Alicia J. Allen

Waveform characterization of animal contact, tree contact, and lightning induced faults

In this paper signal processing tools are used to uncover common and unique characteristics of faults resulting from animal contacts, tree contacts and lightning. For each fault type a large number of voltage and current waveform data sets measured at monitoring stations on distribution systems are analyzed. The characteristics include but are not limited to the presence of impulse-like oscillations, the number of phases involved, the duration of fault event, the phase angle, the time of day, the spectral content in the time-frequency and time-scale domains, the rate of rise of voltage or current, and the arc voltage. An individual characteristic alone is insufficient to provide an estimate of the fault type. However, by combining common and unique characteristics extracted from a fault event, it may be possible to estimate the fault type accurately.

Algorithm for screening PMU data for power system events

Wide Area Monitoring Systems (WAMS) are a Smart Grid technology which can enhance real-time situational awareness for power sytem operators. WAMS are created from a network of synchronized measurement devices taking voltage and current measurements from the power system. This network is also known as a synchrophasor network. A synchrophasor network was created at the University of Texas at Austin to obtain real power system measurements for power system analysis. The network is continuously operating and recording voltage phasor data (voltage magnitude, angle, and frequency) at a rate of 30 data points per second. Because of the high volume of PMU data generated it is difficult to detect and analyze power system events of interest. To help power system operators more easily monitor the power system and easily detect events in PMU data, two different types of methods were created to automatically screen the data for events. The first method screens a small window of PMU voltage data and detects events based on a variety of techniques. The second method is an off-line method that detects events based on the magnitude of low frequency oscillations in PMU voltage data.

Waveform characteristics of underground cable failures

In this paper unique characteristics of underground cable faults are extracted from the voltage and current waveforms recorded by power quality monitors. These characteristics are used to classify cable faults on the basis of fault duration, specific cable equipment failure and root-cause behind the fault. They are also used to distinguish underground cable faults from other overhead distribution line faults. Waveform signature analysis, wavelet transforms and arc voltage during the fault event is used for cable fault identification and classification.

Regenerated cellulose micro-nano fiber matrices for transdermal drug release

In this work, biobased fibrous membranes with micro- and nano-fibers are fabricated for use as drug delivery carries because of their biocompatibility, eco-friendly approach, and potential for scale-up. The cellulose micro-/nano-fiber (CMF) matrices were prepared by electrospinning of pulp in an ionic liquid, 1-butyl-3-methylimidazolium chloride. A model drug, ibuprofen (IBU), was loaded on the CMF matrices by a simple immersing method. The amount of IBU loading was about 6% based on the weight of cellulose membrane. The IBU-loaded CMF matrices were characterized by Fourier-transform infrared spectroscopy, thermal gravimetric analysis, and scanning electron microscopy. The test of ibuprofen release was carried out in an acetate buffer solution of pH5.5 and examined by UV-Vis spectroscopy. Release profiles from the CMF matrices indicated that the drug release rate could be determined by a Fickian diffusion mechanism.

Modeling Distribution Overcurrent Protective Devices for Time-Domain Simulations

Poor overcurrent protective device coordination can cause prolonged and unnecessary voltage variation problems. The coordination of many protective devices can be a difficult task and unfortunately, device performance and accuracy are not evaluated once the device settings are chosen and deployed. Ideally, an automated system would interrogate system data at the substation and estimate voltage variations and assess protective device performance. To test the accuracy of the automated system, a simulation model is developed to generate test data. The time-domain overcurrent protective device models can be used to estimate the duration of voltage sag during utility fault clearing operation as well. This paper presents the modeling of overcurrent protective device models created in a time-domain power system simulator. The radial distribution simulation, also made in the same time-domain software, allows testing of different overcurrent protection device settings and placement.

Voltage phase angle variation in relation to wind power

Monitoring of some of the effects of wind power on the transmission grid is possible from 120 V wall outlet measurements. The penetration levels of wind power are reflected in synchronized phasor measurements taken by the independent synchrophasor network located at the University of Texas at Austin. The independent synchrophasor network is unique because it takes single-phase synchronized voltage phasor measurements from 120 V wall outlets. These measurements are shown to be suitable for observing some of the effects of wind power penetration on power system parameters such as the voltage phase angle. This is the beginning of research on the topic of quantifying the effects of wind power on the grid as seen in Texas Independent Synchrophasor Network measurements.

Phasor measurement unit placement Algorithm

The importance of having phasor measurement units or PMUs in an electric grid is widely recognized. However, the number of PMUs on a large system is limited by cost and the placement of PMUs must be addressed. The main objective of this research is to create an algorithm to identify buses that are the best candidates for PMU placement based on certain requirements. The monitoring of certain grid events like transmission line failure or generator failure must be possible from the selected PMU locations. In addition, the PMUs must be distributed evenly so that critical parts of the grid are visible. At the same time, there should be no or little redundancy in the PMU readings unless it is intentional to provide additional data reliability. The algorithm, once developed, is then applied to the electric network directed and operated by the Electric Reliability Council of Texas (ERCOT). After analyzing the results, clusters or group of buses are identified in each operational area in the ERCOT gird, where the PMUs should be located. The PMU can be located at any of the bus in the cluster. In future it is desirable to expand the algorithm to consider the geographical divisions in the ERCOT grid along with the commercial divisions.

Validation of distribution level measurements for power system monitoring and low frequency oscillation analysis

The University of Texas at Austin introduced the Independent Synchrophasor Network in order to monitor events and analyze low frequency oscillations from the electric power grid through PMU measurements taken at customer level voltage (120 V). The purpose of this paper is to present validation of the quality of these distribution level measurements for power system monitoring and analysis. Three different steps are used in the validation process. In the first step, the distribution voltage phase angle measurements are plotted with and compared to the state estimated transmission level voltage phase angle. The second step is the comparison of distribution level PMU measurements to transmission level PMU measurements during a power system transient response. The frequency, voltage magnitude, and voltage phase angle are analyzed during a unit trip event. In the final step, the modal frequency and damping estimates are used to illustrate the accuracy of distribution measurements as representative of the power systems ambient response. Because of the location of the PMUs within the network, it will also be possible to measure the effects of wind power on the rest of the grid.

Unique waveform characteristics of current limiting fuse operations

This paper identifies and quantifies the unique characteristics of current-limiting fuse operation as seen in the current and voltage waveforms recorded at a monitoring station located upstream from the fault. Characteristics that can be used to identify current-limiting fuse operations by visual inspection are described. More characteristics are extracted using signal processing methods. These characteristics include but not limited to the duration of the event, point on the waveform where the event starts and ends, the rate of rise of the voltage and current at the start of the event, and the thermal energy in the fuse during the event. These methods are applied to data collected by a number of utilities and the results tabulated. In the future, the results can be used to automatically classify events that are recorded by power quality monitors.

Commonly used thiol-containing antioxidants reduce cardiac differentiation and alter gene expression ratios of sarcomeric isoforms

ABSTRACT Reactive oxygen species (ROS) scavengers such as beta‐mercaptoethanol (BME) and monothiol glycerol (MTG) are extensively used in stem cell research to prevent cellular oxidative stress. However, how these antioxidant supplements impact stem cell cardiac differentiation, a process regulated by redox‐signaling remains unknown. In this study, we found that removal of BME from the conventional high‐glucose, serum‐based differentiation medium improved cardiac differentiation efficiency by 2–3 fold. BME and MTG treatments during differentiation significantly reduced mRNA expression of cardiac progenitor markers (NKX2.5 and ISL1) as well as sarcomeric markers (MLC2A, MLC2V, TNNI3, MYH6 and MYH7), suggesting reduced cardiomyogenesis by BME or MTG. Moreover, BME and MTG altered the expression ratios between the sarcomeric isoforms. In particular, TNNI3 to TNNI1 ratio and MLC2V to MLC2A ratio were significantly lower in BME or MTG treated cells than untreated cells, implying altered cardiomyocyte phenotype and maturity. Lastly, BME and MTG treatments resulted in less frequent beating, slower contraction and relaxation velocities than untreated cells. Interestingly, none of the above‐mentioned effects was observed with Trolox, a non‐thiol based antioxidant, despite its strong antioxidant activity. This work demonstrates that commonly used antioxidant supplements may cause considerable changes to cellular redox state and the outcome of differentiation. HIGHLIGHTS&bgr;‐mercaptoethanol (BME) and monothiolglycerol (MTG) reduce cardiac differentiation.BME and MTG treatments decrease TNNI3/TNNI1 and MLC2V/MLC2A expression ratios.BME and MTG treatments reduce beating rates and contraction/relaxation velocities.Trolox, a strong ROS scavenger, does not inhibit cardiac differentiation.