A Novel Electrical Sensor for Combined Online Measurement of Partial Discharge (OLPD) and Power Quality (PQ)

A novel inductive sensor has been developed that can be used for both for online partial discharge (OLPD) monitoring and power quality (PQ) monitoring. The sensor has been designed for attachment onto power cables with 50/60 Hz currents up to 800 A. The sensor comprises a high frequency (HF) winding to detect partial discharge (PD) pulses between 200 kHz and 30 MHz with a flat frequency response within this range. A low frequency (LF) winding is aimed at monitoring the power frequency (50/60 Hz) and its harmonics up to the 63rd order; it can also be used for current signature analysis (CSA) in rotating machines. A passive low-pass filter is integrated inside the sensor casing to suppress the higher frequencies not relevant to power quality monitoring. The sensor has a split-core design, making it easy to install and allows for retrofit installations. The combined sensor is well suited to places where space is limited such as compact cable boxes where it would be difficult to install two separate sensors. The sensor is primarily used for high voltage (HV) rotating machines (direct or VSD fed) and can be used in a variety of other applications such as monitoring of onshore and offshore wind farms. The paper begins by reviewing the main types of sensors used for partial discharge monitoring followed by the development of the novel sensor. Finally, two case studies where the sensor has been successfully installed are presented

Partial discharge testing of defects in dielectric insulation under DC and voltage ripple conditions

This paper details testing conducted on selected void defects in dielectric insulation samples under various HVDC voltage conditions. The aim of this work is to illustrate the type of PD activity that could be observed in HVDC insulation systems. Initially the samples were subject to HVAC excitation to confirm the defect type and establish the PD inception voltage. HVDC testing was then conducted using a ‘ramp and hold’ test technique with different hold voltages in the ramp determined from the measured HVAC inception voltage. The effect of harmonic ripple superimposed on the HVDC voltage waveform, which is typically a result of the converter switching operation, was also investigated. The findings from this study should provide network operators and insulation manufacturers a greater insight into the behavior of PD phenomena in solid insulation under HVDC conditions, enabling greater confidence in the diagnosis of defect type and severity in such systems

Practical aspects of partial discharge measurement for HVDC cables

High-voltage direct current (HVDC) cables are increasingly being installed to connect new offshore wind farms. Unplanned outages of these connectors can cause high economic impacts. Hence, there are requirements for condition-based maintenance that can improve operational reliability. Partial discharge (PD) is indicative of insulation defects. PD monitoring for AC cables is well established, but before applying the technique to HVDC cable connections, it is important to characterise PD behaviour under DC conditions and the attenuation in HVDC cables. This paper investigates PD activity under non-ideal DC stress, PD signal attenuation in HVDC cables, and electromagnetic noise in converter stations. Under the voltage of superimposed DC and harmonics, PD pulses tend to synchronise with the phase of harmonics. Therefore, synchronised recording of PD pulses can produce phase resolved patterns as an additional tool for insulation diagnostics. Modelling of attenuation in a HVDC transmission cable indicates that a detection bandwidth of tens of kHz to a few MHz may improve detection sensitivity when measuring PD current pulses over very long cable runs is carried out through sensors such as high frequency current transformers (HFCTs) installed at cable ends. Additionally, the RF spectrum measured in a converter station cable hall did not include any switching-related signals, demonstrating the viability of RF sensors based PD monitoring for the HV components associated with the cable connections

Successful Versus Failed Adaptation to High-Fat Diet–Induced Insulin Resistance: The Role of IAPP-Induced β-Cell Endoplasmic Reticulum Stress

ObjectiveObesity is a known risk factor for type 2 diabetes. However, most obese individuals do not develop diabetes because they adapt to insulin resistance by increasing beta-cell mass and insulin secretion. Islet pathology in type 2 diabetes is characterized by beta-cell loss, islet amyloid derived from islet amyloid polypeptide (IAPP), and increased beta-cell apoptosis characterized by endoplasmic reticulum (ER) stress. We hypothesized that IAPP-induced ER stress distinguishes successful versus unsuccessful islet adaptation to insulin resistance.Research design and methodsTo address this, we fed wild-type (WT) and human IAPP transgenic (HIP) rats either 10 weeks of regular chow or a high-fat diet and prospectively examined the relations among beta-cell mass and turnover, beta-cell ER stress, insulin secretion, and insulin sensitivity.ResultsA high-fat diet led to comparable insulin resistance in WT and HIP rats. WT rats compensated with increased insulin secretion and beta-cell mass. In HIP rats, in contrast, neither beta-cell function nor mass compensated for the increased insulin demand, leading to diabetes. The failure to increase beta-cell mass in HIP rats was the result of ER stress-induced beta-cell apoptosis that increased in proportion to diet-induced insulin resistance.ConclusionsIAPP-induced ER stress distinguishes the successful versus unsuccessful islet adaptation to a high-fat diet in rats. These studies are consistent with the hypothesis that IAPP oligomers contribute to increased beta-cell apoptosis and beta-cell failure in humans with type 2 diabetes

Metabolic regulation by p53

We are increasingly aware that cellular metabolism plays a vital role in diseases such as cancer, and that p53 is an important regulator of metabolic pathways. By transcriptional activation and other means, p53 is able to contribute to the regulation of glycolysis, oxidative phosphorylation, glutaminolysis, insulin sensitivity, nucleotide biosynthesis, mitochondrial integrity, fatty acid oxidation, antioxidant response, autophagy and mTOR signalling. The ability to positively and negatively regulate many of these pathways, combined with feedback signalling from these pathways to p53, demonstrates the reciprocal and flexible nature of the regulation, facilitating a diverse range of responses to metabolic stress. Intriguingly, metabolic stress triggers primarily an adaptive (rather than pro-apoptotic) p53 response, and p53 is emerging as an important regulator of metabolic homeostasis. A better understanding of how p53 coordinates metabolic adaptation will facilitate the identification of novel therapeutic targets and will also illuminate the wider role of p53 in human biology