China
Africa
Explore chapters and articles related to this topic
Low Frequency Cables and Shielding
Published in Michael P. Perry, Low Frequency Electromagnetic Design, 2019
To combat the problem of increasing ac resistance in cables, a number of techniques have been developed. One of the most revered of these is to employ insulated transposed conductors in a form sometimes called “Litz” wire. (The name Litz is derived from the German word “Litzendraht.”) Litz wire generally comprises a number of strands of wires which are separately insulated using rubber, plastic, or varnish on the outer surface. Uniform distribution of current among individual strands is accomplished by “transposing” each wire at regular intervals along the cable. Transpositioning can occur in a continuous, discrete, or random pattern. The principle of transposed conductors is that each individual wire exchanges relative position with every other wire in the cable. A complete transposition is accomplished when each strand occupies every relative position in the cable over a specific length. When a sufficient number of complete transpositions occur over a given length of cable, the inductance and resistance of all the wires are theoretically equal, and therefore the total cable current divides equally among all strands. When the current is uniformly distributed across the cable, and the wire diameter is much smaller than a “skin-depth,” a “dc current distribution” is obtained, presumably resulting in greatly reduced ac resistance for a given cable diameter.
Choice of System Voltage (AC/DC) for a Standalone Nanogrid
Published in Kailas L. Wasewar, Sumita Neti Rao, Sustainable Engineering, Energy, and the Environment, 2022
Sachin P. Jolhe, G.A. Dhomane, M. D. Karalkar
High-frequency ac is one of the options for the DG. But it is not usually employed as a transmission frequency of power systems. However, for distributing power in buildings, high frequency ac system has been organized with the frequency of 20 kHz [25]. The main advantage of the system is that it has a small size of magnetic components and inductive power transfer. The drawback of dielectric losses and skin effect is reduced by the use of Litz wire. The use of Litz wire renders this option impractical (economic viability) for longer distance transmission, while this transmission frequency may be a useful for small distances. Simulation model for 20 KHz frequency transmission is as shown in Figure 10.4.
Fields, Forces, and Materials for LEMs
Published in Ion Boldea, Linear Electric Machines, Drives, and MAGLEVs Handbook, 2017
The frequency or (and) slot height hslot increases lead to ζ increase and thus give rise to notable skin effect (increased resistance and reduced leakage (slot) inductance in ac). Now the bar coil is used typically for high currents and, even if the frequency is not high, the skin effect is important: So the bar is made of quite a few conductor layers transposed such that each of them occupies all positions in the slot, along machine length (Roebel bar). At high frequency, the conductor is broken into thin wires, which are again transposed (Litz-wire) to reduce the skin effect to values typical to the single elementary conductor standing alone.
Optimal Design with Generalized Inductance Calculation for IPTs Using a Spiral Rectangular Coil Pair
Published in Electric Power Components and Systems, 2022
Litz wires are generally used due to the skin and proximity effect in the wireless power transfer systems. AWG38 is recommended for operation in the 50-100 kHz range [36]. If no additional cooling method is used, the current density should be below 5 A / mm2, in the system with continuous energy transfer [37,38]. E-bikes are generally used outdoors and the ambient temperatures may be high. Therefore, for a better and reliable design, the maximum current density 3 A / mm2 has been selected in this study. Copper losses of litz-wire can be modeled by using parameters such as resistivity of copper, length and radius of litz wire, as well as total number of litz wire, radius of strand, angular frequency and permeability of air [39]. However, very good estimation of coil resistance is not a criterion for determining optimal IPT in this study. It is effective only in the efficiency calculation. In this study, instead of detailed copper loss model of litz wire, the resistance of litz wire is considered as a copper coil resistance (25). Here ρ is the resistivity of the copper. Depending on the number of turns, approximate conductor resistance of ith coil can be calculated by total winding length () . is calculated from the coil dimensions (26). Where and are average edge lengths of the inner winding, is the diameter of the conductor, and is the gap between the two windings.
Design and Analysis of quasi Resonant high gain Impedance source DC-DC converter for DC microgrid
Published in International Journal of Electronics, 2023
Harinaik Sugali, Shelas Sathyan, N. J. Merlin Mary
The transformer core is selected based on the area product method (). Litz wires are used to minimize skin effect and associated losses due to high frequency operation.