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Partial discharge (PD) detection is a standardized technique to qualify the insulation condition in power equipment. The main purpose of the article is to evaluate the performance of an extra high-sensitivity adapted giant magneto-resistive (xMR) sensor for non-contacting PD detection. First, compensation and signal conditioning circuits of the sensor are designed. Frequency response and time-domain response to fast calibrator pulses of the sensor with the implemented circuit are measured. Besides, PD experiments based on corona and surface models are carried out and compared with measurements using a high-frequency current transformer (HFCT). The results show that the xMR system can measure the magnetic fields produced by the PDs at distances up to 50 cm. The correlation between the HFCT and xMR signals is proportional under different voltages, showing that PDs can be effectively detected and evaluated by this method. PDs in a cross-linked polyethylene (XLPE) cable with an artificial discharging defect are successfully measured, demonstrating the sensitivity and performance of the xMR system., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage, ESP LAB, EEMS - General, High Voltage Technology Group

Partial discharges (PD) detection is an effective diagnostic method to assess the insulation condition of electrical power equipment in the high-voltage laboratory or field tests. This paper presents a non-contacting PD detection method for power equipment. The method is based on an extra high-sensitivity adapted giant magneto-resistive (xMR) sensor that measures the magnetic field produced by the PD currents. Firstly, this paper describes the sensor’s relevant principle and signal conditioning circuit. Next, the sensor’s typical performance, including the frequency response and time-domain response to calibrator PD pulses, is measured and compared with our previous work. The results indicate that the xMR system’s bandwidth is improved to the MHz range. Finally, PD experiments are carried out and compared with measurements using a commercially available high-frequency current transformer (HFCT), which allows for verification of the coherence of the results concerning the PD pulses and phase-resolved PD (PRPD) patterns. The results show that PD in a cross-linked polyethylene (XLPE) cable or a gas-insulated system (GIS) with artificial discharging defects is successfully measured, demonstrating the sensitivity and performance of the xMR system for PD detection., DC systems, Energy conversion & Storage, ESP LAB, EEMS - General, High Voltage Technology Group

Contains fulltext : 229201.pdf (Publisher’s version ) (Closed access), AIMS: In the SCALAF trial, catheter-based pulmonary vein isolation (PVI) was as effective in long-term prevention of atrial fibrillation (AF) as minimally invasive thoracoscopic PVI and left atrial appendage ligation (MIPI). Catheter ablation (CA) resulted in significantly less major complications as compare to MIPI. We report quality of life (QOL) outcome in these patients. METHODS: In this study, 52 patients with symptomatic paroxysmal or early persistent AF were randomized to either MIPI or CA. QOL was assessed at baseline, 3, 6, and 12 months follow-up using the SF-36 Health Survey Questionnaire. AF-related symptoms were quantified at each follow-up visit using the European Heart Rhythm Association (EHRA) score. RESULTS: Median age was 57 years and 78% was male. Paroxysmal AF was present in 74%. At 3 months follow-up, physical role limitations (88.2 +/- 29.5; versus 40.9 +/- 44.0; P = 0.001, respectively) and bodily pain scores (95.5 +/- 8.7; versus 76.0 +/- 27.8; P = 0.021, respectively) were significantly higher after CA compared to MIPI, indicating less limitation in daily activity caused by physical problems and less pain after CA than after MIPI. AF symptoms assessed by the EHRA scores improved significantly at 3, 6, 12, and 24 months compared to baseline in both treatment groups (P < 0.001), with no significant differences between treatment groups. CONCLUSIONS: CA and MIPI ablation of AF both resulted in an improvement in several QOL measurements, although CA resulted in significantly less physical problems and bodily pain 3 months after treatment compared to MIPI. CLINICAL TRIAL NUMBER: ClinicalTrials.gov identifier: NCT00703157.

In practice, High-voltage (HV) cables are occasionally exposed to impulse and superimposed transient conditions, which may initiate partial discharges (PD) temporarily. Whether such PDs persist under AC voltage after the transient conditions have vanished, is at focus in the research described in this paper. Since for cross-linked polyethylene (XLPE) cables the accessories are weak links in the HV cable insulation system, we investigated the PD behavior of an artificial joint defect in a HV cable model under impulse and superimposed voltages. By applying a dedicated PD measuring system it was found that, the impulse and superimposed voltages can initiate PD in the artificial defect, which under local electrical field conditions can persist for some time. The different parameters of the applied voltages have different effects on the PD behavior., DC systems, Energy conversion & Storage, EEMCS - General

This article contains the development of the Health Index (HI) and the Risk Assessment (RA) models for Gas Insulated Switchgear (GIS) operating under tropical conditions. A case study of 631 bays of GIS in tropics with service time from 1 up to 30 years is used during the development of the models. The basis for the HI model is the condition assessment of subsystems in GIS. This assessment translates the measured parameters from GIS subsystems into condition status based on a set of norms and rules. The condition status is presented in a score, where the non-linear scaling is chosen as it allows the poor parameters to really stand out. On the other hand, the RA model calculates the risk of a GIS major failure. The Total Failure Probability (TPF) unifies six risk indicators of GIS failures under tropical conditions. The risk may fall into one of the four categories, namely: Low, Medium, High, and Very High., DC systems, Energy conversion & Storage, EEMCS - General

Humid insulating gas (SF6) has been observed in a case study of 631 CB-bays of Gas Insulated Switchgear (GIS) operating under tropical conditions. The routine gas quality check in the case study reported that 20% of the non-Circuit Breaker enclosures have humidity above the value recommended by the IEEE and IEC standards. Therefore, an investigation into the flashover characteristics of a spacer in humid SF6 has been initiated in the High Voltage Laboratory of TU Delft, The Netherlands. The setup is a small model resembling the insulation system of a GIS with controlled parameters of humidity content and gas pressure. The electrical stresses in the test are AC, LI+, LI−, and SI with homogeneous, quasi-homogeneous-, and inhomogeneous field configurations. In general, the humidity does not influence the withstand strength of the spacer as long there is no condensation. When condensation occurred, the flashover voltage dropped by 28% during the test under AC at 2.6 bars, and by 38% during the test under LI+ at 2.5 bars; both with quasi-homogeneous field configuration. In the test with homogeneous field setup, the flashover voltage was dropped by 67% under LI+ at 3.4 bars. In our setup, it has also been observed that the flashover-drop due to condensation is higher than due to a 2-mm aluminum particle attached to the sample close to the high electric field region simulating the inhomogeneous field configuration., DC systems, Energy conversion & Storage, EEMCS - General

A partial discharge (PD) measuring system has been deployed in order to identify and measure PD in a high voltage (HV) cable joint under impulse and superimposed voltages under laboratory conditions. The challenge is to enable the detection of PD during the impulse conditions. The method of measurement has been investigated by introducing an artificial defect in the cable joint in a controlled way to create conditions for partial discharges to occur. Next the HV cable system is subjected to AC, impulse and superimposed voltage. Two high frequency current transformers (HFCT) installed at both ends of the cable joint were used to identify PD from the cable joint and to separate PD from disturbance. Transient voltage suppressors and spark gaps are applied to protect the measuring equipment. Band pass filters with selected characteristics are applied to suppress transient disturbances and increase the chance to detect PD during the impulse. PD signals are separated from transient disturbances during data post processing and by means of pulse polarity analysis. The developed system enables the detection of so-called main and reverse discharges respectively occurring during the rise and tail time of the superimposed impulse. The measurement results obtained show the effectiveness of the presented PD measuring system for investigating the effects of voltage transients on a HV cable system in laboratory conditions., DC systems, Energy conversion & Storage, ESP LAB, EEMCS - General

In practice, cross-linked polyethylene (XLPE) power cables can be subjected to alternating voltage with superimposed impulse transients. Such impulse transients may initiate partial discharges (PD) in insulation defects even below AC inception voltage. An initiated PD may persist under AC, which will cause insulation degradation. This paper investigates the PD behavior in MV XLPE cable accessories under impulse transients. Different scenarios of PD behavior are measured, described and analyzed. Based on the results, the effects of impulse transients on PD are summarized., DC systems, Energy conversion & Storage, EEMCS - General

Contains fulltext : 200354.pdf (Publisher’s version ) (Closed access), BACKGROUND: Current guidelines recommend both percutaneous catheter ablation (CA) and surgical ablation in the treatment of atrial fibrillation, with different levels of evidence. No direct comparison has been made between minimally invasive thoracoscopic pulmonary vein isolation with left atrial appendage ligation (surgical MIPI) versus percutaneous CA comprising of pulmonary vein isolation as primary treatment of atrial fibrillation. We, therefore, conducted a randomized controlled trial comparing the safety and efficacy of these 2 treatment modalities. METHODS: Eighty patients were enrolled in the study and underwent implantable loop recorder implantation. Twenty-eight patients did not reach randomization criteria. A total of 52 patients with symptomatic paroxysmal or early persistent atrial fibrillation were randomized, 26 to CA and 26 to surgical MIPI. The primary end point was defined as freedom of atrial tachyarrhythmias, without the use of antiarrhythmic drugs. The safety end point was freedom of complications. RESULTS: Median age was 57 years (range, 37-75), and 78% were men. Paroxysmal atrial fibrillation was present in 74%. Follow-up duration was >/=2 years in all patients. CA was noninferior to MIPI in terms of single-procedure arrhythmia-free survival after 2 years of follow-up (56.0% versus 29.2%; HR, 0.56; 95% CI, 0.26-1.20; log-rank P=0.059). Procedure-related major adverse events occurred significantly more often in MIPI than CA (20.8% versus 0%; P=0.029). CONCLUSIONS: Percutaneous pulmonary vein isolation was noninferior to MIPI in terms of efficacy and resulted in less complications. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov . Unique identifier: NCT00703157.

Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm−1. In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm−1; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm−1. In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study., Special Issue "Polymer Nanocomposites", DC systems, Energy conversion & Storage, EEMCS - General

High current capability, good integration in urban area and zero external magnetic field are advantages of HTS cables that make them interesting for implementation in the Netherlands. So far experience with HTS cable projects is good, but still limited. Yet there is a need for a proper testing practice. Due to limited operational experience, various aspects remain to be studied. This paper focuses on electrical testing of electrical insulation, the application of power laws and the length effect. These issues are yet to be resolved, but the paper discusses their background and uncertainties. This may give direction to the ongoing studies in order to assure quality of HTS., DC systems, Energy conversion & Storage, EEMCS - General

Item does not contain fulltext, OBJECTIVES: Minimally invasive thoracoscopic epicardial pulmonary vein isolation (MIPI) has an important role in the surgical treatment of atrial fibrillation (AF). However, the management of recurrent atrial arrhythmias after MIPI and long-term success rate of catheter ablation have not been well studied. METHODS: Electrophysiological study was performed in 23 patients, 378 +/- 282 days after MIPI surgery, because of recurrent symptomatic atrial arrhythmias. RESULTS: A total of 20 patients presented with paroxysmal and persistent AF, 2 patients had a combination of AF and atrial tachycardia (AT) and 1 patient had a combination of AF and atrial flutter. All patients showed pulmonary vein (PV) reconnection. ATs were micro-re-entry PV-related ATs and atrial flutter was cavotricuspid isthmus dependent. Eighteen of 23 patients (78.3%) were free of atrial arrhythmias after one catheter ablation procedure at a mean follow-up of 50 +/- 16 months. Three patients underwent a second ablation procedure for recurrent AF and macro-re-entry left atrial flutter. Eventually 20 of 23 patients (87%) remained free of atrial arrhythmias after a mean of 1.1 +/- 0.3 ablation procedures. CONCLUSIONS: Catheter ablation of recurrent atrial arrhythmias following MIPI for paroxysmal and persistent AF is a feasible and effective treatment with a good long-term success rate. Reconnection of PVs accounts for most recurrences.

Item does not contain fulltext, BACKGROUND: Percutaneous renal denervation (RDN) has recently been introduced as a treatment for therapyresistant hypertension. Also, it has been suggested that RDN may be beneficial for other conditions characterised by increased sympathetic nerve activity. There are still many uncertainties with regard to efficacy, safety, predictors for success and long-term effects. To answer these important questions, we initiated a Dutch RDN registry aiming to collect data from all RDN procedures performed in the Netherlands. METHODS: The Dutch RDN registry is an ongoing investigator-initiated, prospective, multicentre cohort study. Twenty-six Dutch hospitals agreed to participate in this registry. All patients who undergo RDN, regardless of the clinical indication or device that is used, will be included. Data are currently being collected on eligibility and screening, treatment and follow-up. RESULTS: Procedures have been performed since August 2010. At present, data from 306 patients have been entered into the database. The main indication for RDN was hypertension (n = 302, 99%). Patients had a mean office blood pressure of 177/100 (±29/16) mmHg with a median use of three (range 0-8) blood pressure lowering drugs. Mean 24-hour blood pressure before RDN was 157/93 (±18/13) mmHg. RDN was performed with different devices, with the Simplicity™ catheter currently used most frequently. CONCLUSION: Here we report on the rationale and design of the Dutch RDN registry. Enrolment in this investigator-initiated study is ongoing. We present baseline characteristics of the first 306 participants.

Item does not contain fulltext, AIMS: Focal atrial tachycardia successfully ablated from the non-coronary cusp (NCC) is rare. Our aim was to describe the characteristics of mapping and ablation therapy of NCC focal atrial tachycardias and to provide a comprehensive review of the literature. METHODS AND RESULTS: Seven patients (age 40 +/- 9 years) with symptomatic, drug-refractory atrial tachycardia were referred for electrophysiological study. Extensive right and left atrial mapping revealed atrial tachycardia near His in all patients but either failed to identify a successful ablation site or radiofrequency applications only resulted in temporary termination of the tachycardia. Mapping and ablation of the NCC were performed retrogradely via the right femoral artery. Mapping of the NCC demonstrated earliest atrial activation during atrial tachycardia 38 +/- 14 ms (ranging 17-56 ms) before the onset of the P-wave. Earliest atrial activation in the NCC was earlier than earliest activation in the right atrium and left atrium in all patients. The P-wave morphology was predominantly negative in the inferior leads and biphasic in leads V1 and V2. The tachycardia was successfully terminated by radiofrequency application in 10 +/- 6 s (2-16 s), without complications. All patients were free of symptoms during a follow-up of 19 +/- 9 months. Literature search revealed 18 reports (91 patients) describing NCC focal atrial tachycardia, with 99% long-term ablation success with a 1% complication rate. CONCLUSION: Symptomatic focal atrial tachycardia near His may originate from the NCC and can be treated safely and effectively with radiofrequency ablation.

In this study, epoxy-cubic boron nitride composites are fabricated, and their dielectric response is investigated. They exhibit the same trend as epoxy composites reinforced with other filler types. Thus, at low filler concentrations, they exhibit a lower relative permittivity than neat epoxy. As the fill grade further increases, the relative permittivity of the composites increases as well. It is suggested that two competing mechanisms, namely polymer re-organization and water uptake, mainly determine the dielectric response of epoxy composites. The former is related to the decrease while the latter to the increase of the relative permittivity. The experimental results clearly verify that water uptake strongly depends on the filler concentration and not only affects the dielectric response of epoxy composites but also it is one of the main mechanisms which dictate their dielectric behavior., Electrical Sustainable Energy, Electrical Engineering, Mathematics and Computer Science

Poly(2-nonyl-2-oxazoline)80-stat-poly(2-dec-9?-enyl-2-oxazoline)20 and poly(2-dec-9?-enyl-2-oxazoline)100 can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced thiol-ene reaction. The complex permittivity of the corresponding networks increases with the temperature and decreases with the network density. In a frequency range from 10?2 to 106 Hz and at temperatures ranging from ?20 to 40 °C, the changes of the real part of the complex permittivity as well as the loss factor can be explained by interfacial polarization within the material. At a temperature of 20 °C and a frequency of 50 Hz, the permittivity of the crosslinked (co)poly(2-oxazoline)s covers a range from 4.29 to 4.97, and the loss factors are in the range from 0.030 to 0.093. The electrical conductivities of these polymer networks span a range from 5 × 10?12 to 8 × 10?9 S/m, classifying these materials as medium insulators. Notably, the values for the permittivity, loss factor and conductivity of these copoly(2-oxazoline)s are in the same range as for polyamides, and, hence, these copoly(2-oxazoline)-based networks may be referred to as “green” alternatives for polyamides as insulators in electronic applications., Electrical Engineering, Mathematics and Computer Science