Volume 20, Issue 2 -

In this paper, the possibility of using lithium-ion batteries in hybrid stand-alone power sources is considered. The article gives a comparative analysis of the energy and performance characteristics, the service life of lead-acid and lithium-ion batteries. It is shown that the longer service life and the specific energy density, the absence of the need for constant monitoring of the main parameters and the ability to preserve the original capacity at increased discharge currents, open the possibility of using lithium-ion batteries in hybrid stand-alone power sources.

Existing over-temperature supervising (OTS) systems available for switch cabinet, even those based on advanced optical fiber sensing technology, are unable to satisfy the critical requirements such as reliability, safety, practicability and economy simultaneously. In this paper, a novel OTS scheme that take a special kind of gas to carry the signal indicating the over-temperature state of a switch cabinet is developed elaborately. Serving for the CO 2 gas which has comprehensive and overwhelming superiorities in situation of OTS, a gas storage unit that is composed of a hard plastic crust and an inner tubular airbag, a gas releasing mechanism that consists of bimetallic and acupuncture, and a gas sensing terminal are designed artfully. The overall OTS system is finally developed by integrating these three parts with a background server via wireless communication technology. The advantages of the proposed system, such as high reliability and safety, fast response speed and universal applicability have been proven by lab tests and field experiments. Moreover, the inherent low cost and easy installation and maintenance features of our scheme facilitate the development of OTS systems for other electrical devices in power system.

Due to the increasing penetration of wind power into the distribution network, preserving system security and reliability becomes a significant challenge for the system operator. In the smart grid environment, the demand side is required to take more responsibilities to accommodate the uncertainty of wind power generations, known as demand response (DR). To enable this feature in the utility grid, system-wide costs, which include metering, communication and load control system upgrade cost and incentive cost for customers, should be considered in assessing cost-effectiveness. This paper proposes a novel optimization model for demand response facility (DRF) investment to determine the DR sizing and siting. Robust optimization is adopted to maintain overall economic benefit and distribution network operation security. The problem is formulated as a bi-level mixed-integer program. A column-and-constraint generation algorithm (C&CG) combined with outer-approximation (OA) linearization method is employed to solve this problem. Numerical tests on a modified IEEE 33-bus distribution network illustrate the effectiveness and validation of the proposed model.

The conical spacers made of epoxy resin are widely used in Gas Insulated System(GIS) for electrical insulation as well as mechanical support to the conductor. Electric stress on the surface of the spacer as well as at the triple junction is of major concern while designing the spacer for the Ultra High Voltage Alternating Current (UHVAC) GIS. To reduce the possibility of the flashover, the tangential field at the concave and convex surfaces is to be within limits. This paper presents a stepwise method for the reduction of the electric field at the spacer surface and at the triple junction by geometry shape optimization. The electric field has been calculated by solving Laplacian equation by Finite Element Method(FEM). Optimization has been realized by incorporating Nelder-Mead(NM) algorithm with FEM solution. The tangential field at the concave and convex surface of the conical spacer has been optimized by changing the shielding ball shape and metal inert in the spacer as well as by changing the curvature and thickness of spacer near to the high voltage conductor. The results demonstrate the reduction in the principle stress for the optimized geometry shape and the stress at the triple junction. The improvement in the electric field uniformity for the spacer surface is seen in the final optimized geometry

With the latest smart technologies in the electricity sector, the consumers of electricity got the opportunity to reduce their electricity consumption cost by participating in the demand response programs offered by the utility companies. In this paper, a model of energy management system is introduced for the energy scheduling at home. Residential automatic smart appliances of general use are selected for energy scheduling. The energy controlling device in the EMS model receives the real time electricity price signals from the utility company and schedule the appliances according to the user requirements in such a way so that the electricity consumption cost could be minimized. The appliances are scheduled under real time pricing combined with inclined block rate pricing scheme so that the peak to average ratio of power could be maintained in the satisfactory range. This helps the utility companies in maintaining the system reliability. For the solution of the scheduling problem, particle swarm optimization algorithm is used due to its effectiveness and easy implementation. Finally, the results have been compared and verified against the results achieved by genetic algorithm.

In distributed generation (DG) systems, the rate of change of voltage and the rate of change of frequency are the two most common and widely used simple and low-cost passive islanding detection schemes. Unfortunately, these passive islanding detection schemes find limitation for detecting the islandings that cause very small power imbalance. In this paper, an improved passive islanding detection scheme is proposed by using the two newly derived indices from the sequence components of the current signal with the conventional voltage and frequency parameters. The performance of the proposed scheme is tested for numerous islanding and non-islanding cases generated on IEEE Std 399–1997 and IEC microgrid model distribution system integrated with both inverter-interfaced and synchronous DGs through PSCAD/EMTDC. The obtained results confirm the effectiveness of the proposed scheme.

This paper presents an approach using Pigeon Inspired Optimization (PIO) for selective harmonic elimination in a cascaded H-bridge (CHB) multilevel inverter fed with unequal dc sources. The aim of this work is to find the optimal combination of switching angles, such that the lower order harmonics are eliminated and the output voltage is constant irrespective of voltage change in the input side. This paper the PIO has been used to find the optimal angles for a 7-level inverter and the method can be scaled to any number of levels. To show the effectiveness of PIO the results have been compared with other evolutionary algorithms such as genetic algorithm (GA), particle swarm optimization (PSO). An adaptive switching angle strategy has also been developed using ANN to make the proposed strategy suitable to the real-time applications. In order to verify the results, an experimental prototype of 7 level CHB has been developed in the laboratory using dSPACE ds1104 R&D controller board. The results show that the PIO is the most accurate and fastest evolutionary algorithm for switching angle optimization and the experimental results are in close agreement with the simulation results.

Partial discharge location in gas insulated switchgears is important for timely identifying incipient problem and taking remedial actions to prevent later catastrophic breakdowns. This paper presents a new system including sensing terminals and hand-held intelligent terminals to locate partial discharge. Sensing terminals, housing the sensors, are attached to outside enclosure walls of the switchgear to collect acoustic signals, which are transmitted wirelessly to the hand-held terminals. The acoustic vibration caused by the discharge will propagate from the source, resulting in the highest intensity at the sensor closest to the discharge. By examining the signal signatures of the distributed sensors, the location of the partial discharge can be derived. The system is applied in both staged simulation environment and actual factory high voltage tests. The results have demonstrated that the system developed is highly effective in locating partial discharge in gas insulated switchgears and is suitable for practical applications.

This paper presents the development of three comprehensive static models of a 3-phase induction machine in phase frame of reference for interfacing with multi-phase power flow programs. The models developed are based on specified slip or specified power, either at the rotor shaft or at the terminals of the induction machine. The development of these models also takes into consideration load torque characteristics. The mathematical formulation of these models is based on branch constraint approach instead of the traditional node constraint approach. This facilitates the arbitrary connections of the induction machine, namely wye, wye-grounded, wye-grounded through impedance, and delta. The models are ideally suited for application in the present trend of operating power and distribution networks with high penetration of renewable energy sources (RES). These models assist in evaluating the performance of wind generators operating under unbalanced system conditions and also in selection of proper phase wise compensation. These static models compute the correct initial operating conditions of induction machines for 3-phase transient stability studies and EMTP-type simulation studies, to evaluate the precise dynamic behaviour of the power system. The procedure for integrating these models in the multi-phase power flow program is also described. The performance of the developed multi-phase power flow program, including static induction machine models, has been evaluated for various power network sizes. The results obtained are verified against the existing literature to clearly demonstrate the efficacy of the proposed methodology.

This paper presents an indirect method for measuring the mechanical power produced by three-phase induction motors. The proposed technique is based on the hypothesis that three-phase induction motors are balanced systems that transform electrical power into mechanical one. The measurement of a single phase current is used to estimate the mechanical power generated at the axis. The relationship between electric current and mechanical power is generally non-linear. By expressing the quantities in p.u., this trend is approximated with a second order polynomial. From the analysis of the mechanical power characteristics related to 13 motors we obtained the parameters of the interpolating parabolic curves of motors from 1.1 kW to 75 kW rated power. The proposed technique can be easily adopted in order to monitor the mechanical power of three phase induction motors using only one phase current transducer. Starting from the motor nameplate no experimental measurement or other data are necessary to estimate the mechanical power. This technique can be widely used in low cost multipoint measurement system able to monitor the mechanical power where no other transducer or voltage divider are necessary.

The feasibility of integration of Battery Energy Storage System (BESS) with a three-phase AC grid is being investigated in this paper. A converter is an inevitable part of a modern DC generating system. The link between the grid and the BESS is established through a Voltage Source Converter (VSC). Therefore, the converter can be utilized to dispatch the DC generated power to the connected AC grid and at the same time provides reactive power compensation and load harmonic compensation throughout the day. The DC bus voltage control of the converter system is carried out to keep the power factor always at unity, irrespective of the charging state of the battery source. The charging and discharging of the connected battery energy storage system are carried out through a bidirectional DC-DC converter. Adaptive hysteresis band current control (AHCC) scheme is employed to produce the switching signals. Finally, its performance is compared with the traditional hysteresis band control technique.