Harmonic resonance is an important factor to be considered in a power transmission networks during connection of remote generation units with high-voltage cables (e.g. wind or solar power plants ...etc.). It is known that cable characteristics differ from characteristics of conventional overhead lines. Cable capacitance is far higher than capacitance of an equivalent overhead line, what can potentially lead to the low resonant frequencies which may be triggered by various switching events, such as transformer or shunt reactor energization etc. In this paper, possible consequences of power plant connection to transmission network with long HVAC cable are analysed, with regard to harmonic resonance and frequency response of the network. The research has been conducted on developed model of the power transmission network in the software for calculation of electro-magnetic transients EMTP-RV.
•An overview on transformer “Black box” modeling.•A procedure for measuring the admittance matrix of a transformer with FRA equipment.•Unconstrained fitting methods (post processing passivity ...enforcement).•Constrained fitting methods (enforcing passivity during the fitting).•Comparison of accuracy of different fitting methods.
Traditional transformer models available in EMTP-like software packages are not capable of representing transformer behavior during a transient state, which includes high frequencies, since they usually do not adequately take into account the transformer resonant behavior caused by its highly complicated design. Therefore, more complex “Black box” models are developed. Those models can be established without any knowledge of transformer geometry, based on the fitting of the measured admittance matrix of the transformer versus frequency. Unfortunately, the measurement and exploitation of a transformer's admittance matrix are not straightforward. The existing fitting methods include solving a non-convex constrained problem. Hence, it is not always easy to find an optimal solution of the problem. The difficulties, which can arise when building a high frequency “Black box” transformer model, are described in this paper together with a comparison of the performance and fitting accuracy of different numerical packages.
•Current distribution in the electric traction system.•Modeling of electric traction system 25kV, 50Hz.•Calculation of induced voltage on sensitive telecommunication line.•Current distribution in ...case of lightning stroke to contact network.
Current distribution in the electric traction system is an important factor regarding the electromagnetic influences on the surrounding metallic structures. The current value directly determines the magnetic field and consequently coupling of the systems. A single rail traction system can be equipped with return conductor. The return current flowing through return conductor has an opposite direction of supply current and decreases coupling and interferences.
This paper presents the AC current distribution for both designs, with and without return conductor. Also, the soil resistivity is varied. The higher the soil resistivity, the higher is the amount of return current in rails and return conductor. The different construction of return conductor results in different impedance of return path. The relations of return conductor construction and return current value are analysed.
Lightning can directly impact different traction system elements such as contact network, tower or return wire. The current distributions in several cases of lightning impacting different traction system elements are presented.
•Transformer model based on limited information about the transformer geometry.•Complex permeability equivalence principle.•Transformer nodal frequency dependence admittance matrix.•Verification ...based on lightning impulse tests measurements.
To represent transformer behaviour during a transient state which includes high frequencies, it is necessary to consider the resonances which occur inside the transformer. One strategy is to deduce the transformer model from the measurements of the transformer’s frequency response, another one is to construct the model based on a careful representation of the inside of the apparatus.
In the paper a model is presented which is compatible with EMTP-type software programs based on a finite element method (FEM) calculations and the complex permeability approximation. The model can be classified as a Grey Box transformer model, according to the terminology of the CIGRE. The model’s frequency dependent parameters are derived from limited information about the transformer geometry. State space equations are used to input the model into an electromagnetic transient calculation software program. This approach requires specific mathematical treatments to avoid stability issues during simulations. The model is validated for lightning impulse studies using the field test measurements of over-voltages that had occurred at the external transformer’s terminals.
Left ventricular non-compaction (LVNC) is a rare cardiomyopathy, which is today, due to modern ultrasound technology more frequently detected in clinical practice. It is caused by the failure of ...normal embryonic development of the myocardium from loosely arranged muscle fibers to the mature compacted form of myocardium. Morphologic presentation consists of unique two-layered structure, a thick noncompacted endocardial and a thin compact epicardial layer, in infero-lateral and apical segments. The endocardial layer contains loosely arranged muscle fibers, prominent trabeculations and deep perfused intertrabecular recesses. It could be diagnosed both as an infantile or adult type, appearing sporadically or among families where it is transferred x-linked or autosomal dominant. The recognition of the disease is mandatory because of its high mortality and morbidity due to the progressive heart failure, thromboembolic events and lethal arrhythmias. Echocardiography is the procedure of choice to confirm the diagnosis and in the follow-up of patients with LVNC. A literature review about LVNC pathogenesis, diagnostis, and treatment was discussed.
Type III transforming growth factor (TGFβ) receptor (TGFβrIII) modulates TGFβ superfamily signaling. Its tumor tissue expression is downregulated in human breast cancer. We determined (indirect ...ELISA) plasma levels of the soluble receptor (sTGFβrIII) in 47 women with breast cancer (AJCC stages 0-IIB) (cases) pre-surgery and over two months after the surgery, and in 36 healthy women (controls). Plasma sTBFβrIII was lower in cases than in the controls (age-adjusted difference −29.7 ng/mL, p < 0.001), and discriminated between disease and health (sensitivity and specificity 100% at 16.6 ng/mL). With adjustment for age, AJCC stage, lymph node involvement, HER2 and hormone receptor status, higher pre-surgery sTBFβrIII was associated with better progression-free survival (HR = 0.68, 95%CI 0.49-0.89, p = 0.004). An increasing trend in plasma sTBFβrIII was observed over 2 months after the surgery (0.6% increase/day, p < 0.001), consistently across the patient subsets. Data suggest a high potential of plasma sTBFβrIII as a novel diagnostic and prognostic biomarker in breast cancer.
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