Search

As the second part of the investigation on vibration characteristics of ± 800 kV converter transformers, this part focuses on load conditions. A full-load thermal stability test is carried out on 12 YY and YD converter transformers in a converter station. Vibration, voltage, current, and other important information are collected by online monitoring devices. Vibration amplitude, vibration spectrum, dominant frequency, vibration power ratio of frequency band, vibration power entropy, and odd–even harmonic ratio under different load conditions are calculated and studied to evaluate the vibration state. Theoretical analyses of winding electromagnetic force and vibration acceleration are carried out and results show that the harmonic currents make the dominant frequency shift to 300 Hz or 400 Hz. Most vibration characteristics are sensitive to load rate changes. The odd–even harmonic ratio is sensitive to filter disconnection and reconnection. The results of this study reveal the vibration regularity and corresponding mechanism and can contribute to further study on vibration assessment of ± 800 kV converter transformers under load conditions.

The purpose of this work is to compare, with the same digging diagrams, the velocity, accelerations and dynamic performances of two excavators with different arm configurations. In particular, constructive solutions involving the use of two and three mobile arms will be examined. For excavators the different construction geometry (2-3 arms) is mainly dictated by reasons of use, in fact the 3 arms solution is normally used in areas that allow poor mobility of vehicle and present obstacles during the excavation phase. The dynamic comparison between the two solutions is performed on real working conditions to which they can be subjected during the exercise. The elaborations are performed both analytically and numerically. Essentially the analysis shows that in the condition of leveling and lifting at minimum distance from the rotation axis the dynamic performances are similar, there are significant differences in the lifting condition at the maximum distance. The diversity also implies significant variations in the forces of the hydraulic cylinders used to move both the load and the arms, an aspect which finds greater emphasis even in the case in which the arms are made by adopting unconventional materials for their realization as aluminum and composites.

In a cross-country skiing competition, the time difference between the winner and the skier coming in at second place is typically very small. Since the skier spends much of the energy on overcoming resistive forces, a relatively small reduction in these forces can have a significant impact on the results. The resistive forces come partly from the friction, at the tribological interface between the ski and the snow, and as with many tribological processes, the characterisation of its origin plays an important role in determining the frictional properties. Furthermore, in cross-country ski friction, there are several scales impacting the frictional performance, with the major contributors being the ski-camber profile and ski-base structure. Macro-scale measurements of the ski-camber profile under loading are often used to determine how adequate the ski is for use under specific conditions. The characteristic properties usually assessed are the force required to collapse the ski in order to obtain a certain camber height, the topography of the kick-wax zone, and the length (determined by simple means) of the frictional interfaces associated with the rear- and front glide zones, i.e., the apparent contact length. These measurements are, however, commonly performed by loading the ski against a much stiffer counter surface than snow and this affects the quantification of the characteristic properties. To date, some mathematical models have been proposed, but there is no reliable approach for determining the macro-scale properties of the contact between a cross-country ski and a counter surface using simulations. In the present paper, an Artificial Neural Network (ANN) has been trained to predict the ski-camber profile for various loads applied at different positions. A well-established deterministic approach has been employed to simulate the contact between the ANN-predicted ski-camber profile and a linearly elastic body with a flat upper surface, representing the snow. Our findings indicate that this method is feasible for the determination of relevant macro-scale contact characteristics of different skis with snow. Moreover, we show that the apparent contact area does not linearly depend on the load and that the material properties of the counter surface also exert a large impact when quantifying the apparent contact area and the average apparent contact pressure.

A three-phase interleaved (LC)(L)-type dc–dc series-resonant converter with a capacitive output filter using fixed frequency control is proposed. The converter operations for different modes during different intervals have been presented using the operating waveforms. The converter is analysed using the approximate analysis approach, and the design procedure is illustrated with a design example. PSIM simulation results for the designed converter are given for load and input voltage variations. It is shown that the converter operates in zero-voltage switching (ZVS) at the minimum input voltage and for different load conditions. On the other hand, at the maximum input voltage from full load to light load, leading switches operate with ZVS, whereas lagging switches operate with zero-current switching (ZCS).

This paper develops a new field weakening method for an integrated permanent magnet synchronous machine vehicle drive. This method adopts both the DC-link and the rotor speed as a feedback signals to generate the demagnetising current reference. This eliminates the effect of the rotor speed on the FW controller dynamics and ensures stable operation across the whole range of speeds. Mathematical analysis of the system is used to design the controller gains to achieve the desired dynamic response. A maximum torque per ampere (MTPA) strategy is included in the control design, with a linearised function to reduce the computational demand. Experimental results show stable and satisfactory operation at different speeds and load conditions. They also illustrate smooth transition between the MTPA operation and the FW operation when the rotor speed crosses base speed.