Search

For optimal coordination of directional overcurrent relay we propose to consider operation characteristics, pickup current and time multiplier setting of relays as optimization parameters. Each parameter is optimized independently with the aid of linear formulation of the coordination problem. First, optimal discrete values of pickup current are selected. Second, adequate operation time characteristics of relays are selected. Third, optimal discrete values of time multiplier setting are determined. The proposed method is tested on two networks: an 8-bus system and the IEEE 30-bus system. Its performances are evaluated and compared with those of the linear and nonlinear programming techniques.

International audience; Rare earth permanentmagnet synchronousmachines with the pulsewidth modulated supply are exposed to magnets'heating due to harmonic fields, which rotate in relation to rotor. In caseswhen skin effect is negligible, the corresponding eddy-current losses in magnets can be reduced by segmentation of magnets. In this paper, we propose an analytical method to evaluate the effect of both circumferential and axial segmentations on losses' reduction in various conditions, concerning the skin effect. With the skin effect operating, the magnets' division may lead to increase rather than decrease of the eddy-current losses. A criterion to determine range of parameters leading to this unexpected situation is presented. Finite-element calculation confirms the results of the analysis.

This article analyzes the drawbacks of linear programming methods to solve the directional over-current relay coordination problem. The solution infeasibility of these methods is due to selectivity constraints, which reduce the upper bound of the time multiplier setting of some relays. This infeasibility can be avoided by making the upper bound of the time multiplier setting insensible to selectivity constraints. With the proposed algorithm based on this idea, the constraints causing infeasibility are identified in order to change their position in relation to possible solution areas. This change is achieved by increasing the relay pickup currents. The proposed algorithm is tested and evaluated on the IEEE 14-bus and 30-bus networks. The results show that the previously infeasible solution of linear programming becomes feasible with high efficiency.

The PWM-supplied permanent magnet synchronous machines are exposed to magnets' heating due to harmonic fields which rotate in relation to rotor. The corresponding losses can be calculated by FE simulation for each frequency, with superposition of all components of the losses. In certain conditions three dimensional modelling is required to get enough precision. However, time-stepping 3D finite element methods coupled with motion equations can lead to excessive computational time. Then a locked rotor approach with current sheet rotating may be interesting. In this case however, the superposition doesn't really work unless special procedure is applied. Magnetic loss dissipation cannot be correctly calculated with simple superposition of individual fields, e.g. the 5th and 7th harmonic rotating in opposite direction. This is because the resulting field has an alternative component with dissipative effects depending on its position. They will be more important if the component oscillates in the middle of magnets and less important in the middle of gap between them.