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The article discusses issues related to ensuring secure operation of the National Power System. The tasks of transmission system operators in that scope were presented and the power demand of the Polish National Power System on critical days in terms of power generation and demand was characterized. The article also presents the causes and course of events which took place in August 2015 when there was a critical imbalance in the Polish National Power System leading to the introduction of limitations. Then, the possibilities and types of costs connected with the possibilities of balancing the system in the periods of peak loads were characterized. The summary of the article contains the presentation of conclusions related to power balancing in the power system and reduction of related costs.

This paper provides an example of the application of the acoustic emission (AE) method for the diagnosis of technical conditions of a three-phase on-load tap-changer (OLTC) GIII type. The measurements were performed for an amount of 10 items of OLTCs, installed in power transformers with a capacity of 250 MVA. The study was conducted in two different OLTC operating conditions during the tapping process: under load and free running conditions. The analysis of the measurement results was made in both time domain and time-frequency domain. The description of the AE signals generated by the OLTC in the time domain was performed using the analysis of waveforms and determined characteristic times. Within the time-frequency domain the measured signals were described by short-time Fourier transform spectrograms. [ABSTRACT FROM AUTHOR]

Objective: Here, we retrospectively investigate the value of voxel-wisely plotted diffusion tensor-derived (DTI) axial, radial and mean diffusivity for the early detection of malignant transformation (MT) in WHO II glioma compared to contrast-enhanced images. Materials and Methods: Forty-seven patients underwent brain magnetic resonance imaging follow-up between 2006–2014 after gross-tumor resection of intra-axial WHO II glioma. Axial/Mean/Radial diffusivity maps (AD/MD/RD) were generated from DTI data. ADmin/MDmin/RDmin values were quantified within tumor regions-of-interest generated by two independent readers including tumor contrast-to-noise (CNR). Sensitivity/specificity and area-under-the-curve (AUC) were calculated using receiver-operating-characteristic analysis. Inter-reader agreement was assessed (Cohen’s kappa). Results: Eighteen patients demonstrated malignant transformation (MT) confirmed in 8/18 by histopathology and in 10/18 through imaging follow-up. Twelve of 18 patients (66.6%) with MT showed diffusion restriction timely coincidental with contrast-enhancement (CE). In the remaining six patients (33.3%), the diffusion restriction preceded the CE. The mean gain in detection time using DTI was (0.8±0.5 years, p = 0.028). Compared to MDmin and RDmin, ROC-analysis showed best diagnostic value for ADmin (sensitivity/specificity 94.94%/89.7%, AUC 0.96; p<0.0001) to detect MT. CNR was highest for AD (1.83±0.14), compared to MD (1.31±0.19; p<0.003) and RD (0.90±0.23; p<0.0001). Cohen’s Kappa was 0.77 for ADmin, 0.71 for MDmin and 0.65 for RDmin (p<0.0001, respectively). Conclusion: MT is detectable at the same time point or earlier compared to T1w-CE by diffusion restriction in diffusion-tensor-derived maps. AD demonstrated highest sensitivity/specificity/tumor-contrast compared to radial or mean diffusivity (= apparent diffusion coefficient) to detect MT. [ABSTRACT FROM AUTHOR]

Background: Assessment of the relationship between preoperative neurological deficits and diffusion tensor imaging (DTI) parameters in patients with brain tumour within/adjacent to pyramidal tract and motor cortex. Evaluation of the difference in fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values in patients with low and high grade gliomas. Material and Metthods: 20 patients with supratentorial brain tumours were divided into two groups: I with preoperative neurological deficits and II without preoperative neurological deficits. 8/20 tumours were classified as low grade gliomas, 10/20 as high grade gliomas and 2/10 as metastases. All MR examinations were performed on a 3T scanner . FA and ADC values were calculated for a precentral gyrus (PCG), a posterior limb of the internal capsule (PLIC) and a pyramidal tract (PT) ipsilateral and contralateral to the tumour side. These values were compared between patients with and without preoperative neurological deficits, with low and high grade gliomas. Results: A statistical analysis revealed significant differences between patients with and without preoperative neurological deficits in PCGs and PTs ipsilateral to the tumour side. Separate analysis conducted in the group with preoperative neurological deficits showed significant statistical differences only in terms of FA values comparing ipsilateral and contralateral tumour side. No statistically significant difference was observed comparing FA and ADC values ipsilateral and contralateral to the tumour side in the group without preoperative neurological deficits and between patients with low and high grade gliomas. Conclusions: There is a relation between FA and ADC values and preoperative deficits in patients with brain tumour adjacent/within the main white matter tracts. Tumour relation to the white matter tracts is more important than the glioma WHO grade. [ABSTRACT FROM AUTHOR]

The core objective of transmission tariffs is the recovery of costs related to the transport of electricity. A usual component of a tariff is a fixed charge that covers the costs of the network infrastructure. As many customers use the power grid, the rate of this charge should reflect, as closely as possible, the actual costs of supplying energy to the individual consumers. These costs result from which network elements have been used in delivering the electricity, and to what extent these elements have been used. Therefore, the fixed transmission rates should depend on the degree of network utilization. This article investigates definitions of the degree of network utilization based on the active power flow. To calculate the degree of network utilization, the flow of electricity on a branch must be decomposed into the streams flowing to individual customers. For this decomposition, two methods are examined: a power flow tracing method, based on the proportional sharing principle, and an incremental power flow method, based on the superposition principle. The analyzed methodology is applied to a small test system for conceptual discussions, as well as to the transmission network of the Polish power system, as an example of practical application. The results of this study were then compared with the commonly used "postage stamp" method. Finally, several practical aspects related to the potential implementation of the presented methodology are discussed. [ABSTRACT FROM AUTHOR]

The balancing of the power of the Polish Power System (KSE) is a key element in ensuring the safety of electric energy supplies to end users. This article presents an analysis of the power demand in power systems (PS), with emphasis on the typical power variability both in subsequent hours of the day and on particular days and in particular months each year. The methodology for calculating the costs of electric energy undelivered to the end users and the amount of these costs for KSE is presented. Different possibilities have been analyzed for balancing power systems' peak load and assumptions have been formulated for calculating the amount of the related costs. On this basis, a comparative analysis has been made of the possibility to balance peak load using operators' system services, trans-border connections, and various energy storage solutions. On the basis of the obtained results, optimal tools have been proposed for market-based influence from transmission and distribution system operators on energy market participants' behaviors in order to ensure the power systems' operating safety and continuous energy deliveries to end users. [ABSTRACT FROM AUTHOR]

Abstract: Objective: A prospective volumetric analysis of extent of resection (EOR) was carried out to assess surgical outcomes in adults diagnosed with hemispheric low grade gliomas (LGGs). Materials and methods: 68 consecutive patients diagnosed with LGGs were enrolled in the study. Pre- and post-operative tumor volumes and EOR were measured based on FLAIR MRI. Dynamic susceptibility contrast perfusion magnetic resonance imaging (DSC MRI) was used for the assessment of relative cerebral blood volume (rCBV). Three outcome measures were assessed: overall survival (OS), progression-free survival (PFS), and malignant degeneration-free survival (MFS). Results: In 6 (9%) patients permanent neurologic deficits were observed. No statistically significant dependence between the EOR and the occurrence of permanent deficits was found. The eloquent or close to the eloquent location was statistically connected with lower EOR (p =0.023). The preoperative volume of tumors treated with gross total resection was significantly smaller than the volume of tumors in subtotal or partial resection groups (p =0.020, p <0.001, respectively). OS was predicted by age at diagnosis (p =0.032), and rCBV (p =0.002). Progression and malignant transformation occurred in 22 (32%) and 11 (16%) out of 68 patients. PFS was predicted by preoperative tumor volume (p =0.005), postoperative tumor volume (p =0.008), the EOR (p =0.001), and by the rCBV (p =0.033). MFS was predicted by preoperative tumor volume (p =0.034), the EOR (p p =0.020), and by rCBV (p =0.022). Postoperative tumor volume was associated with a trend of improved MFS (p =0.072). The univariate analysis shows the statistical trend for the relationship between histological subtype and PFS and MFS (p =0.079, p =0.078, respectively). Multivariate analysis selected preoperative tumor volume and rCBV as independently associated with PFS (p =0.009, p =0.019, respectively) and MFS (p =0.023, p =0.035, respectively). EOR was associated with a trend of improved PFS, and MFS (p =0.069, p =0.094, respectively). Conclusions: Tumor resection of LGG with the use of intraoperative monitoring and neuronavigation is associated with a low risk of new permanent deficits, but EOR significantly decreases with the size of the tumor and/or its location in/close to the eloquent areas. Smaller preoperative tumor volume and greater EOR are significantly associated with longer OS, PFS and MFS. Preoperative rCBV is one of the important prognostic factors significantly connected with survival. Prognosis in LGGs is still under discussion. Other factors such as age, histopathological subtype and KPS should not be underestimated. [Copyright &y& Elsevier]