Band 11, Heft 3

This paper presents a novel driveline where the load and the energy source are operated at different voltage levels and they are galvanically insulated. The element that couples both part of the driveline is a Two Voltage Level Machine (TVLM). The machine is formed of a self-excited rotor and a stator with two sets of electrically isolated windings for adjustable speed drive applications. Both sets of these three phase windings are independently operated at different voltages. The equivalent circuit of the TVLM is deduced and phasor diagrams are presented. A complete driveline is simulated and the performance of the complete system is discussed. The driveline is applicable in flywheel energy storage systems for vehicles and power conditioning in renewable energy production.

State estimation plays an important role in real time security monitoring and control of power systems. There are many problems in the implementation of state estimator for large scale networks due to measurement errors, weights given and the numerical ill-conditioning associated with the solution techniques. In this paper a new formulation using linear programming approach is presented. The formulation is devoid of weights and errors associated with the measurements are taken care of in constraints. The non linear problem is linearized at previous operating state and constraints are set up using flow mismatches. The implementation of the formulation exploits sparse features of the network matrices and avoids matrix inversions. Upper bound optimization technique is employed to solve the linear programming problem. Illustration of the proposed approach on sample 3-bus and 6-bus systems and a practical Indian Southern grid 72 bus equivalent system are presented.

With deregulation, the total transfer capability (TTC) calculation, which is the basis for evaluating available transfer capability (ATC), has become very significant. Total transfer capability (TTC) is an important index in power markets with large volume of interarea power exchanges and wheeling transactions taking place on hourly basis. Its computation helps to achieve a viable technical and commercial transmission operation. The aim of the paper is to evaluate TTC in the interconnections and also to improve it using reactive optimization technique and unified power flow controller (UPFC) device. TTC computation is carried out considering normal and contingency conditions such as single line, tie line and generator outages. Base and optimized results are presented, and the results show how reactive optimization and UPFC help to improve the system conditions and tie flows. Repeated power flow method is used for transfer capability computation due to its ease of implementation. A case study is carried out on a 72-bus equivalent system, which is a real-life system, a part of Indian Southern grid. The developed procedure is successfully applied to the three-area 72-bus system. Parameters like voltage magnitude, L-index, minimum singular value and MW losses are computed to analyze the system performance.

This paper proposes a fast restoration strategy of distribution systems using an enhanced differential evolution (EDE) approach. Service restoration of distribution systems is an emergent task that must be performed rapidly by the system operators. Basically, it is a complicated combinatorial optimization problem, often having many candidate solutions to be evaluated by the operators. To improve the efficiency of restoration and reduce the burden on the operators, this paper proposes an EDE method combining variable scaling differential evolution (VSDE) algorithm and ant system (AS) to solve the combinatorial optimization problem. To verify the effectiveness of the proposed method, a typical distribution system of the Taiwan Power Company (TPC) was tested and compared with the existing methods. The results show the proposed method was superior to the existing methods in terms of convergence time and the obtained restoration plan.

A new probabilistic model to simulate generation investment and risks applicable in a deregulated market is proposed. In this process, probabilistic production cost simulation is applied to simulate energy dispatches. Electricity prices are simulated from a modified Black-Scholes-Merton (BSM) based price simulation model. In this work, the existing BSM model is enhanced thus making it possible to simulate the demand and supply conditions in price determination. A complete investment analysis model is then developed by integrating the above two simulation processes. Using this model, generator investors can analyze the impacts on the anticipated revenue due to different plant efficiency, availabilities, bilateral contract markets and changes in demand and supply conditions. Simulated results show that the proposed model is able to analyse the viability in generation investment with much simplicity.

During power system restoration, it is necessary to check the phase angle between two buses before closing circuit breakers to connect a line between them. A novel approach for reducing large standing phase angle (SPA) based on Genetic Algorithm (GA) is presented in this paper. The proposed approach starts with a state estimation on Wide Area Monitoring System (WAMS) data measurements and considering power system operation and angular stability constraints, seeks an optimal control action scenario for reducing SPA. Since these constraints are evaluated based on WAMS data, the presented approach is considerably high speed and accurate. As an optimization problem, objective function of the proposed approach is to minimize variation from the current state of the power system. Simulation results on the IEEE 118 bus test system clearly show efficiency of the approach.

With the increased use of partial discharge tests to assess the conduction of shielded distribution cable, PD signal frequency properties of such cables have become increasingly important. It is desirable to detect and locate the PD in the cable before breakdown occurs. Understanding the propagation phenomena of the PD signal in XLPE cable is important to detect and locate the PD signal. In this paper, transmission properties of PD signal were measured and analyzed on a 30m length and 15m length of 11 kV XLPE cable in the laboratory . The experimental results show a good agreement with the theoretical analysis. The paper describes the test results and discusses the PD signal attenuation in time and frequency domain and discusses this with reference to practical PD detection.