Real-time Current Measurement Research Articles

Distribution network supply restoration using measurement-based robust optimization approach

Most of the approaches developed to solve the supply restoration problem are based on the power flow models. Therefore, the practical implementation of these approaches requires a complete and accurate set of distribution network models, which are not available in many distribution networks. This paper proposes a new measurement-based approach for supply restoration which uses: (1) real-time current measurements gathered by the distribution system control center, and (2) topology of the distribution network, without requiring any other model information. The proposed approach formulates the supply restoration as the robust optimization problem in order to consider uncertainty involved with the used current measurements. The approach is applicable in distribution networks with distributed generators. The robustness and efficiency of the proposed methodology is demonstrated by calculating both a small test network and a 123-node network.

Event-Based Non-Intrusive Home Current Measurement Using Sensor Array

This paper presents a novel method for non-intrusive home current measurement using an array of magnetic field sensors. It is specifically designed for measuring the real-time currents on three wires, including two hot wires and one neutral wire, enclosed in the electric conduits of North American homes. The key idea is to extract information from appliance state changing events captured by sensor measurement changes. Since each detected event only corresponds to two wires between which the state-changing appliance is connected, the events can be clustered according to the wire connections. Wire position identification is formulated as a nonlinear least square problem and is efficiently solved. Then, real-time current measurement is achieved by using the trans-impedance matrix built based on the solved wire positions and the sensor parameters obtained from the manufacturing process. The proposed method is evaluated by extensive laboratory and field tests.

The influence of aqueous sodium dodecyl sulphate solution in the photoresponsivity of nitrogen doped graphene oxide photodetector

The homogeneity and agglomeration in graphene based photodetector plays an important role in the photoconduction. The influence of sodium dodecyl sulphate (SDS) solution in nitrogen doped graphene oxide (N-GO) is studied based on the photoresponsivity behaviour. One step hydrothermal method and drop casting technique are utilized to obtain N-GO photodetectors. High photoresponsivity about 1000 folds is achieved in N-GO prepared with SDS solution (N-GO/SDS) compared to the N-GO prepared without SDS solution. Raman spectrum also revealed a high intense D and G band as well as a slightly broaden 2D band due to sp2 hybridization. The fabricated device has exhibited wide range of responsivity to infrared (IR) laser 974 nm pulse and illumination. Real time current measurement in N-GO and current–voltage (I-V) characteristics in N-GO/SDS showed a significant photoconduction due to laser 974 nm illumination. The external quantum efficiency (EQE) in the N-GO/SDS solution is about 394830% compared to N-GO prepared without SDS, which is only 272%. The evaluated fall time at frequency modulation of 0.1 and 1 Hz for direct current (dc) bias voltage of 5.0 V found to be shorter compared to that of 2.5 V, whereas the fall time at high frequency modulation at 5000 Hz exhibited similar time around 77 μs.

The Liverpool Bay Coastal Observatory

The pilot coastal observatory in the eastern Irish Sea integrates (near) real-time measurements with coupled models in a pre-operational coastal prediction system. The aim is to develop the underpinning science for marine management, focusing on the impacts of storms, eutrophication and the relative importance of events viz-a-viz the mean. Real time current measurements are obtained from a seabed mounted acoustic Doppler current profiler; deployment started in August 2002, via acoustic modems and the Orbcomm satellite e-mail system, and from a shore based HF radar via telephone landlines. There are also real time measurements from a surface buoy and a directional wave buoy and from an instrumented ferry, all via Orbcomm. The measurements are integrated with a suite of nested 3-dimensional hydrodynamic and ecological models run daily, focusing on the Observatory area by covering the ocean/shelf of northwest Europe (at 12 km resolution), the Irish Sea (at 1.8 km) and Liverpool Bay (at 200-300m resolution). All measurements and model outputs are displayed on the Web-site (http://coastobs.pol.ac.uk).

Voltage and Current Sensor for State Estimation in Distribution Network with Generation

The penetration of Distributed Generation (DG) into the distribution networks has been increasing during the last decades. However, the increase of generation brings additional technical challenges for the Distribution Network Operators (DNOs). Thus, the integration of DG along with the improvement of the quality of service is driving the DNOs to actively control their networks. In order to achieve an effective control of the distribution network it is necessary to know the voltage across the network. Due to the lack of the real-time voltage measurers available onto the distribution network it would be necessary to estimate the voltage. Thus, as mentioned, the implementation of a state estimation method in distribution network is challenging due to the lack of real-time measurements available. The measurements considered in the distribution state estimation methods are predominantly off-time estimations of loads and therefore named pseudo measurements. However, estimate loads at the Low Voltage Switching Board are extremely difficult. To improve the quality of the distribution state estimation results, more real-time measurements are needed. However, the more measurements placed in the distribution networks the greater is the investment from the DNOs. Consequently, a trade-off between voltage accuracy, reliability and cost is required. Measurement placement method can be a solution to find the optimal compromise on the number of real-time measurement and consequent voltage accuracy. New types of measuring equipment such as voltage and current sensors can also help to reduce the initial investment costs. These sensors are considered in this work and are used for both protection and measurement functions. Also, these sensors can be directly connected to the communication equipment and thus resulting in a reduction of the number of system components and wiring. This paper presents both a method to place voltage and current sensors across the MV network and a distribution state estimation algorithm. The single-phase distribution state estimation algorithm determines the voltage magnitudes across the MV network and their associated accuracy. The state estimation algorithm integrates realtime current measurements from the current sensors at the network, the DG site and the MV busbar at the primary substation site. The distribution state estimation algorithm is based on the weighted least squares approach. To minimize the estimated voltage inaccuracy, the placement method determines the best location for a minimum number of voltage and current sensors. The results showed that current and voltage measurement together can improve the estimated voltage magnitude accuracy. The method to place voltage and current sensors along with the distribution state estimation algorithm may allow distribution network operators to actively control their network and thus increase the amount of generation onto their distribution networks with an improvement in power quality.

A study of the energy consumption characteristics of cryptographic algorithms and security protocols

Security is becoming an everyday concern for a wide range of electronic systems that manipulate, communicate, and store sensitive data. An important and emerging category of such electronic systems are battery-powered mobile appliances, such as personal digital assistants (PDAs) and cell phones, which are severely constrained in the resources they possess, namely, processor, battery, and memory. This work focuses on one important constraint of such devices-battery life-and examines how it is impacted by the use of various security mechanisms. In this paper, we first present a comprehensive analysis of the energy requirements of a wide range of cryptographic algorithms that form the building blocks of security mechanisms such as security protocols. We then study the energy consumption requirements of the most popular transport-layer security protocol: Secure Sockets Layer (SSL). We investigate the impact of various parameters at the protocol level (such as cipher suites, authentication mechanisms, and transaction sizes, etc.) and the cryptographic algorithm level (cipher modes, strength) on the overall energy consumption for secure data transactions. To our knowledge, this is the first comprehensive analysis of the energy requirements of SSL. For our studies, we have developed a measurement-based experimental testbed that consists of an iPAQ PDA connected to a wireless local area network (LAN) and running Linux, a PC-based data acquisition system for real-time current measurement, the OpenSSL implementation of the SSL protocol, and parameterizable SSL client and server test programs. Based on our results, we also discuss various opportunities for realizing energy-efficient implementations of security protocols. We believe such investigations to be an important first step toward addressing the challenges of energy-efficient security for battery-constrained systems.

A Robust Framework for Cable Rating and Temperature Monitoring

This paper introduces a robust framework for the temperature monitoring of power cables based on real-time current measurement only, or current measurement in conjunction with cable surface or sheath temperature measurement. The method is based on modeling the temperature response of a cable by summing an appropriate number of exponential functions. These functions are related to a thermal ladder circuit for installations that can be analyzed in such terms, or are mathematically fitted to numerically simulated results for those that cannot. The robustness of the method stems from the fact that exponential functions can be easily rendered into an inherently stable real-time formulation depending on the temperatures calculated at the previous increment and final conditions. The hypothetical final conditions are established at each time interval by simple steady-state calculations based on the present temperatures. This allows entry into territory that is forbidden for normal superposition methods, namely, a thermally unstable environment. Despite erroneous initial conditions, the algorithm will converge and it has the added merit of being extremely light, computationally speaking. The method provides an alternative method for transient cable rating, is inherently suited for real-time implementation, and provides a framework that can accommodate a changing thermal environment caused by, for example, such a phenomenon as moisture migration.

Ocean surface current measurements by an L band two‐frequency microwave scatterometer

Real time current measurements with an L band pulsed two‐frequency microwave scatterometer (2FS) were carried out from the German North Sea Research Platform (Forschungsplattform Nordsee) during the 1979 Marine Remote Sensing (Marsen) experiment. The principle of this remote sensing technique consists of measuring the phase velocity of a long ocean wave by resonant scattering of a beat wave produced by two microwave signals. The difference between the measured phase velocity and the phase velocity, as calculated from the dispersion relation for still water, represents a weighted average of the ocean current near the surface. Current measurements over full tidal cycles in various wind conditions (up to 18 m s−1) are presented. At high wind speeds, pronounced differences are found between the 2FS measurements and the in situ current measurements made at depths of 9 m and 23 m. These differences can be explained as the effect of the wind stress acting on the upper layer of the ocean. The measurements indicate that the interaction of the tide‐ and wind‐driven currents strongly depends on the parallel and antiparallel orientation of the currents. The accuracy of the measurements reported here is approximately ±0.12 m s−1, but this can, in principle, be improved.