Martin Paar

Possible Solutions to Problems of Voltage Asymmetry and Localization of Failures in MV Compensated Networks

The compensated networks are affected by the phase capacity asymmetry of wiring, which causes the unbalancing of the phase voltages in the tuned condition of the arc-suppression coil. In the especially unfavourable cases this effect reduces the possibility of network operation with the tuned arc-suppression coil. The operation with the arc-suppression coil out of tune is accompanied by higher values of the fault currents during the ground faults and the natural frequency of the course of recovery voltage in the network after switching off or interrupting the ground fault. These disadvantages can only be removed by efficient elimination of the phase asymmetry. The new methods of eliminating the phase capacity asymmetry allow for controlling the phase asymmetry size (its reduction as well as its possible increase), they keep it within a specified tolerance band (Uo value in the tuned condition of the arc-suppression coil is typically maintained at levels from 1% to 4% of the network voltage phase value). The new methods of elimination of the phase capacity asymmetry have favourable effects on the network operation during the ground fault and do not reduce the protecting elements sensitivity to high-ohm ground faults. By improving the accuracy of the arc-suppression coil tuning the safety of the compensated networks operation can be enhanced. The other properties of the whole system of phase capacity asymmetry elimination designed to increase the compensated networks operation safety, to improve the reliability of ground- fault protections and to locate the fault areas, can be fully utilized

Utilization of Particle Swarm Optimization Algorithm for Optimization of MV Network Compensation

This article describes the possibilities of solving optimal distribution of capacitors by particle swarm optimization (PSO) used in parallel compensation of medium voltage (MV) distribution network. PSO is a suitable tool for solving combinatorial problems benefiting from low requirements for criterial function. An algorithm looks for such a parameter set-up that has a minimum price and a minimum level of the total power losses and a minimum cost of capacitors and minimum maintenance expenses, all of this under given limitations. Its functionality is demonstrated on the example of a power network.

Some features of possible solutions of installing telecontrolled section switches and reclosers in the MV overhead network

The paper discusses some features of possible solutions of placing telecontrolled section switches and reclosers in the MV overhead network. The presented results are derived from examples of real MV feeders. The reliability and economical indices being evaluated have been obtained from the nonsequential Monte Carlo simulation. The financial evaluation of reliability is based on the customers standard of electricity supply continuity which is being introduced by some regulatory offices. This standard defines the limit of the annual number of supply interruptions and the limit of the total annual duration of supply interruptions sustained by the customer. Costs of penalty payments then follow from exceeding some of these limits. The inclusion of both limits into the standard and thus into the economical evaluation results in changing the relation between the net present value of possible solutions and the reliability index SAIDI. It also leads to preferring reclosers to telecontrolled section switches in optimal variants of equipping the MV feeders with telecontrolled elements.

The phase sequence selection for cables lines at Extra High Voltage level

The article deals with the hygienic limits in the Czech Republic for electric and magnetic fields radiated by Extra High Voltage cables with focus on phase sequence selection for minimization of magnetic fields in the surroundings of cables. Developments in EHV cables domain are discussed as well.

Optimization of the compensation of a meshed MV network by a modified Genetic Algorithm

This article discusses the utilization of a modified genetic algorithm (GA) for the optimization of the shunt compensation in meshed and radial MV distribution networks. The algorithm looks for minimum costs of the network power losses and minimum capital and operating costs of applied capacitors, all of this under limitations specified by a multicriteria penalization function. The parallel evolution branches in the GA are used for the purpose of the optimization acceleration. The application of this GA has been implemented in Matlab. The evaluation part of the GA implementation is based on the steady-state analysis using a linear one-line diagram model of a power network. The results of steady-state solution are compared with the results from the DIgSILENT Power Factory program. Its practical applicability is demonstrated on examples of 22 kV radial and meshed overhead distribution networks.