosis of thyroid FNAC, and identify the malignancy risk of each category.Methods: This cross-sectional study was conducted in Indira Gandhi Medical College, Shimla, Himachal Pradesh from June 2016 to July 2017 on 181 thyroid FNACs which were reported according to the Bethesda system for reporting thyroid cytopathology (TBSRTC) under six categories: (I) non-diagnostic/unsatisfactory (II) benign (III) atypia of undetermined significance/follicular lesion of undetermined significance (IV) follicular neoplasm/suspicious for follicular neoplasm (specify if Hurthle cell (oncocytic) type (V) suspicious for malignancy (VI) malignant. Histopathological diagnosis was available for 65 cases where thyroidectomy was performed. Malignancy risk was calculated for each category. Sensitivity, specificity, positive and negative predictive values for TBSRCT were also calculated. All the data was analyzed in SPSS software version 22.0 (IBM, USA).Results: Benign lesions constituted the major bulk. After the use of TBSRTC, there was increased ability to look for follicular neoplasms, improvement in making definitive diagnosis of the cases, an improvement in diagnostic accuracy, and we were in line with the implied risk outlined by TBSRTC in most of the cases.Conclusions: Application of TBSRTC results in uniformity in reporting among pathologists and better interdisciplinary communication and patient management

Dynamic measurements of the wind power impact on power system inertia and stability

The integration of wind power generation (WPG) have many different impacts on the current power transmission and distribution systems. Most of them are related to their effect on the dynamic behaviour and frequency deviation during system frequency disturbances affecting the system inertia response. Different approaches have been presented to show the dynamic behaviour diminution, and several metrics have been proposed to quantify the impact of the inertia reduction. This scientific paper looks at the background system inertia problem, presenting some of the most significant contributions in observation of power system dynamic under high penetrations of WPG and presents two dynamic measurements. First one measures the damping ratio of the power lines quantifying it in an online fashion. The second one measures the frequency of an electrical power signal. The dynamic measurements are tested in a hypothetical active power signal with the inclusion of wind energy showing the affectivity of the dynamic measurements presented and the impact of wind farms in power systems. Finally, future work and conclusions are given

Jaundice in adult patients above 50 years of age: a comparative study of liver function tests

Background: Diagnosis of jaundice involves a range of tests. The liver function tests are done in all to arrive at a diagnosis and then manage the case appropriately. With advancing age, the incidence of liver disease increases. Understanding these changes is important for the management of liver diseases in the elderly. We conducted this study to find the difference in mean levels of Liver enzymes in younger and older age group of patients suffering with jaundice.Methods: It was a prospective observational study. All patients admitted with jaundice in the medicine ward satisfying inclusion/exclusion criteria were enrolled. The results of liver function tests in younger age and older age participants were then compared.Results: Total 100 participants were enrolled during the study period. 53 were enrolled in group one and the rest in group two. Anorexia (90%) was the most common symptom followed by abdominal distension (54%). The total bilirubin (8.8±4.7) as well as conjugated bilirubin (3.4±2.8) were higher in group one though they were not significant statistically (p=0.10 and 0.25 respectively). Mean AST and ALT levels were much higher in group 1 and statistically significant (p values <0.004 and 0.002 respectively). Conversely the mean PT values were higher in group two (p=0.02).Conclusions: Although the symptom severity may be more in elderly, the LFTs are not deranged proportionately. So there is a need to devise separate cut offs and these have to be lower for the older age group patients with jaundice. More studies with larger sample size are required to confirm the results

Evaluation of the synthetic inertia control using active damping method

The current and massive deployment of non-synchronous generation is degrading the inertial response in power systems. The addition of an extra control loop, the so-called synthetic inertia, can contribute in the improvement of the frequency response, through an additional power injection. In this paper, the active damping method is used to enhance both, the closed-loop current control and the synthetic inertia control loop. A full aggregated model of a wind turbine generator (WTG) is integrated in a test system. The results obtained show an increase in the power injected into the grid, thereby improving the frequency response after a frequency disturbance. Moreover, the response of the closed current-control loop and voltage loop are presented, in order to show their interaction with the synthetic inertia control

The TRV improvement of fast circuit breakers using solid-state series superconducting reactor

Utilizing superconducting technology in fault current limiters for power grid applications is a practical solution to achieve a more modern and efficient power system. This is due to their low-loss profile, high efficiency, and ability to transmit about 5x more power in the same footprint compared to conventional counterparts. In addition, the integration of renewable energy resources into power grids makes the use of fast circuit breakers essential. However, the Transient Recovery Voltage (TRV) of fast mechanical circuit breakers stays a concern. This paper studies the TRV of a fast circuit breaker during a fault condition. Then the effect of a solid-state superconducting series reactor (SSSR) on the TRV of the circuit breaker is investigated and compared using an analytical model, simulation studies, and experimental testing. The results prove that an SSSR significantly diminishes the TRV of the fast breaker and offers an effective superconducting solution for modern power grids