Local Voltage Measurements Research Articles

A neural network-based scheme for fault diagnosis of power transformers

This research presents an artificial neural network (ANN)-based scheme for fault diagnosis of power transformers. The scheme is designed to detect the fault, estimate the faulted side, classify the fault type and identify the faulted phase. The proposed fault diagnosis scheme (FDS) consists of three hierarchical levels. In the first level, a pre-processing of input data is performed. In the second level, there is an ANN which is designed to detect the fault and determine the faulted side if any. In the third level, there are two sides diagnosis systems. Each system is dedicated to one side and consists of one ANN in series with four paralleled ANNs (for fault type classification). The proposed FDS is trained and tested using local measurements of three-phase primary voltage and primary and secondary currents. These samples are generated using EMTP simulation of the High Dam 15.75/500 kV transformer substation in Upper Egypt. All the possible fault types were simulated. The fault locations and fault incipience time were varied within each fault type. Testing results proved that the performance of the proposed ANN-based FDS is satisfactory.

Direct observation of lateral current spreading in ridge waveguide lasers using scanning voltage microscopy

We report results of two-dimensional (2D) local voltage measurement of the transverse cross section of operating multiquantum-well ridge-waveguide (RWG) lasers. We observe lateral nonuniformity of local voltage in the n-cladding layers of the laser and attribute the voltage variation to 2D carrier transport effect within the RWG lasers. The quantitative evaluation of this effect indicates the local vertical current density to be ∼40% smaller at the edge of the ridge than at its center. Our results demonstrate the strength and application of scanning voltage microscopy technique in quantitatively delineating 2D current flow in operating optoelectronic devices.

Electrical contrast observations and voltage measurements by Kelvin probe force gradient microscopy

Kelvin probe force gradient microscopy is proposed to image and measure local dc voltage variations using the double pass method. The various voltages between sensor and sample induce electrical force gradients that change the resonance of the sensor. Images of the various phase shifts show contrasts, which, as we demonstrate, can be interpreted in terms of local changes in voltage and capacitive coupling. The interest of this method for observation and local voltage measurements is demonstrated and explained.

Observations of self-organized InAs nanoislands on GaAs (0 0 1) surface by electrostatic force microscopy

Ambient non-contact electrostatic force microscopy (EFM) experiments in the force and force gradient modes were carried out on InAs nanoislands, MBE-grown on a GaAs surface and passivated with nitrogen. Typical EFM and Kelvin voltage images for the InAs nanoislands were obtained. Electrical force images in air can resolved single InAs nanoislands with a height down to 1 nm and a diameter of 15 nm. The contrast of the EFM images was strongly influenced by the tip-individual nanoisland capacitive coupling. Local Kelvin voltage measurements revealed variations in surface contact potential, V cp, between InAs nanoislands and the GaAs surface in the 40 mV range for the highest nanoisland. The V cp variations are attributed to the different nature of InAs and GaAs materials.

Dynamic performance assessment of an isolated wind-diesel power system with superconducting magnetic energy storage unit under turbulent wind and load disturbances

This paper presents modelling and control aspects of an isolated wind–diesel system equipped with a superconducting magnetic energy storage (SMES) unit. The SMES unit is located at the induction generators' terminal bus, for exchanging real and reactive powers in four quadrants, with the wind–diesel system. The system components are modelled by non-linear equations for accurate dynamic performance assessment and the SMES unit is modelled as a controllable current source. The control of the SMES unit is exercised through a multi-input–multi-output (MIMO) self-tuning regulator (STR). The STR uses the local voltage and frequency measurements and generates appropriate signals for the control of the SMES unit. The SMES coil current deviation forms a part of one of the regulated variables of the STR for achieving a continuous control. The complete model of the hybrid system is developed and the parameters of the STR are adjusted for quality improvement of the power supply under turbulent wind. The scheme is then tested for load disturbances. The simulation results show the positive impact of the proposed scheme on the quality of the power supply both under turbulent wind as well as load disturbances. Copyright © 2002 John Wiley & Sons, Ltd.

Local capacitance measurements on InAs dot-covered GaAs surfaces by scanning capacitance microscopy

Capacitance images responsible for surface depletion were observed on an InAs dot-covered GaAs surface by scanning capacitance microscopy. We performed local capacitance versus bias voltage measurements on quantum dots (QDs) and a wetting layer (WL) as well as conductance versus bias voltage (G–V) measurements. Both results indicate that the surface depletion is more suppressed beneath the QDs than under the WL. In addition, the conventional thermionic equation theory fitted to the measured G–V curves shows that the interface barrier height between the GaAs and the InAs QD increases as the QD size is reduced. We ascribe this result to the influence of the surrounding WL, whose surface Fermi level is strongly pinned at the midgap of the n-GaAs.

Robust decentralised control design using genetic algorithms in power system damping control

The paper presents the design of linear robust decentralised fixed-structure power system damping controllers using genetic algorithms (GA). The designed controllers follow a classical structure consisting of a gain, a wash-out stage and two lead-lag stages. To each controller is associated a set of three parameters representing the controller gain and the controller phase characteristics. The GA searches for an optimum solution over the parameter space. Controller robustness is taken into account as the design procedure considers a prespecified set of operating conditions to be either stabilised or improved in the sense of damping ratio enhancement. A truly decentralised control design is achieved as the loop control channels are closed simultaneously. The approach is used to design SVC and TCSC damping controllers to enhance the damping of the interarea modes in a three-area six-machine system. Local voltage and current measurements are used to synthesise remote feedback signals.

Robust decentralised design for multiple FACTS damping controllers

A systematic robust decentralised design procedure based on the H∞-optimisation technique for tuning multiple FACTS devices is presented. The design procedure uses a model-matching robustness formulation and requires the design of a parameter to achieve decentralised control. The approach is used to design damping controllers for an SVC and a TCSC to enhance the damping of the interarea modes in a 3-area 6-machine system. The feedback signals for the controllers are synthesised from the local voltage and current measurements.

A 1060 nm diode laser system for dynamically probing silicon detectors

Abstract We have constructed a 1060 nm laser system which has been used to dynamically probe silicon microstrip detectors. A diode laser is coupled to a single mode fiber with a less than 10 μm measured spot size. The laser is driven by a nanosecond pulse with sub-nanosecond rise and fall times. The fast response and small spot size allow for measurements of such quantities as time walk in microstrip detectors. The system has been used to generate 5–100 fC of charge in a 300 μm thick silicon microstrip detector. The laser also has been used in localized depletion voltage measurements and to test the integrity of sensors wire bonded to readout electronics.

Temperature field estimation using electrical impedance profiling methods. II. Experimental system description and phantom results.

An electrical impedance tomography system has been developed and tested for the purpose of thermal imaging. Since impedance changes with temperature, images of impedance subtracted from normothermic baselines will provide a map of temperature data. A system was designed to be operational at 10-50 kHz and to utilize 16 external electrodes around the periphery of a tissue-equivalent phantom encompassing the region of interest. These electrodes serve as current sources for the 5 mA constant-current inputs and are also used for reading differential voltages. Hyperthermia treatments for cancer require that internal thermometry probes be inserted into the tumour volume. Linear arrays of electrodes with thermometry tracks for micro-dimension thermometry serve this function, as well as providing localized voltage measurements in the region of interest. The embedded temperature sensors provide a quality assurance and calibration standard for the linear arrays in reconstruction of impedance profiles. Results of transient heating experiments with conductive and ultrasound heating are shown where image reconstruction is performed using a finite element model. Temperature predictions in these studies were accurate to better than 1 degree C on average when using information from surface electrodes combined with internal linear arrays. Maximum temperature errors, however, was found to be > 5 degrees C which suggests that further noise reduction during data acquisition and improvements in the reconstructions algorithms are needed.

Nanometer metal-oxide-semiconductor field-effect transistors: A flexible tool for studying inversion layer physics

The fabrication of multiterminal silicon MOSFET’s containing channel segments as narrow as 30 nm is described. These can be used for a variety of fundamental studies of quantum transport. In particular, in 100-nm channels, spatially localized voltage measurements can be made probing the scattering effects of a single electron trap.

Anode Phenomena in High-Current Accelerators

Quasi-steady MPD accelerators current conduction and power loss mechanism investigation through local anode fall voltage and current density measurements at different arc current levels