Three-phase

About: Three-phase is a research topic. Over the lifetime, 16801 publications have been published within this topic receiving 159477 citations.

Multiple-frequency three-phase load flow for harmonic analysis

Abstract: A multiple-frequency three-phase load-flow model was developed in this paper. There are two new submodels including the fundamental power flow (FPF) and harmonic frequency power-flow (HPF) model. In FPF, models of electrical elements and PV buses were treated in the form of current injections in a transmission system. The standard Fourier analysis was used to deal with the harmonic loads to get injection currents. With harmonic currents as equivalent current sources, the HPF can be derived. Besides, the decoupled fast version of FPF and HPF, called DFPF and DHPF, were also proposed in this paper. Test results show that the proposed general-purpose methods are better performers than conventional power-flow solutions and are very robust.

Inhomogeneity effects in HTS coated conductors used as resistive FCLs in medium voltage grids

Abstract: For resistive fault current limiters (RFCLs) based on high temperature superconducting coated conductors (HTS-CCs), inhomogeneity, in terms of critical current and geometrical imperfections such as stabilizer and substrate thicknesses, plays a very important role and it may limit the penetration of such devices into the electrical market. This paper presents an electrothermal model, developed in SimPowerSystem™, able to describe the transient response of HTS-CC candidates with different degrees of inhomogeneity, both in terms of critical current and of stabilizer thickness. Critical current inhomogeneity has been modeled with Gaussian distributions. The layer thicknesses used in the simulations have been chosen by fitting the temperature dependence of real tape resistances. Our approach considers relative inhomogeneity positions as well as thermal conduction along the HTS-CC length. The model is tuned using experimental measurements made on ReBaCuO coated conductors. A new dynamical thermal calibration of the model is proposed using finite element method calculations. Inhomegeneity effects with different possible faults (e.g. three phase and single phase short-circuit) are presented.

Soft-Switching AC-Link Three-Phase AC–AC Buck–Boost Converter

Abstract: In this paper, the soft-switching ac-link ac-ac buck-boost converter will be studied in more detail. This single-stage converter, which is, in essence, an extension of the dc-dc buck-boost converter, can be an excellent alternative to dc-link converters. Being a buck-boost converter, this converter is capable of both stepping-up and stepping-down the voltage. The link current and voltage are both alternating, and their frequency can be as high as permitted by the switches and the sampling time of the microcontroller. This eliminates the need for dc inductors or dc electrolytic capacitors, and the main energy storage element is an ac inductor (L). Moreover, in this converter, galvanic isolation can be provided by adding a single-phase high-frequency transformer to the link. Therefore, the proposed converter is expected to be more compact compared to the conventional dc-link converter. The other advantage of this converter is the soft switching of the switches, which is feasible by adding a small capacitor (C) to the link. In this paper, the design and analysis of this converter will be studied in detail. In order to accurately analyze this converter, the effect of the LC link resonance on the performance of the converter will be studied. This analysis helps in evaluating the performance of the converter at low power levels when the resonating time of the LC link is not negligible. Using this analysis, the link peak current and the link frequency may be calculated at any point of operation. The accuracy of this method is verified through simulations and experiments. Detailed comparison of the proposed converter with the dc-link converter will be also presented in this paper. It will be shown that, despite having more switches, the current rating of the switches is lower in this converter. Moreover, the efficiencies of the two converters will be compared. Finally, the performance of the soft-switching ac-link ac-ac buck-boost converter is experimentally evaluated in this paper. It will be shown that the converter has the possibility of changing both the frequency and the voltage. Both step-up and step-down operations will be verified through experiments.

Protective system for electrical appliances

Abstract: An a-c power supply for a load such as a household appliance, including a line wire, a neutral wire and a ground wire, has a safety switch and an overload-sensing resistor inserted in its line wire and also comprises a ground-fault detector in the form of a differential transformer with a toroidal core traversed by the line and neutral wires. The safety switch, which may be a manually resettable circuit breaker or an armature of a self-locking relay, has an operating winding in series with an SCR connected between a positive and a negative terminal, one terminal being connected via respective diodes to the line and neutral wires, the other terminal being connected via respective diodes to the neutral and ground wires. The gate circuit of the SCR includes the secondary of the differential transformer, the secondary of another transformer connected across the overload-sensing resistor, a pair of voltage dividers -- one inserted between the positive terminal and the neutral wire, the other inserted between the same terminal and the ground wire -- for detecting ground loss, neutral loss, line/neutral reversals and excessive neutral-to-ground voltages, and Zener diodes for detecting overvoltages and undervoltages. In a three-phase system, the two terminals are both connected via respective diodes to all three phase wires in parallel. With the use of a pair of triggerable semiconductors (SCRs or triacs) in lieu of a single SCR, the operating winding can be tied directly to the line wire while being connected to the other two wires through the two semiconductors, respectively.