Optimization Strategy of SVC for Eliminating Electromagnetic Oscillation in Weak Networking Power Systems

The central Tibet AC interconnection project (CTAIP), which connects the Tibet power grid and the Sichuan power grid through a long distance transmission line of more than 1400 km, has a significant problem of voltage regulation. In order to improve the voltage regulation performance, six sets of ±60 Mvar static VAR compensators (SVC) were installed in the CTAIP. However, the SVCs may lead to electromagnetic oscillation below 50 Hz while improving voltage regulation capability. In this paper, the electromagnetic oscillation modes and the sensitivity of control parameters of SVC are analyzed. Then, the characteristics and influencing factors of the oscillation are discussed. It was found that there is an inherent electromagnetic oscillation mode below 50 Hz in the ultra-long distance transmission system. The employ of SVCs weaken the damping of this mode. Large proportional gain and integral gain (PI) parameters of SVCs can improve the voltage regulation performance, but weaken the electromagnetic oscillation mode damping. Therefore, a suppression method based on SVC PI parameters optimization is proposed to damp the oscillation. The essential of this method is to use the rising time of voltage response and setting time of SVCs as performance indicators of voltage regulation, and take the damping level of the electromagnetic oscillation mode as the performance index of SVC electromagnetic oscillation suppression ability. Combining the two indicators to form a comprehensive optimization index function, an intelligent optimization algorithm is applied. The process of SVC parameter optimization and the steps of multi-SVC parameter optimization in large power grids is proposed. Finally, PSCAD and real-time digital simulation (RTDS) simulation results verified the correctness of the proposed method. The optimization strategy was applied to CTAIP. The artificial grounding short circuit experimental results proved the effectiveness of the proposed strategy.

Length Effect on the Stress Detection of Prestressed Steel Strands Based on Electromagnetic Oscillation Method

Prestress detection of structures has been puzzling structural engineers for a long time. The inductance–capacitance (LC) electromagnetic oscillation method has shown a potential solution to this problem. It connects the two ends of a steel strand, which is simulated as an inductor, to the oscillation circuit, and the stress of the steel strand can be calculated by measuring the oscillation frequency of the circuit through a frequency meter. In the previous studies, the authors found that stress-frequency relation of 1.2 m steel strand was negatively correlated, while the stress-frequency of 10 m steel strand was positively correlated. To verify this conflict, two kinds of electrical inductance models of steel strands were established to fit the lengths. With the models, the stress-frequency relations of steel strands with different lengths were analyzed. After that, two kinds of experimental platforms were set up, and a series of stress-frequency relationship tests were carried out with 1.2 m, 5 m, 10 m and 15 m steel strands. Theoretical analysis and experimental results show that when the length is less than 2.013 m, the stress and oscillation frequencies are negatively correlated; when length is more than 2.199 m, the stress and oscillation frequencies are positively correlated; while when length is between 2.013 m and 2.199 m, the stress-frequency relationship is in transit from negative correlation to positive correlation.

Possibilities of correction rheological blood svoytv at chipped and cut wounds of the breast

Цель - изучение влияния электромагнитных колебаний миллиметрового диапазона на реологические свойства крови у пациентов с колото-резаными ранениями груди с целью их коррекции. Методика. Изменение реологических свойств крови изучено у 22 пациентов с проникающими колото-резаными ранениями груди без повреждения внутренних органов в течение ближайшего послеоперационного периода. Всем больным были выполнены первичная хирургическая обработка и дренирование плевральной полости. У всех пациентов объем кровопотери составил 200-500 мл. Критериями включения были: наличие проникающего ранения грудной клетки, наличие малого гемоторакса. Критериями исключения: наличие кровопотери более 500 мл, наличие сочетанных и множественных повреждений. Основная группа разделена на 2 подгруппы, в 1-ю вошли 12 пациентов с применением электромагнитных колебаний миллиметрового диапазона, во 2-ю - 10 человек без применения данного воздействия. Группу сравнения составили 15 относительно здоровых доноров-добровольцев сопоставимых по возрасту и полу. Всем пациентам не проводилась гемотрансфузия, объем инфузионной терапии был сопоставим в обеих группах. Изменения реологии крови выявлялись с помощью учета вязкости крови, изменения индекса деформации и агрегации эритроцитов. Заключение. Установлено, что применение электромагнитного колебания миллиметрового диапазона у пациентов с колото-резаными ранениями груди предотвращает развитие изменений реологических свойств крови, при этом пациенты хорошо переносят данную процедуру, что проявляется отсутствием побочных эффектов. The purpose: research objective: to study influence of electromagnetic oscillations of millimetric range on rheological properties of blood at patients with chipped and cut wounds of a breast for the purpose of their correction. Methods. For the solution of a research objective we have carried out studying of changes of rheological properties of blood at the 22nd patient with the getting chipped and cut wounds of a breast without internal injury during the next postoperative period. All patient has executed primary surgical processing and drainage of a pleural cavity. At all patients the volume of blood loss has made 200-500 ml. Criteria of inclusion were: existence of the getting wound of a thorax, existence of a small gemotoraks. Criteria of an exception: blood loss existence more than 500 ml, existence of the combined and multiple damages. The main group is divided into two subgroups, in the first 12 patients with application of electromagnetic oscillations of millimetric range, have entered the second 10 people without application of electromagnetic oscillations of millimetric range. The group of comparison was made by 15 rather healthy donor volunteers of the same age and a floor. To all patients the hemotransfusion wasn’t carried out, the volume of infusional therapy was comparable in both groups. Changes of a rheology of blood came to light by means of the accounting of viscosity of blood, change of an index of deformation and aggregation of erythrocytes. Conclusion. As a result of the conducted research it is established that application of electromagnetic oscillation of millimetric range for patients with chipped and cut wounds of a breast prevents development of changes of rheological properties of blood, at the same time patients well transfer this procedure that is shown by lack of side effects.

Coupling between two kinds of band gaps of a shunted tube piezoelectric phononic crystal

A tube-type piezoelectric phononic crystal model is proposed to study interaction between locally resonant and Bragg band gaps, which is arrayed periodically by metal and piezoelectric segments. Each piezoelectric segment consists of a shell with series-connected and opposite directions polarized double layers and a resonant shunting circuit. According to the interaction between Bragg scattering and local electromagnetic oscillation, three regions corresponding to the inductance can be divided as follows: quasi-short circuits region, coupling region, and quasi-open circuits region. Some interesting phenomena are found from the coupling between Bragg scattering and locally resonant of electromagnetic oscillation. (1) In the coupling region, a pass band splits a Bragg band gap into two band gaps. But the cut-off frequency of the second band gap does not change with the inductance. (2) In the quasi-open circuits region, Bragg and locally resonant band gaps exist independently. (3) The first band gap transits from Bragg scattering to local resonance when the inductance increases from quasi-short circuits region to quasi-open circuits region. (4) The cut-off frequency of the first band gap is always less than the estimated resonant frequency of inductor-capacitor oscillators. Finally, the theoretical result is validated by two kinds of finite element models based on ANSYS.