Edris Agheb

Core loss behavior in high frequency high power transformers—II: Arbitrary excitation

High frequency high power transformers used in power electronic converters are frequently subjected to non-sinusoidal excitations. The main purpose of this paper is to study the effects of some general arbitrary waveforms on magnetic core loss in these transformers. First, using well-known empirical equations, general expressions were derived based on the parameters of the waveforms. Second, the impacts of different orders of voltage harmonics were investigated. Finally, capabilities of nanocrystalline and amorphous magnetic materials were compared. It is shown that the loss inside the core is highly sensitive to the rise time and duty cycle of trapezoidal and rectangular waveforms, respectively. Furthermore, although amorphous materials have higher saturation flux density, the total core loss inside the transformer designed using nanocrystalline material is considerably lower than the similar transformer with amorphous materials.

Core loss behavior in high frequency high power transformers—I: Effect of core topology

This two-part paper presents an overview of core loss computations performed in both time and frequency domains in order to evaluate their behavior in single phase transformers with different core topologies. Moreover, the effects of non-sinusoidal waveforms on well-known core loss calculation methods are investigated with both analytically and finite element calculations. Three well-known configurations of transformers utilized in high frequency high power applications are investigated, namely, the core type, the shell type, and the matrix transformer. Based on the results obtained from a large number of FEM simulations for different operating conditions, the efficiencies of the transformers are compared in terms of distribution of magnetic flux density, loss density, total core loss, and weight. The analysis shows that for lower range of frequency and power, the shell type core could be the favorable option, and on the other hand, core type seems to be an appropriate solution for higher values of the operating frequency and nominal power.

Medium frequency high power transformers, state of art and challenges

The worldwide increasing interests towards medium frequency high power transformers (MFHPTs) as a key element of high power converters in offshore wind farms and traction systems makes it a promising area of research. Since the electrical environment and excitations are different in these applications, conventional transformers are not applicable and hence new design procedures should be utilized. Several prototypes and design procedures have been proposed in recent years to optimize the efficiency and maximize the power density of such transformers. Consequently, in this paper, a review on the status of art, trends and challenges of such transformers is presented in detail. In addition, several potential future works are proposed and addressed completely.

Two dimensional simulation of Post Arc phenomenon in Vacuum Interrupter with Axial Magnetic Field contacts

The Post Arc (PA) phase of Vacuum Interrupters (VIs) and the effects of dominant physical parameters of vacuum arc investigated in this paper. 2-D movement of PA plasma in the presence of Transient Recovery Voltage (TRV) is simulated in a proper Finite Element Method (FEM).

Characterization of Magnetic Losses in the Transformer Tank Steel

The transformer tank is normally built of construction steel and has relatively large thickness of 1.2 mm for distribution up to 12 mm for large power transformers. In such thick materials, skin effect becomes much more significant than thin materials due to both frequency and non-linearity. The flux density in the tank can vary in a wide range of some mT to 1800 mT (in the case of having high zero sequence flux) leading to a large variation in the permeability and, consequently, in skin depth. Since the losses are high, the temperature rise can also be a main problem influencing the conductivity that must be considered in the loss calculations. The main contribution of this paper is to study the magnetic losses in the transformer tank steel through the measurements and finite difference-based numerical calculations. Using the loss separation principle, different loss mechanisms are investigated, and the behavior of each at the different level of inductions and frequencies is studied.

The peculiarities of Transient Recovery Voltage in presence of Post Arc Current in Vacuum Circuit Breakers

The post arc phase is a critical part in the current interruption process of Vacuum Circuit Breakers (VCB). During this step, the dielectric strength of VCB has to be recovered. In order to improve the performance of VCB, investigation of Post Arc Current (PAC) in the presence of Transient Recovery Voltage (TRV) is presented in this paper.