Volume 10, Issue 1

A power transformer, when energized at no-load, may have transient currents up to 100 times that of the steady state magnetizing current. This inrush current has several detrimental effects on power quality and may damage sensitive equipment connected to the system. In this paper, a power electronic based control circuit is developed, which estimates the last remnant and, utilizing this data, it controls the next re-energization instant to achieve inrush free switching. An equivalent circuit model of a transformer is also presented to simulate the transient dynamic performance of a transformer for any arbitrary switching operation.

Distribution power flow methods by and large consider the substation voltage to be known and fixed. This type of model is not suitable for stressed system conditions. Although some power flow software may allow an equivalent representation of the transmission and sub-transmission system, the procedure for the determination of such an equivalent is not available in literature. Hence, this paper presents a very simple three-phase power system equivalent model, which can be obtained with negligible computational effort from real time measurements, for an unbalanced operating system. The validity of the proposed model is demonstrated through studies for two sample systems.

Results from experiments on a direct driven permanent magnet synchronous generator are presented. Dynamic simulations have been performed using the finite element method in order to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface-mounted, arched, permanent magnets. A complete experimental setup has been used consisting of a motor, a frequency converter, a gearbox and electrical loads. The generator is connected to a purely resistive load. Measurements have been performed for different rotational speeds and different loads. Furthermore, the generator has been studied for the realistic wind turbine loading conditions for operation at the optimum tip speed ratio. The variable speed operation in a wind turbine is evaluated and discussed. The agreement between experimental results and simulations based on finite element calculations is high, indicating precise simulations. The measurement errors are calculated and discussed. Furthermore, other sources of error are suggested and discussed that could explain the differences between the simulations and the measured data.

In developing countries, a high rate of growth in the demand for electric energy is felt, and so the addition of new generating units becomes inevitable. In deregulated power systems, private generating stations are encouraged to add new generations. Some of the factors considered while placing a new generating unit are: availability of resources, ease of transmitting power, distance from the load centre, etc. Finding the most appropriate locations for generation expansion can be done by running repeated power flows and carrying system studies like analyzing the voltage profile, voltage stability, loss analysis, etc. In this paper a new methodology is proposed which will mainly consider the existing network topology. A concept of T-index is introduced in this paper, which considers the electrical distances between generator and load nodes. This index is used for ranking the most significant new generation expansion locations and also indicates the amount of permissible generations that can be installed at these new locations. This concept facilitates for the medium and long term planning of power generation expansions within the available transmission corridors. Studies carried out on an EHV equivalent 10-bus system and IEEE 30 bus systems are presented for illustration purposes.

This paper is the outcome of an attempt in mining recorded power system operational data in order to get new insight to practical power system behavior. Data mining, in general, is essentially finding new relations between data sets by analyzing well known or recorded data. In this effort we make use of the recorded data of the Southern regional grid of India. Some interesting relations at the total system level between frequency, total MW/MVAr generation, and average system voltage have been obtained. The aim of this work is to highlight the potential of data mining for power system applications and also some of the concerns that need to be addressed to make such efforts more useful.

In this paper, an improved load sharing control scheme is presented, which is able to improve the transient response and power sharing accuracy of parallel-connected inverters used in microgrid. It also shows how the improved droop method can be easily adapted to account for the operation of parallel-connected inverters, providing good performance under the variation and disturbance of loads, as well as achieving good steady-state objectives and transient performance. Two DSP-based single-phase Microgrid inverters are designed and implemented. Simulation and experimental results are all reported, confirming the validity of the proposed control technique.

Wind power has emerged as a promising renewable energy resource. A wind power plant, normally located in an area with reliably favorable wind speed, is connected to the grid through a transmission line. This paper presents a steady-state characteristic study of a DFIG-based wind energy conversion system (WECS) that is integrated into the power grid through a transmission system. Steady-state models in a d-q reference frame are developed for a single wind turbine, a simplified wind power plant, and an integrated WECS and grid system. In addition, a transient simulation system is built to validate the accurateness of the steady-state results by using MatLab SimPowerSystems. An integrative study is performed to investigate WECS parametric data simultaneously as the number of DFIG wind turbines connected to a wind farm changes under constant turbine driving torque and driving power conditions. Parallel and series compensations, usually used to improve WECS performance, are investigated. A comparative study is presented to illustrate the characteristic difference between WECSs using fixed-speed induction generators and variable-speed DFIGs.